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Physical Activity
Guidelines Advisory
Committee Report,
2008
To the Secretary of
Health and Human Services
U.S. Department of Health and Human Services
The findings of this report are those of the Physical Activity
Guidelines Advisory Committee. They do not necessarily reflect the
views of the Office of Disease Prevention and Health Promotion or the
U.S. Department of Health and Human Services.
Suggested citation: Physical Activity Guidelines Advisory Committee. Physical
Activity Guidelines Advisory Committee Report, 2008. Washington, DC: U.S.
Department of Health and Human Services, 2008.
Physical Activity
Guidelines Advisory
Committee Report, 2008
Prepublication Copy
Issued June 2008
DEPARTMENT OF HEALTH AND HUMAN SERVICES Office of the Secretary
Assistant Secretary for Health
Office of Public Health and Science
Washington D.C. 20201
May 23, 2008
The Honorable Michael O. Leavitt
Secretary of Health and Human Services
200 Independence Avenue, S.W.
Washington, D.C. 20201
Dear Secretary Leavitt,
On behalf of the entire 2008 Physical Activity Guidelines Advisory Committee, we are
very pleased to submit the Physical Activity Guidelines Advisory Committee Report,
2008.
You charged our committee to “…review existing scientific literature to identify where
there is sufficient evidence to develop a comprehensive set of specific physical activity
recommendations.” The Committee's report documents scientific background and
rationale for the 2008 edition of the Physical Activity Guidelines for Americans. The
Committee also identified areas where further scientific research is needed.
The Committee’s review and deliberations clearly demonstrated that sedentary behavior
confers substantial health risks throughout the lifespan. The health benefits of being
habitually physically active appear to apply to all people regardless of age, sex,
race/ethnicity, socioeconomic status, and to many people with physical or cognitive
disabilities. The amount and intensity of physical activity needed to achieve many health
benefits is well within the capacity of most Americans .and can be performed safely. This
report provides the scientific basis for these conclusions and the development of federal
physical activity guidelines.
For the entire Committee, we want to thank you for the opportunity to support your
Prevention Priority. Over the past twelve months, the Committee members and
consultants worked exceptionally long and hard to conduct the extensive scientific review
that made this report possible. Despite this task being added to their usual busy schedules,
they met tight deadlines, provided insight and education to one another, and unselfishly
worked to develop a consensus report. Thus, we wish to thank you for assembling a
committee of outstanding professionals who are not only knowledgeable and highly
productive but also most pleasant in character.
U.S. Public Health Service
It is important to emphasize that this report could not have been completed without the
outstanding support of all the HHS staff who assisted us throughout the entire process.
We are very grateful for their substantial assistance in developing an extensive electronic
searchable literature database for use by the Committee and for their excellent logistical
and management support in all aspects of the Committee's work. Special recognition
goes to RADM Penelope Slade Royall and CAPT Richard Troiano of the Office of
Disease Prevention and Health Promotion for their tireless dedication in the coordination,
and ultimate completion, of this project. This report greatly benefits from the expert
editing provided by Anne Brown Rodgers, who helped us present information that is
useful and readable, and from the careful work of Reba Norman, who ensured the
completeness and accuracy of the report’s extensive reference lists.
Our review documents very strong scientific evidence that physically active people have
higher levels of health-related fitness, a lower risk of developing a number of disabling
medical conditions, and lower rates of various chronic diseases than people who are
inactive. Given Americans' low rates of participation in physical activity and high
prevalence of chronic diseases and associated disabilities, this report is particularly
timely. It provides the necessary foundation for HHS to proceed to develop Physical
Activity Guidelines for Americans, 2008 and related policy statements. Strong federal
guidelines, policies, and programs regarding physical activity should be an essential
component of any comprehensive disease prevention and health promotion strategy for
Americans. Committee members are committed to the broad dissemination of this report
and the ensuing guidelines. Please do not hesitate to contact us or any of the Committee
members if we can be of further service.
Sincerely,
[Signed May 23, 2008]
William L. Haskell, Ph.D
Chair, 2008 Physical Activity Guidelines Advisory Committee
Prevention Research Center, School of Medicine, Stanford University
[Signed May 23, 2008]
Miriam E. Nelson, Ph.D.
Vice-Chair, 2008 Physical Activity Guidelines Advisory Committee
John Hancock Center for Physical Activity and Nutrition
Friedman School of Nutrition Science and Policy, Tufts University
Contents
Physical Activity Guidelines Advisory Committee Members ....................Front Matter-1
Part A: Executive Summary..............................................................................................A-1
The Physical Activity Guidelines Advisory Committee..............................................A-1
Report Contents..............................................................................................................A-2
Review of the Science on Physical Activity and Health ..............................................A-2
Research Recommendations........................................................................................A-10
Part B: Introduction...........................................................................................................B-1
Setting the Stage for Physical Activity Guidelines for Americans.............................B-1
The Physical Activity Guidelines Advisory Committee..............................................B-2
A Systematic Review of the Evidence on Physical Activity and Health....................B-3
Contents and Organization of the Physical Activity Guidelines Advisory
Committee Report ..........................................................................................................B-5
Part C: Key Terms .............................................................................................................C-1
Physical Activity and Exercise ......................................................................................C-1
Physical Fitness...............................................................................................................C-4
Health ..............................................................................................................................C-6
Study Design and Measurement ...................................................................................C-6
Publication Types ...........................................................................................................C-7
Reference List .................................................................................................................C-8
Part D: Background ...........................................................................................................D-1
Introduction ....................................................................................................................D-1
Some Issues Regarding Dose Response ........................................................................D-1
Recent Trends in Physical Activity in the United States ............................................D-9
Development of Physical Activity Guidelines in the United States..........................D-17
Reference List ...............................................................................................................D-28
Part E: Integration and Summary of the Science ...........................................................E-1
Introduction ....................................................................................................................E-1
Summarizing the Evidence............................................................................................E-1
Integrating the Evidence: Questions and Answers About the Health
Benefits of Physical Activity ........................................................................................E-22
Reference List ...............................................................................................................E-35
Part F: Scientific Literature Search Methodology..........................................................F-1
Background.....................................................................................................................F-1
Conceptual Framework .................................................................................................F-1
Physical Activity Guidelines Advisory Committee Report v
Contents
Research Questions ........................................................................................................F-1
Operational Plan ............................................................................................................F-3
Literature Review...........................................................................................................F-4
Part G. Section 1: All-Cause Mortality ......................................................................... G1-1
Introduction ................................................................................................................. G1-1
Review of the Science .................................................................................................. G1-1
Overview of Questions Addressed .........................................................................................G1-1
Data Sources and Process Used to Answer Questions ...........................................................G1-1
Question 1: Is There an Association Between Physical Activity and All-Cause
Mortality? If So, What Is the Magnitude of This Association?..............................................G1-2
Question 2: What Is the Minimum Amount of Physical Activity Associated With
Significantly Lower Risk of All-Cause Mortality? ................................................................G1-5
Question 3: Is There a Dose-Response Relation Between Physical Activity and AllCause Mortality? ..................................................................................................................G1-14
Question 4: What Is the Shape of the Dose-Response Relation Between Physical
Activity and All-Cause Mortality? .......................................................................................G1-17
Question 5: Is the Relation Between Physical Activity and All-Cause Mortality
Independent of Adiposity? ...................................................................................................G1-20
Overall Summary and Conclusions ......................................................................... G1-21
Reference List ............................................................................................................ G1-23
Part G. Section 2: Cardiorespiratory Health................................................................ G2-1
Introduction ................................................................................................................. G2-1
Review of the Science .................................................................................................. G2-1
Overview of Questions Addressed .........................................................................................G2-1
Data Sources and Process Used To Answer Questions ..........................................................G2-2
Special Considerations and Limitations .................................................................................G2-3
Question 1: What Is the Relationship Between Physical Activity and
Cardiovascular Morbidity and Mortality? ..............................................................................G2-4
Question 2: What Are the Dose-Response Relations Between Physical Activity and
Cardiovascular Morbidity and Mortality? ............................................................................G2-12
Question 3: What Is the Relationship Between Physical Activity and
Cerebrovascular Disease and Stroke? ..................................................................................G2-15
Question 4: What Is the Relationship Between Physical Activity and Peripheral
Arterial Disease? ..................................................................................................................G2-17
Question 5: What Is the Relationship Between Physical Activity and Hypertension? ........G2-19
Question 6. What Is the Relationship Between Physical Activity and Atherogenic
Dyslipidemia?.......................................................................................................................G2-21
Question 7: What Is the Relationship Between Physical Activity and Vascular
Health?..................................................................................................................................G2-23
Question 8: What Is the Relationship Between Physical Activity and
Cardiorespiratory Fitness?....................................................................................................G2-28
Overall Summary and Conclusions ......................................................................... G2-39
Physical Activity Guidelines Advisory Committee Report vi
Contents
Research Needs.......................................................................................................... G2-40
Reference List ............................................................................................................ G2-41
Part G. Section 3: Metabolic Health.............................................................................. G3-1
Introduction ................................................................................................................. G3-1
Review of the Science .................................................................................................. G3-2
Overview of Questions Asked................................................................................................G3-2
Data Sources and Process Used To Answer Questions ..........................................................G3-2
Question 1. Does Physical Activity Have a Role in Preventing or Treating
Metabolic Syndrome?.............................................................................................................G3-3
Question 2. Does Physical Activity Have a Role in Preventing and Treating Type 2
Diabetes? ................................................................................................................................G3-9
Question 3. Does Physical Activity Have a Role in Reducing Macrovascular Risks
in Type 2 Diabetes? ..............................................................................................................G3-15
Question 4. Does Physical Activity Have Benefits for Type 1 Diabetes?............................G3-20
Question 5. Does Physical Activity Have a Role in Preventing and Treating
Diabetic Microvascular Complications? ..............................................................................G3-22
Question 6: Do Physical Activity and Exercise Have a Role In Preventing
Gestational Diabetes? ...........................................................................................................G3-28
Overall Summary and Conclusions ......................................................................... G3-29
Research Needs.......................................................................................................... G3-29
Reference List ............................................................................................................ G3-30
Part G. Section 4: Energy Balance ................................................................................ G4-1
Introduction ................................................................................................................. G4-1
Review of the Science .................................................................................................. G4-1
Overview of Questions Addressed .........................................................................................G4-1
Data Sources and Process Used to Answer Questions ...........................................................G4-1
Caveats ...................................................................................................................................G4-2
Question 1: How Much Physical Activity Is Needed for Weight Stability and
Weight Loss?..........................................................................................................................G4-2
Question 2. How Much Physical Activity Is Needed to Prevent Weight Regain in
Previously Overweight Individuals? ......................................................................................G4-8
Question 3. What Is the Effect of Physical Activity on Body Composition
Parameters (e.g., Waist Circumference, Intra-Abdominal Fat, Abdominal
Adiposity, Total Body Fat) That Are Specifically Related to Metabolic Disorders?...........G4-10
Question 4: What Effects Do Sex and Age Have on the Role of Physical Activity in
Energy Balance?...................................................................................................................G4-13
Question 5: How Do the Physical Activity Requirements for Weight Maintenance
Differ Across Racial/Ethnic and Socioeconomic Groups?...................................................G4-15
Overall Summary and Conclusions ......................................................................... G4-19
Physical Activity, Weight Stability, and Weight Loss .........................................................G4-19
Physical Activity and Weight Regain...................................................................................G4-20
Physical Activity and Body Composition Parameters..........................................................G4-20
Physical Activity Guidelines Advisory Committee Report vii
Contents
The Effect of Sex and Age on Physical Activity and Energy Balance.................................G4-21
Physical Activity Requirements Across Race/Ethnicity and Socioeconomic Groups .........G4-21
Research Needs.......................................................................................................... G4-21
Physical Activity, Weight Stability, and Weight Loss .........................................................G4-21
Physical Activity and Weight Regain...................................................................................G4-22
Physical Activity and Body Composition Parameters..........................................................G4-22
The Effect of Sex and Age on Physical Activity and Energy Balance.................................G4-22
Physical Activity Requirements Across Race/Ethnicity and Socioeconomic Groups .........G4-22
Reference List ............................................................................................................ G4-23
Part G. Section 5: Musculoskeletal Health ................................................................... G5-1
Introduction ................................................................................................................. G5-1
Review of the Science .................................................................................................. G5-2
Overview of Questions Addressed .........................................................................................G5-2
Data Sources and Process Used to Answer Questions ...........................................................G5-2
Question 1. Does Physical Activity Reduce the Incidence of Osteoporotic
Fractures? ...............................................................................................................................G5-3
Question 2. Does Physical Activity Reduce Risk of Osteoporosis by Increasing, or
Slowing the Decline in, Bone Mineral Density or Bone Mineral Content? .........................G5-11
Question 3. Does Physical Activity Reduce or Increase the Incidence of
Osteoarthritis? ......................................................................................................................G5-17
Question 4. Is Physical Activity Harmful or Beneficial for Adults With
Osteoarthritis or Other Rheumatic Conditions? ...................................................................G5-24
Question 5. Does Physical Activity Increase or Preserve Muscle Mass Throughout
the Lifespan? Does Physical Activity Improve Skeletal Muscle Quality, Defined as
Changes in Intrinsic and Extrinsic Measures of Force-Generating Capacity, Such as
Strength or Power? ...............................................................................................................G5-31
Overall Summary ...................................................................................................... G5-38
Reference List ............................................................................................................ G5-38
Part G. Section 6: Functional Health ............................................................................ G6-1
Introduction ................................................................................................................. G6-1
Conceptual Model and Terminology......................................................................................G6-1
Functional Health in Middle-Aged and Older Adults ............................................................G6-2
The Importance of Reducing Disability and Falls in Older Adults ........................................G6-3
Review of the Science .................................................................................................. G6-3
Overview of Questions Addressed .........................................................................................G6-3
Data Sources and Process Used To Answer Questions ..........................................................G6-4
Question 1: In Middle-Aged and Older Adults Who Do Not Have Severe
Functional or Role Limitations, Does Regular Physical Activity Prevent or Delay
the Onset of Substantial Functional Limitations and/or Role Limitations? ...........................G6-4
Physical Activity Guidelines Advisory Committee Report viii
Contents
Question 2: In Older Adults Who Have Mild, Moderate, or Severe Functional or
Role Limitations, Does Regular Physical Activity Improve or Maintain Functional
Ability and Role Ability With Aging? .................................................................................G6-10
Question 3: In Older Adults Who Are at Increased Risk, Does Regular Physical
Activity Reduce Rates of Falls and Fall-Related Injuries?...................................................G6-16
Overall Summary and Conclusions ......................................................................... G6-21
Research Needs.......................................................................................................... G6-22
Reference List ............................................................................................................ G6-23
Part G. Section 7: Cancer ............................................................................................... G7-1
Introduction ................................................................................................................. G7-1
Review of the Science .................................................................................................. G7-1
Overview of Questions Asked................................................................................................G7-1
Data Sources and Process Used to Answer Questions ...........................................................G7-2
Question 1. What Are the Associations Between Physical Activity and Incidence of
Specific Cancers? If an Association Exists, What Is the Dose-Response Pattern? ................G7-2
Question 2: What Are the Effects of Physical Activity on Cancer Survivors,
Including Late and Long-Term Effects of Treatment, Quality of Life, and
Prognosis? ............................................................................................................................G7-13
Question 3: What Mechanisms Explain the Associations Between Physical Activity
and Cancer? ..........................................................................................................................G7-18
Overall Summary and Conclusions ......................................................................... G7-21
Research Needs.......................................................................................................... G7-22
Reference List ............................................................................................................ G7-23
Part G. Section 8: Mental Health................................................................................... G8-1
Introduction ................................................................................................................. G8-1
Review of the Science .................................................................................................. G8-1
Overview of Questions Asked................................................................................................G8-1
Data Sources and Process Used to Answer Questions ...........................................................G8-2
Question 1: Is There an Association Between Physical Activity and Depression?................G8-2
Question 2. Is There an Association Between Physical Activity and Anxiety? ...................G8-13
Question 3: Is There an Association Between Physical Activity and Psychological
Distress and Well-Being? .....................................................................................................G8-20
Question 4: Is There an Association Between Physical Activity and Cognitive
Function and Dementia?.......................................................................................................G8-27
Question 5: Is There an Association Between Physical Activity and Sleep?.......................G8-32
Question 6: Is There an Association Between Physical Activity and Other Aspects
of Mental Health? .................................................................................................................G8-36
Question 7: Is There an Association Between Physical Activity and Adverse
Psychological Events? ..........................................................................................................G8-37
Question 8: What Mechanisms Can Plausibly Explain the Association Between
Physical Activity and Mental Health? ..................................................................................G8-38
Overall Summary and Conclusions ......................................................................... G8-39
Physical Activity Guidelines Advisory Committee Report ix
Contents
Research Needs.......................................................................................................... G8-40
Reference List ............................................................................................................ G8-41
Part G. Section 9: Youth................................................................................................. G9-1
Introduction ................................................................................................................. G9-1
Review of the Science .................................................................................................. G9-1
Overview of Questions Addressed .........................................................................................G9-1
Data Sources and Process Used to Answer the Questions .....................................................G9-2
Question 1: Is Physical Activity Significantly Related to Cardiorespiratory Fitness
Among Children and Adolescents? If So, Is There an Established Dose-Response
Pattern? Is the Relation Influenced by Age, Developmental Status, Sex,
Race/Ethnicity, or Socioeconomic Status?.............................................................................G9-3
Question 2: Is Physical Activity Significantly Related to Muscular Strength Among
Children and Adolescents? If So, Is There an Established Dose-Response Pattern?
Is the Relation Influenced by Age, Developmental Status, Sex, Race/Ethnicity, or
Socioeconomic Status?...........................................................................................................G9-5
Question 3: Is Physical Activity Significantly Related to Body Composition in
Children and Adolescents? If So, Is There an Established Dose-Response Pattern?
Is the Relation Influenced by Age, Developmental Status, Sex, Race/Ethnicity, or
Socioeconomic Status?...........................................................................................................G9-7
Question 4: Is Physical Activity Significantly Related to Cardiovascular and
Metabolic Health in Children and Adolescents? If So, Is There an Established
Dose-Response Pattern? Is the Relation Influenced by Age, Developmental Status,
Sex, Race/Ethnicity, or Socioeconomic Status?...................................................................G9-11
Question 5: Is Physical Activity Significantly Related to Bone Health in Children
and Adolescents? If So, Is There an Established Dose-Response Pattern? Is the
Relation Influenced by Age, Developmental Status, Sex, Race/Ethnicity, or
Socioeconomic Status?.........................................................................................................G9-14
Question 6: Is Physical Activity Significantly Related to Mental Health in Children
and Adolescents? If So, Is There an Established Dose-Response Pattern? Is the
Relation Influenced by Age, Developmental Status, Sex, Race/Ethnicity, or
Socioeconomic Status?.........................................................................................................G9-17
Overall Summary and Conclusions ......................................................................... G9-20
Research Needs.......................................................................................................... G9-21
Reference List ............................................................................................................ G9-22
Part G. Section 10: Adverse Events ............................................................................. G10-1
Introduction ............................................................................................................... G10-1
Review of the Science ................................................................................................ G10-3
Overview of the Questions Asked........................................................................................G10-3
Data Sources and Process Used To Answer Questions ........................................................G10-3
Question 1. What Types of Activities Have the Lowest Risk of Musculoskeletal
Injuries? ................................................................................................................................G10-4
Question 2. How Does the Dose of Physical Activity Affect the Risk of
Musculoskeletal Injury? .....................................................................................................G10-10
Physical Activity Guidelines Advisory Committee Report x
Contents
Question 3. Are Individuals at Increased Risk of Sudden Adverse Cardiac Events
When They Are Being Physically Active?.........................................................................G10-19
Question 4. What General Factors Influence the Risks of Musculoskeletal Injury
and Other Adverse Events Related to Physical Activity? ..................................................G10-27
Question 5. Do the Benefits of Regular Physical Activity Outweigh the Risks?...............G10-37
Overall Summary and Conclusions ....................................................................... G10-39
Research Needs........................................................................................................ G10-41
Reference List .......................................................................................................... G10-42
Part G. Section 11: Understudied Populations........................................................... G11-1
Introduction ............................................................................................................... G11-1
Review of the Science: Health Outcomes Associated With Physical
Activity in People With Disabilities ......................................................................... G11-2
Introduction ..........................................................................................................................G11-2
Overview of the Questions Asked........................................................................................G11-3
Data Sources and Process Used To Answer Questions ........................................................G11-4
Question 1. What Is the Evidence That Physical Activity Improves
Cardiorespiratory Fitness in People With Disabilities?........................................................G11-7
Question 2. What Is the Evidence That Physical Activity Improves Lipid Profiles
in People With Disabilities? .................................................................................................G11-8
Question 3. What Is the Evidence That Physical Activity Improves
Musculoskeletal Health in People With Disabilities? ..........................................................G11-9
Question 4. What Is the Evidence That Physical Activity Improves Functional
Health in People With Disabilities? ...................................................................................G11-12
Question 5. What Is the Evidence that Physical Activity Reduces Secondary
Conditions in People With Disabilities?.............................................................................G11-18
Question 6. What Is the Evidence That Physical Activity Helps Maintain Healthy
Weight and Improve Metabolic Health? ............................................................................G11-21
Question 7. What Is the Evidence That Physical Activity Improves Mental Health
in People With Disabilities? ...............................................................................................G11-23
Question 8. What Do We Know About the Safety of Exercise in People With
Disabilities? ........................................................................................................................G11-26
Overall Summary and Conclusions ....................................................................................G11-31
Research Needs ..................................................................................................................G11-34
Review of the Science: Physical Activity During Pregnancy and the
Postpartum Period .................................................................................................. G11-36
Introduction ........................................................................................................................G11-36
Overview of Questions Asked............................................................................................G11-37
Data Sources and Process Used To Answer Questions ......................................................G11-37
Question 1. What Does Recent Research Indicate About the Possible Risks of
Moderate- or Vigorous-Intensity Physical Activity by Women Who Are Pregnant? ........G11-38
Question 2. Does Being Physically Active While Pregnant Provide Any Health
Benefits?.............................................................................................................................G11-38
Physical Activity Guidelines Advisory Committee Report xi
Contents
Physical Activity Guidelines Advisory Committee Report xii
Question 3. Does Being Physically Active During the Postpartum Period Provide
Any Health Benefits? .........................................................................................................G11-39
Overall Summary and Conclusion......................................................................................G11-39
Review of the Scientific Evidence: Racial and Ethnic Diversity......................... G11-40
Introduction ........................................................................................................................G11-40
Overview of Questions Asked............................................................................................G11-42
Data Sources and Process Used To Answer Questions ......................................................G11-42
Question 1. Is There Evidence That the Physical Activity Dose for Improving
Health Should Vary by Race or Ethnicity? ........................................................................G11-42
Overall Summary and Conclusions ....................................................................................G11-45
Research Needs ..................................................................................................................G11-45
Reference List .......................................................................................................... G11-46
Part H: Research Recommendations............................................................................... H-1
Overarching Research Recommendations.................................................................. H-1
Research Recommendations of PAGAC Subcommittees .......................................... H-5
Physical Activity Guidelines Advisory Committee Subcommittee
Assignments .....................................................................................................Back Matter-1
Biographical Sketches of the 2008 Physical Activity Guidelines
Advisory Committee Members ......................................................................Back Matter-3
List of Figures
Figure D.1. The Relative Exercise Intensity for Walking at 3.0 mph
(3.3 METs) and 4.0 mph (5.0 METs) Expressed as a Percent of
VO2max for Adults With an Exercise Capacity Ranging from 4 to
14 METs.......................................................................................................D-7
Figure D.2. Estimated Age Adjusted Percentage of Persons ≥18 Years
Reported Meeting the Healthy People 2010 Objective for Regular
Physical Activity in 2001 and 2005: Data from BRFSS............................D-11
Figure D.3. Reported Physical Activity by Adults in the USA: 1997-2006 The
Healthy People 2010 Database...................................................................D-12
Figure D.4. Reported Physical Activity by Adults in the USA: 2001-2005
Data from BRFSS.......................................................................................D-13
Figure D.5. Percent of High School Students in the United States with Various
Physical Activity Profiles: 1999-2005 Data from YBRFSS ......................D-15
Figure F.1. Physical Activity Guidelines for Americans: Conceptual
Framework for Literature Review................................................................ F-2
Figure G1.1. Relative risks of all-cause mortality according to exercise and
nonexercise activities, Shanghai Women’s Health Study........................G1-13
Figure G1.2. Shape of the Dose-Response Curve: Relative Risks of All-Cause
Mortality by Physical Activity Level (Studies With at Least 5
Levels of Physical Activity) .....................................................................G1-19
Figure G1.3. “Median” Shape of the Dose-Response Curve ........................................G1-20
Figure G2.1 Relative Risk of CVD in Women — Walking Amount/Week ................G2-14
Figure G2.2. Effect Sizes Seen in Interventions in Which BAFMD Is Used as a
Vascular Health Biomarker ......................................................................G2-24
Figure G2.3. Changes in Peak VO2 by Exercise Group ................................................G2-30
Figure G2.4. Changes in Peak VO2 by Exercise Group and Ordered by Change .........G2-31
Figure G3.1. Summary of Cross-Sectional Physical Activity and Metabolic
Syndrome Studies Using Categories of Physical Activity That
Could Be Used To Examine Dose-Response.............................................G3-4
Figure G3.2. Data Prospectively Demonstrating That Both Higher Levels of
Physical Activity and Fitness Protect Against the Future
Development of Metabolic Syndrome .......................................................G3-5
Figure G3.3. Summary of Longitudinal Fitness and Metabolic Syndrome
Studies That Used Categories of Fitness To Examine DoseResponse Relations ....................................................................................G3-6
Physical Activity Guidelines Advisory Committee Report xiii
List of Figures
Figure G3.4. Physical Activity/Exercise and Macrovascular Risk Reduction in
Type 2 Diabetes........................................................................................G3-19
Figure G4.1. Differences in Body Mass Index Due to Level of Physical
Activity.......................................................................................................G4-5
Figure G4.2. Weight Loss Related to a Diet Intervention, an Exercise
Intervention, and a Diet + Exercise Intervention .......................................G4-7
Figure G5.1. Point Estimates of Relative Risk (± 95% Confidence Intervals) of
Hip Fracture From Studies That Examined Multiple Levels of
Physical Activity (Most Active Group Versus Least Active
Group) ........................................................................................................G5-6
Figure G6.1. Prospective Cohort Studies With Measurement of Mobility
Limitations .................................................................................................G6-8
Figure G6.2. Prospective Cohort Studies With Measures of ADL, IADL, and
Global Outcomes........................................................................................G6-9
Figure G6.3. Exercise Interventions To Prevent Falls in Older Adults.........................G6-18
Figure G7.1. Late and Long-Term Effects of Cancer Treatment That May Be
Positively Affected by Physical Activity .................................................G7-14
Figure G8.1a Depression Symptoms: Prospective Cohort Studies, 1995 Through
2007: Crude Odds.......................................................................................G8-5
Figure G8.1b Depression Symptoms: Prospective Cohort Studies, 1995 Through
2007: Adjusted Odds..................................................................................G8-6
Figure G8.2 Depression Symptoms: Randomized Controlled Trials, 1995
Through 2007 .............................................................................................G8-9
Figure G8.3 Depression Symptoms: Prospective Cohort Studies 1995 Through
2007: Dose Response ...............................................................................G8-11
Figure G8.4a Anxiety Symptoms: Randomized Controlled Trials of Healthy
Adults 1995 Through 2007 ......................................................................G8-17
Figure G8.4b. Anxiety Symptoms: Randomized Controlled Trials of Medical
Patients 1995 Through 2007 ....................................................................G8-18
Figure G8.5 Feelings of Distress/Well-Being: Prospective Cohort Studies,
1995 Through 2007: Crude and Adjusted Odds.......................................G8-22
Figure G8.6 Feelings of Distress/Well-Being: Randomized Controlled Trials
1995 Through 2007 ..................................................................................G8-24
Figure G8.7 Feelings of Distress/Well-Being: Prospective Cohort Studies 1995
Through 2007: Dose Response ................................................................G8-26
Figure G8.8 Incident Total Dementia or Alzheimer’s Disease: Prospective
Cohort Studies, 1995 Through 2007: Crude and Adjusted Hazard..........G8-29
Figure G8.9 Physical Activity and Symptoms of Disrupted or Insufficient
Sleep: 13 Cross-Sectional Studies (Total n=84,904) ...............................G8-34
Physical Activity Guidelines Advisory Committee Report xiv
List of Figures
Physical Activity Guidelines Advisory Committee Report xv
Figure G10.1. Percentage of Recreational Runners or Walkers Injured by
Average Number of Miles Run per Week..............................................G10-12
Figure G10.2. Hours of Drill per Marching Plus General Conditioning (Solid
Line, Left Axis) and Injuries per 100 Recruits (Dotted Line, Right
Axis) by Week of Training.....................................................................G10-15
Figure G10.3. Rate or Odds Ratio for Injury Among Military Recruits During
Basic Training by Aerobic Fitness at Entry ...........................................G10-16
Figure G10.4. Risk of Sudden Adverse Cardiac Event by Level of Activity ................G10-20
Figure G10.5. Risk of Cardiac Arrest During Vigorous Activity and at Rest by
Usual Level of Activity ..........................................................................G10-22
Figure G10.6. Risk of Cardiac Arrest During Activity and at Rest by Usual Level
of Activity ..............................................................................................G10-24
Figure G11.1. Number of Articles Identified by Disability Group and Design
(N=139) ....................................................................................................G11-6
List of Tables
Table D.1. Classification of Physical Activity Intensity................................................D-3
Table D.2. Physical Activities Listed as 6.0 METs in the Compendium of
Physical Activities........................................................................................D-5
Table D.3. Walk, Jog, and Run Speeds and METs, MET-Minutes, METHours, and Distance (miles) for 2.5 Hours (150 min) and 5.0
Hours (300 min) per Week of Physical Activity. Also Listed Are
the Estimated Kilocalories (kcal) Expended by a 75 kg (165 lb)
Adult During 150 and 300 Minutes per Week at the Different
Intensities of Activity. ..................................................................................D-8
Table E.1. Process for Summarizing the Science ..........................................................E-2
Table G1.1. Minimum Amounts of Physical Activity Associated With
Significantly Lower Risks of All-Cause Mortality ....................................G1-6
Table G1.2. Walking and All-Cause Mortality ..............................................................G1-8
Table G2.1. Summary of Prospective Cohort Studies and Case-Control Studies
Published in the English Language Since 1996 Reporting on the
Relation Between Habitual Physical Activity and the Prevention
of Coronary Heart Disease, Cardiovascular Disease, or Stroke.................G2-7
Table G2.2. Table of Baseline Characteristics, Exercise Prescriptions, Training
Programs, and Outcome Measures in Two Randomized
Controlled Aerobic Exercise Training Studies.........................................G2-36
Table G5.1. Studies Examining the Association Between Participation in
Walking and Risk of Hip/Knee Osteoarthritis .........................................G5-19
Table G5.2. Select Individual Sports and Recreational Activities That Have
Been Associated With the Development of Osteoarthritis in at
Least One Study .......................................................................................G5-20
Table G5.3. Summary Descriptive Characteristics of the Randomized
Controlled Trials of Exercise Among Persons With Arthritis or
Other Rheumatic Conditions....................................................................G5-26
Table G10.1. Factors Associated With the Risk of Activity-Associated Adverse
Events .......................................................................................................G10-2
Table G10.2. Injuries per 1,000 Hours of Participation and Per 1,000
Participants by Activity, Finland (12) ......................................................G10-5
Table G10.3. Game and Practice Injury Rates* for Collegiate Sports
(Nationwide, 1988-2004),(18;19) High School Sports
(Nationwide, 1995-1997), (20) and Children’s Community
Organized Sports (Pittsburgh, 1999-2000) (21) .......................................G10-8
Table G10.4. Absolute Intensity by Age Group and Relative (Perceived)
Intensity (80) ..........................................................................................G10-23
Physical Activity Guidelines Advisory Committee Report xvii
List of Tables
Physical Activity Guidelines Advisory Committee Report xviii
Table G10.5. Annual Incidence* of Self-Reported Injury Requiring Medical
Advice by Age Group and Leisure-Time Physical Activity Level
(9) ...........................................................................................................G10-28
Table G10.6. Rate or Odds Ratio of Medically Attended Injury of Any Cause,
by BMI Category....................................................................................G10-32
Table G10.7. Safety Tips to Avoid Becoming Victim of Crime, Avoid Traffic
Injuries, or Minimize the Effects of Either* ..........................................G10-35
Table G10.8. Medical Expenditures for Active Versus Inactive Persons ....................G10-38
Table G11.1. Healthy People 2010 (HP 2010) Goals for Increasing Physical
Activity in Adults .....................................................................................G11-2
Table G11.2. Categories of Disability............................................................................G11-3
Table G11.3. Physical Activity and Cardiorespiratory Fitness in People With
Disabilities................................................................................................G11-7
Table G11.4. Physical Activity and Lipid Profiles in People With Disabilities ............G11-9
Table G11.5. Physical Activity and Muscle Strength in People With Disabilities ......G11-11
Table G11.6. Physical Activity and Flexibility in People With Disabilities................G11-12
Table G11.7. Physical Activity and Walking Speed in People With Disabilities........G11-13
Table G11.8. Physical Activity and Walking Distance in People With
Disabilities..............................................................................................G11-14
Table G11.9. Physical Activity and Quality of Life in People With Disabilities ........G11-15
Table G11.10. Physical Activity and Functional Independence in People With
Disabilities..............................................................................................G11-17
Table G11.11. Physical Activity and Balance in People With Disabilities ...................G11-18
Table G11.12. Physical Activity and Fatigue Reduction in People With
Disabilities..............................................................................................G11-19
Table G11.13. Physical Activity and Pain Reduction in People With Disabilities........G11-20
Table G11.14. Physical Activity and Body Composition in People With
Disabilities..............................................................................................G11-22
Table G11.15. Physical Activity and Depression in People With Disabilities ..............G11-23
Table G11.16. Physical Activity and Other Major Mental Health Outcomes in
People With Disabilities.........................................................................G11-24
Table G11.17. Number and Percentage of Subjects With Adverse Events by
Seriousness of Event and Exposure Group ............................................G11-27
Table G11.18. Classification, Number, and Percentage of Serious/Non-Serious
Adverse Events in Exercise and Control Groups ...................................G11-27
Table G11.19. Summary Table on Level of Evidence by Health Outcome
Aggregated by Physical and Cognitive Disabilities ...............................G11-32
Membership Lists
Physical Activity Guidelines Advisory Committee Members
Chair
William L. Haskell, PhD
Stanford Prevention Research Center
Stanford University School of Medicine
Stanford, CA
Vice Chair
Miriam E. Nelson, PhD
John Hancock Center for Physical Activity and Nutrition
Friedman School of Nutrition Science and Policy
Tufts University
Boston, MA
Rod K. Dishman, PhD
Biomedical and Health Sciences Institute
Department of Kinesiology
College of Education
The University of Georgia
Athens, GA
Edward T. Howley, PhD
Center for Physical Activity and Health
Department of Exercise, Sport and Leisure
Studies
College of Education, Health, and Human
Sciences
University of Tennessee
Knoxville, TN
Wendy M. Kohrt, PhD
Division of Geriatric Medicine
Department of Medicine
University of Colorado Denver
Denver, CO
William E. Kraus, MD
Division of Cardiovascular Medicine
Department of Medicine
Duke University School of Medicine
Durham, NC
I-Min Lee, MBBS, ScD
Division of Preventive Medicine
Brigham and Women's Hospital and Harvard
Medical School
Department of Epidemiology
Harvard School of Public Health
Boston, MA
Anne McTiernan, MD, PhD
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
Seattle, WA
Russell R. Pate, PhD
Department of Exercise Science
Arnold School of Public Health
University of South Carolina
Columbia, SC
Kenneth E. Powell, MD, MPH
Public Health and Epidemiologic Consultant
Atlanta, GA
Judith G. Regensteiner, PhD
General Internal Medicine and Cardiology
Center for Women's Health Research
School of Medicine
University of Colorado Denver
Denver, CO
James H. Rimmer, PhD
National Center on Physical Activity and
Disability and Rehabilitation
Department of Disability and Human
Development
University of Illinois at Chicago
Chicago, IL
Antronette K. (Toni) Yancey, MD, MPH
Department of Health Services and
Center to Eliminate Health Disparities
UCLA School of Public Health
Los Angeles, CA
Physical Activity Guidelines Advisory Committee Report Front Matter–1
Membership Lists
Consultants to Advisory Committee Subcommittees
Jason D. Allen, PhD
Duke University Medical Center
Steven N. Blair, PED
University of South Carolina
David M. Buchner, MD, MPH
National Center for Chronic Disease Prevention and Health Promotion
Center for Disease Prevention and Health Promotion
Centers for Disease Control and Prevention (CDC)
A. John Campbell, MD
University of Otago, Dunedin, New Zealand
Timothy Church, MD, MPH, PhD
Pennington Biomedical Research Center
Stephen R. Daniels, MD
University of Colorado School of Medicine
Loretta DiPietro, PhD, MPH
Yale University School of Medicine
Joseph E. Donnelly, EdD
University of Kansas
Brian D. Duscha, MS
Duke University Medical Center
Christina D. Economos, PhD
Tufts University
Roger Fielding, PhD
Tufts University
Julie Gilchrist, MD
National Center for Injury Prevention and Control, CDC
Jack Guralnik, MD, PhD
National Institute of Aging, National Institutes of Health
Bernard (Bob) Gutin, PhD
University of North Carolina at Chapel Hill
Steven M. Haffner, MD
University of Texas Health Science Center at San Antonio
Richard F. Hamman, MD, DrPH
University of Colorado Denver
Physical Activity Guidelines Advisory Committee Report Front Matter–2
Membership Lists
Jennifer Hootman, PhD
National Center for Chronic Disease Prevention and Health Promotion, CDC
Amy G. Huebschman, MD
University of Colorado Denver
John M. Jakicic, PhD
University of Pittsburgh
Bruce Jones, MD, MPH
US Army Center for Health Promotion and Preventive Medicine
George A. Kelley, DA
West Virginia University
Harold W. (Bill) Kohl III, PhD
National Center for Chronic Disease Prevention and Health Promotion, CDC; and University of
Texas Health Science Center at Houston, School of Public Health
Shiriki Kumanyika, PhD, MPH
University of Pennsylvania
Nancy E. Lane, MD
University of California Davis Medical Center
Caroline A. Macera, PhD
San Diego State University
Robert M. Malina, PhD
Tarleton State University
JoAnn Manson, MD, DrPH, MPH
Harvard University School of Public Health
Patrick J. O’Connor, PhD
University of Georgia
James M. Pivarnik, PhD
Michigan State University
Irene Schauer, MD, PhD
University of Colorado Denver
Kathryn H. Schmitz, PhD, MPH
University of Pennsylvania School of Medicine
Anita Stewart, PhD
University of California, San Francisco
Paul D. Thompson, MD
University of Connecticut, Hartford Hospital
Phillip D. Tomporowski, PhD
University of Georgia
Physical Activity Guidelines Advisory Committee Report Front Matter–3
Membership Lists
Physical Activity Guidelines Advisory Committee Report Front Matter–4
US Department of Health and Human Services Staff
Physical Activity Guidelines Steering Committee
Penelope Slade Royall, PT, MSW
Deputy Assistant Secretary for Health (Disease Prevention and Health Promotion)
Rear Admiral, US Public Health Service
Director, Secretary’s Prevention Priority
Richard P. Troiano, PhD
Captain, US Public Health Service
Office of Disease Prevention and Health Promotion
Physical Activity Guidelines Coordinator and Advisory Committee Executive Secretary
Melissa A. Johnson, MS
Executive Director, President’s Council on Physical Fitness and Sports
Physical Activity Outreach Coordinator
Harold W. (Bill) Kohl III, PhD
Epidemiology and Surveillance Team Leader
Physical Activity and Health Branch, CDC
Physical Activity Science Coordinator (until January 2008)
Janet E. Fulton, PhD
Epidemiology and Surveillance Team Leader (Acting)
Physical Activity and Health Branch, CDC
Physical Activity Science Coordinator (beginning January 2008)
CDC Physical Activity Guidelines Scientific Database Management Staff
Heidi M. Blanck, PhD
Commander, US Public Health Service
David R. Brown, PhD
David M. Buchner, MD, MPH
Susan A. Carlson, MPH
Carl J. Caspersen, PhD, MPH
Jacqueline N. Epping, MEd
Janet E. Fulton, PhD
Patrick Glew, MPH
C. Dexter (Bo) Kimsey, PhD
Captain, US Public Health Service
Harold W. (Bill) Kohl III, PhD
L. Michele Maynard, PhD
Candace D. Rutt, PhD
Jesus Soares, MSc, ScD
Linda K. West, MSPH
Commander, US Public Health Service
Membership Lists
Database and Report Information Specialist
Reba A. Norman, MLM
National Center for Chronic Disease Prevention and Health Promotion, CDC
Physical Activity Guidelines Management Staff
Christopher W. Barrett, PT, DPT
Lieutenant, US Public Health Service
Office of Disease Prevention and Health Promotion
Christy Choi
Office of Disease Prevention and Health Promotion
Tynetta Dreher
President’s Council on Physical Fitness and Sports
Yolande Gary
Office of Disease Prevention and Health Promotion
Sarah Linde-Feucht, MD
Captain, US Public Health Service
Office of Disease Prevention and Health Promotion
Marian Robinson
Office of Health Policy
Office of the Assistant Secretary for Planning and Evaluation
Sandra Saunders
Office of Disease Prevention and Health Promotion
Wilma M. Tilson, MPH
Office of Health Policy
Office of the Assistant Secretary for Planning and Evaluation
Eduardo Valdivia
Office of Health Policy
Office of the Assistant Secretary for Planning and Evaluation
Jennifer Tucker, MPA
National Center for Chronic Disease Prevention and Health Promotion, CDC
With assistance from interns and fellows:
Susan Bishop
Tamyra Carroll Garcia, MPH
Elaina Filauro
Scott Galla
Neela Patel, MD, MPH
Physical Activity Guidelines Advisory Committee Report Front Matter–5
Technical Writer/Editor
Anne Brown Rodgers
Technical assistance to the subcommittees in preparing the report was provided by the
following individuals:
Pamela Andrews, MS University of Tennessee
Ming-De Chen, OT, MOE University of Illinois at Chicago
Matthew Herring, MS University of Georgia
Mary A. Kennedy, MS Tufts University
Frithjof Müller, MS University of Konstanz, Konstanz, Germany
Jennifer O'Neill, MPH University of South Carolina
Rebecca M. Speck, MPH University of Pennsylvania School of Medicine
Kathleen Y. Wolin, ScD Washington University School of Medicine
Physical Activity Guidelines Advisory Committee Report Front Matter–6
Part A:
Executive Summary
Disease prevention and health promotion are high priority features of President George W.
Bush’s Healthier US initiative and Secretary of Health and Human Services (HHS)
Michael O. Leavitt’s Prevention Priority. Getting routine medical screenings, making
healthy choices and avoiding risks, eating a nutritious diet, and being physically active are
major components of chronic disease prevention. On October 27, 2006, Secretary Leavitt
announced plans for the development of Federal Physical Activity Guidelines for Americans
to be issued in 2008. These Federal guidelines will serve as the benchmark and single,
authoritative voice for providing science-based guidance on physical activity, fitness, and
health for Americans. In preparation for the development by HHS of these guidelines, an
important first step was to conduct a comprehensive review and analysis of the scientific
literature on physical activity and health published since 1995. This task was assigned to the
Physical Activity Guidelines Advisory Committee (PAGAC).
The Physical Activity Guidelines Advisory
Committee
Following the announcement by the HHS Secretary of plans to develop physical activity
guidelines, nominations for membership on the PAGAC were solicited through the
Federal Register. PAGAC members were expected to be respected and published experts in
the science of physical activity and its role in health promotion and disease prevention; be
familiar with the purpose, communication, and application of Federal guidelines; not be
employees of the Federal Government; and be free of any commercial conflicts of interest.
In February 2007, the Secretary of HHS appointed 13 members to the PAGAC, including a
chair and vice-chair. Secretary Leavitt’s charge to the PAGAC was to review existing
scientific literature to identify where there is sufficient evidence to develop a comprehensive
set of specific physical activity recommendations and identify areas where further scientific
research is needed. The intent of HHS is to develop physical activity recommendations for
all Americans that will be tailored as necessary for specific subgroups of the population.
PAGAC was not to prepare guidelines or policy statements. This report is the result of work
by the Committee, consultants to the Committee, and HHS support staff. Names and
affiliations of PAGAC members, consultants, and HHS support staff are listed at the
beginning of this report.
Initially, the PAGAC formed 9 subcommittees, focused on the 9 health outcomes identified
by the CDC team assigned to assist the PAGAC: all-cause mortality, cardiorespiratory
health, metabolic health, energy balance, musculoskeletal health, functional health, cancer,
mental health, and adverse events. PAGAC members then added 2 other subcommittees:
Physical Activity Guidelines Advisory Committee Report A–1
Part A. Report Summary
youth and understudied populations (i.e., populations not covered in other chapters —
persons with disabilities, women during pregnancy and the postpartum period, and races and
ethnicities other than non-Hispanic white). The conclusions in this report represent the
consensus of the entire PAGAC.
Report Contents
This report includes 3 major components. The first provides an introduction to the PAGAC
process; definition of key terms used in the report; background information on dose
response, recent trends in physical activity among Americans, and an overview of physical
activity guidelines development in the United States; a summary and integration of the
science reviewed by PAGAC; and an explanation of the development and use of the
Physical Activity Guidelines for Americans Scientific Database. The second component
includes 11 sections that review and summarize the scientific literature relating physical
activity to individual health outcomes. The third component provides a summary of the
PAGAC’s collective recommendations for future research. References cited are at the end of
each section.
Review of the Science on Physical Activity and
Health
One of the PAGAC’s major goals was to integrate the scientific information on the relation
between physical activity and health and to summarize it in a manner that could be used
effectively by HHS personnel to develop the Physical Activity Guidelines for Americans and
related policy statements. The resulting consensus statements based on the evidence relating
physical activity to health are provided in Part E: Integration and Summary of the Science
and the conclusions in each of the chapters in Part G: The Science Base. A number of the
key conclusions by the PAGAC, based on their review of the scientific literature, are
summarized below.
Overall Benefits of Physical Activity on Health
Very strong scientific evidence based on a wide range of well-conducted studies shows that
physically active people have higher levels of health-related fitness, a lower risk profile for
developing a number of disabling medical conditions, and lower rates of various chronic
diseases than do people who are inactive.
Children and Youth
Strong evidence demonstrates that the physical fitness and health status of children and
youth are substantially enhanced by frequent physical activity. Compared to inactive young
people, physically active children and youth have higher levels of cardiorespiratory
endurance and muscular strength, and well-documented health benefits include reduced
Physical Activity Guidelines Advisory Committee Report A–2
Part A. Report Summary
body fatness, more favorable cardiovascular and metabolic disease risk profiles, enhanced
bone health, and reduced symptoms of anxiety and depression.
Adults and Older Adults
Strong evidence demonstrates that, compared to less active persons, more active men and
women have lower rates of all-cause mortality, coronary heart disease, high blood pressure,
stroke, type 2 diabetes, metabolic syndrome, colon cancer, breast cancer, and depression.
Strong evidence also supports the conclusion that, compared to less active people, physically
active adults and older adults exhibit a higher level of cardiorespiratory and muscular
fitness, have a healthier body mass and composition, and a biomarker profile that is more
favorable for preventing cardiovascular disease and type 2 diabetes and for enhancing bone
health. Modest evidence indicates that physically active adults and older adults have better
quality sleep and health-related quality of life.
Older Adults
In addition to those benefits listed above, strong evidence indicates that being physically
active is associated with higher levels of functional health, a lower risk of falling, and better
cognitive function.
Women During Pregnancy and the Postpartum Period
Strong evidence indicates that moderate-intensity physical activity during pregnancy by
generally healthy women increases cardiorespiratory and metabolic fitness without
increasing the risk of low birth weight, preterm delivery, or early pregnancy loss. Moderateintensity physical activity during the postpartum period does not appear to adversely affect
milk volume or composition or infant growth. Physical activity alone does not produce
weight loss in postpartum women except when combined with dietary changes.
Persons With Disabilities
For many physical and cognitive disabilities, scientific evidence for various health and
fitness outcomes is still limited due to the lack of research. Moderate to strong evidence
indicates that increases in aerobic exercise improve cardiorespiratory fitness in individuals
with lower limb loss, multiple sclerosis, stroke, spinal cord injury, and mental illness.
Limited data show similar results for people with cerebral palsy, muscular dystrophy, and
Alzheimer’s disease. Moderate to strong evidence also exists for improvements in walking
speed and walking distance in patients with stroke, multiple sclerosis, and intellectual
disabilities. Moderately strong evidence indicates that resistance exercise training improves
muscular strength in persons with such conditions as stroke, multiple sclerosis, cerebral
palsy, spinal cord injury, and intellectual disability. Although evidence of benefit is
suggestive for such outcomes as flexibility, atherogenic lipids, bone mineral density, and
quality of life, the data are still very limited.
Physical Activity Guidelines Advisory Committee Report A–3
Part A. Report Summary
Racial and Ethnic Diversity
Only a limited number of prospective observational or experimental studies investigating the
relation between physical activity and health outcomes have had adequate samples of nonHispanic white men or women and one or more other race/ethnicities to allow a direct
comparison of benefits. However, in the few studies where direct comparisons have been
made, no meaningful difference appears to exist, and studies conducted in other countries
with race-ethnic populations other than non-Hispanic white report similar results. Thus,
based on the currently available scientific evidence, the dose of physical activity that
provides various favorable health and fitness outcomes appears to be similar for adults of
various races and ethnicities.
Persons Who Are Overweight or Obese
Strong evidence shows that physically active adults who are overweight or obese experience
a variety of health benefits that are generally similar to those observed in people of optimal
body weight (body mass index [BMI] = 18.5-24.9). These benefits include lower rates of allcause mortality, coronary heart disease, hypertension, stroke, type 2 diabetes, colon cancer,
and breast cancer. Some of these benefits appear to be independent of a loss in body weight,
while in some cases weight loss in conjunction with an increase in physical activity results
in even greater benefits. Because of the health benefits of physical activity that are
independent of body weight classification, adults of all sizes and shapes gain health and
fitness benefits by being habitually physically active.
Patterns of Physical Activity Associated With Better Health and
Fitness
PAGAC members recognized that, when considering the intensity of an activity, it is most
appropriate scientifically to express the intensity relative to a person’s capacity (relative
intensity). However, the PAGAC also recognized that communicating to the public the
process of determining relative intensity is difficult and that intensity expressed in absolute
terms is a reasonable alternative. Table D.1 and Figure D.1 located in Part D: Background
provide information on the relation between absolute and relative intensity. Also, the
committee concluded that, when classifying activities by intensity using metabolic
equivalents (METs), the appropriate classification of moderate-intensity activity is 3.0 to
5.9 rather than 3.0 to 6.0 METs and vigorous intensity is 6.0 or greater METs (Table D.2).
Based on the existing science, it is not possible to be highly precise in selecting a single
expression of activity amount that provides improved health because of the diversity in the
types of physical activity reported and the conditions under which they are performed, the
different questionnaires used to assess these activities, and the various units of measurement
used to express the characteristics of the activity. Also, the baseline activity and fitness
levels of the population and the targeted health outcomes influence the effective dose. The
committee constructed a table to assist in translating the different units of measurements for
Physical Activity Guidelines Advisory Committee Report A–4
Part A. Report Summary
the amount of activity performed for a range of activity intensities performed for 150 and
300 minutes per week (2.5 and 5 hours per week) (Table D.3).
Children and Youth
Few studies have provided data on the dose response for various health and fitness outcomes
in children and youth. However, substantial data indicate that important health and fitness
benefits can be expected to accrue to most children and youth who participate daily in 60 or
more minutes of moderate to vigorous physical activity. Certain specific types of physical
activity should be included in an overall physical activity pattern in order for children and
youth to gain comprehensive health benefits. These include regular participation in each of
the following types of physical activity on 3 or more days per week: resistance exercise to
enhance muscular strength in the large muscle groups of the trunk and limbs, vigorous
aerobic exercise to improve cardiorespiratory fitness and cardiovascular and metabolic
disease risk factors, and weight-loading activities to promote bone health. Experiences
consistent with these goals involve participation in physical activities that are
developmentally appropriate, that minimize the potential risks of overtraining and injuries,
and that provide children and youth with opportunities for enjoyable participation in a wide
range of specific forms of physical activity.
Adults and Older Adults
Data from a large number of studies evaluating a wide variety of benefits in diverse
populations generally support 30 to 60 minutes per day of moderate to vigorous intensity
physical activity on 5 or more days of the week. For a number of benefits, such as lower risk
for all-cause mortality, coronary heart disease, stroke, hypertension, and type 2 diabetes in
adults and older adults, lower risk is consistently observed at 2.5 hours per week (equivalent
to 30 minutes per day, 5 days per week) of moderate to vigorous intensity activity. The
amount of moderate to vigorous intensity activity most consistently associated with
significantly lower rates of colon and breast cancer and the prevention of unhealthy weight
gain or significant weight loss by physical activity alone is in the range of 3 to 5 hours per
week.
It is possible to combine aerobic activities of different types and intensities into a single
measure of amount of activity. For many studies, the amount of moderate and vigorous
intensity activity associated with significantly lower rates of disease or improvements in
biomarkers and fitness is in the range of 500 to 1,000 MET-minutes per week. An adult can
achieve a target of 500 MET-minutes per week by walking at about 3.0 miles per hour for
approximately 150 minutes per week (7.5 miles), walking faster at 4.0 miles per hour for
100 minutes (6.6 miles), or jogging or running at 6 miles per hour for about 50 minutes per
week (5.0 miles). To achieve 1,000 MET-minutes per week, these amounts of activity would
need to be doubled. For an explanation of the use of METs and MET-minutes for calculating
the amount of activity see Part D: Background, especially Table D.2 and its associated text.
Physical Activity Guidelines Advisory Committee Report A–5
Part A. Report Summary
Resistance or muscle-strengthening exercises are important for maintaining muscle and
bone health, and these exercises enhance functional status and contribute to a reduction of
falls in older adults. Most of the evidence supports a resistance activity program with the
following characteristics: progressive muscle strengthening exercises that target all major
muscle groups performed on 2 or more days per week. To enhance muscle strength, 8 to
12 repetitions of each exercise should be performed to volitional fatigue. One set is
effective; however, limited evidence suggests that 2 or 3 sets may be more effective.
Older Adults
If a person has a low exercise capacity (physical fitness), the intensity and amount of
activity needed to achieve many health-related and fitness benefits are less than for someone
who has a higher level of activity and fitness. Because the exercise capacity of adults tends
to decrease as they age, older adults generally have lower exercise capacities than younger
persons. Thus, they need a physical activity plan that is of lower absolute intensity and
amount (but similar in relative intensity and amount) than is appropriate for more fit people,
especially when they have been sedentary and are starting an activity program.
Older Adults at Risk of Falls
For older adults at risk of falling, strong evidence exists that regular physical activity is safe
and reduces falls by about 30%. Most evidence supports a program of exercise with the
following characteristics: 3 times per week of balance training and moderate-intensity
muscle-strengthening activities for 30 minutes per session, with additional encouragement to
participate in moderate-intensity walking activities 2 or more times per week for 30 minutes
per session. Some evidence, albeit less consistent, suggests that tai chi exercises also reduce
falls. There is no evidence that planned physical activity reduces falls in adults and older
adults who are not at risk of falls.
Persons With Disabilities
For a majority of the studies reviewed involving persons with disabilities, the exercise
regimen followed was that currently recommended for the general public — aerobic
exercise of 30 to 60 minutes, 3 to 5 days per week at moderate intensity, and resistance
training with 1 or 2 sets of 8 to 12 repetitions using appropriate muscle groups 2 to 3 times
per week. Although other activity regimens might be effective, they have not been
adequately evaluated.
Persons Achieving Weight Stability
The optimal amount of physical activity needed for weight maintenance (defined as less than
3% change in body weight) over the long-term is unclear. However, the evidence is clear
that physical activity provides benefit for weight stability. A great deal of inter-individual
variability exists with physical activity and weight stability, and many persons may need
more than 150 minutes of moderate-intensity activity per week to maintain their weight at a
Physical Activity Guidelines Advisory Committee Report A–6
Part A. Report Summary
stable level. Data from recent well-designed randomized controlled trials lasting up to 12
months indicate that aerobic physical activity performed to achieve 13 to 26 MET-hours per
week is associated with approximately a 1% to 3% weight loss (i.e., an amount generally
considered to represent weight stability). Thirteen MET-hours per week is approximately
equivalent to walking at 4 miles per hour for 150 minutes per week or jogging at 6 miles per
hour for 75 minutes per week.
Persons Achieving Weight Loss
A wide range of studies provides evidence of a dose-response relation between physical
activity and weight loss. Clear, consistent data show that a large volume of physical activity
is needed for weight loss in the absence of concurrent dietary changes. The physical activity
equivalent of 26 kilocalories per kilogram of body weight (1,560 MET-minutes) or more per
week is needed for weight loss of 5% or greater. Smaller amounts of weight loss are seen
with smaller amounts of physical activity. This relatively high volume of physical activity is
equivalent to walking about 45 minutes per day at 4 miles per hour or about 70 minutes per
day at 3 miles per hour, or jogging 22 minutes per day at 6 miles per hour.
The role of energy intake (diet) must be considered in any discussion of weight control.
When calorie intake is carefully controlled at a baseline level, the magnitude of any weight
loss is what would be expected given the energy expenditure of the person’s physical
activity. However, in situations in which people’s dietary intake is not controlled, the
amount of weight loss due to the increase in physical activity is not commensurate to what
would be expected. Therefore, for most people to achieve substantial weight loss (i.e., more
than 5% decrease in body weight), a dietary intervention also is needed. The dietary
intervention could include either maintenance of baseline caloric intake, or a reduction in
caloric intake to accompany the physical activity intervention. The magnitude of change in
weight due to physical activity is additive to that associated with caloric restriction.
Persons Achieving Weight Maintenance After Weight Loss
The scientific evidence for the effectiveness of physical activity alone in preventing weight
regain following significant weight loss is limited. Available data indicate that to prevent
substantial weight regain over 6 months or longer, many adults need to exercise in the range
of 60 minutes of walking or 30 minutes of jogging daily (approximately 4.4 kilocalories per
kilogram per day of activity energy expenditure). The literature generally supports the
concept that “more is better” for long-term weight maintenance following weight loss.
Further, the evidence indicates that individuals who are successful at long-term weight
maintenance appear to limit caloric intake in addition to maintaining physical activity.
Physical Activity Guidelines Advisory Committee Report A–7
Part A. Report Summary
Special Considerations Related to the Pattern of Physical Activity
and Health
The following section presents additional findings from the Committee’s review of the
literature. These findings represent important considerations for developing comprehensive
physical activity guidelines for Americans.
Some Physical Activity Is Better Than None
The least active people in the population generally have the highest risk of a variety of
negative health outcomes. Although the minimum amount of physical activity needed to
decrease this risk is not clear, increasing evidence suggests that participating in no more than
1 hour per week of moderate-intensity physical activity is associated with lower risk of allcause mortality and the incidence of coronary heart disease. At this lower amount and
intensity of activity, the benefits usually are less than that observed with greater amounts of
activity, and studies are much less consistent about the nature and magnitude of these
benefits. Nevertheless, the dose-response curves for the major health benefits clearly
indicate an inverse relation between the dose of activity and rate of disease. Although the
minimum amount of activity needed to produce a benefit cannot be stated with certainty,
nothing would suggest a threshold below which there are no benefits.
Additional Health Benefits With More Physical Activity
Reasonably strong evidence demonstrates that participating in moderate to vigorous physical
activity for more than 150 minutes per week is associated with greater health benefits for a
variety of health outcomes, including chronic disease prevention, improvement of various
disease biomarkers, and the maintenance of a healthy weight. However, in a number of
studies where such a dose response is observed in preventing chronic disease or reducing
all-cause mortality, the relation appears to be curvilinear. This means that the absolute
increase in benefits becomes less and less for any given increase in the amount of physical
activity.
Additional Benefits With Vigorous Physical Activity
Strong evidence indicates that an increase in intensity is associated with greater
improvements for some health outcomes compared to those observed with moderateintensity activity. This is especially true for outcomes related to fitness. However, it should
be noted that an increase in intensity was often associated with an increase in volume of
activity for many observational and experimental studies, and it is difficult to separate the
benefits of each.
Frequency of Physical Activity
Very limited published research has systematically evaluated health or fitness benefits in
response to different frequencies of activity sessions per week when the amount of activity
Physical Activity Guidelines Advisory Committee Report A–8
Part A. Report Summary
is held reasonably constant. Although the data are limited, the results suggest that for health
and fitness benefits, the frequency of activity is much less important than the amount or
intensity. Many experimental studies since 1995 have demonstrated beneficial effects of 120
to 150 minutes per week of moderate- or vigorous-intensity activity, usually performed
during 3 to 5 sessions per week, so we know that this frequency of activity is effective. Only
limited data are available comparing the benefits from just 1 or 2 sessions per week with
multiple sessions spread throughout the week with activity amount and intensity held
constant.
Accumulation of Physical Activity
The concept of accumulation refers to performing multiple short bouts of physical activity
throughout the day. Some scientific evidence of moderate strength suggests that
accumulating 30 or more minutes of moderate- to vigorous-intensity aerobic activity
throughout the day in bouts of 10 minutes or longer produces improvements in
cardiorespiratory fitness. Limited data indicate that accumulated short bouts of 8 to 10
minutes improve selected biomarkers for cardiovascular disease in a manner generally
similar to that observed when activity of a similar amount and intensity is performed in a
single bout of 30 or more minutes. Data on the effects of accumulating activity involving
multiple short bouts for the prevention of major clinical outcomes, such as all-cause
mortality, cardiovascular disease, diabetes, and selected cancers, are very limited due to the
type of data collected from the questionnaires in most prospective observational studies. In
these studies, people are generally asked about the total amount of physical activity
performed, and it has not been possible to precisely differentiate between activities
conducted in a single, long bout versus those conducted in multiple, short bouts over the
day.
Health Benefits of Brisk Walking
Strong evidence shows that a regimen of brisk walking provides a number of health and
fitness benefits for adults and older adults, including lower risk of all-cause mortality,
cardiovascular disease, and type 2 diabetes. Some evidence is available indicating that
walking at faster pace is associated with greater health benefits than walking at a slower
pace. Strong evidence also shows that frequent bouts of walking increase cardiorespiratory
and metabolic fitness, especially in people who have been performing little activity on a
regular basis. Limited to moderate evidence suggests that walking helps to maintain bone
density and reduce fractures over time, especially in women, and helps to maintain joint
health and functional ability in adults and older adults.
Safety and Adverse Events
Activity-related adverse events such as musculoskeletal injuries are common but are usually
mild, especially for moderate intensity activities such as walking. Overall, the health
benefits of regular physical activity outweigh the risks. Much of the research that has
addressed adverse events during physical activity has evaluated the risk of musculoskeletal
Physical Activity Guidelines Advisory Committee Report A–9
Part A. Report Summary
Physical Activity Guidelines Advisory Committee Report A–10
injuries or sudden cardiac death during vigorous physical activity (e.g., jogging, running,
competitive sports, military training). Few well-conducted studies are available evaluating
risk during moderate-intensity activity intended primarily to improve health. Injury rates are
higher for collision and contact sports than for activities with fewer and less forceful contact
with other people or objects. Walking for exercise, gardening or yard work, dancing,
swimming, and golf are activities with the lowest injury rates. Injuries are more likely to
happen when people are more physically active than usual, and the risk is related to the size
of the increase. A series of small increments in physical activity, each followed by a period
of adaptation, is associated with lower rates of musculoskeletal injuries than is an abrupt
increase to the same final level. For sudden cardiac adverse events, intensity appears to be
more important than frequency or duration. The protective value of a medical consultation
for persons with or without chronic diseases who are interested in increasing their physical
activity level is not established.
Research Recommendations
Individual chapters in Part G: The Science Base provide a list of recommendations
regarding issues that should receive priorities for future research. The PAGAC felt that it
would be valuable to collate the major research recommendations into one section, Part H:
Research Recommendations, and to include some overarching recommendations that
pertain to more than one health outcome. For example, it became apparent during the
PAGAC’s review that various populations are underrepresented in studies on physical
activity and health. These populations represent a substantial portion of the population at
risk because of their high prevalence of sedentary behavior. They include persons of low
socioeconomic status, racial-ethnic minorities, persons with disabilities, and women during
pregnancy and the postpartum period. Also, inadequate data are available to answer a
number of questions about dose response for a variety of health outcomes, such as the
effects of activity intensity, bout duration, or frequency when total amount or volume of
activity is held constant. More data are needed to better define both the low and high ends of
the dose-response relation for various health outcomes. Additional research on the basic
biological mechanisms modified by changes in physical activity will help establish causality
for specific clinical outcomes. National surveillance systems also are needed to track trends
in total daily activity energy expenditure in various populations throughout the lifespan.
Part B:
Introduction
Setting the Stage for Physical Activity Guidelines
for Americans
The Department of Health and Human Services (HHS) is entrusted with a leadership
position in the nation’s government to promote, create, and maintain a healthy America, and
the President’s HealthierUS Initiative establishes a federal framework for wellness-related
activities and programs. In May 2006, Secretary Michael O. Leavitt announced prevention
as one of his top ten priority areas. The overarching agenda of the prevention priority is
organized around the four major principles of the HealthierUS initiative:
• Eat a nutritious diet
• Be physically active
• Get your medical screenings
• Make healthy choices
On October 27, 2006, Secretary Leavitt announced plans for the development of federal
Physical Activity Guidelines for Americans to be issued in 2008 (http://www.hhs.gov/news/
press/2006pres/20061026.html). HHS is taking the opportunity to develop the first Physical
Activity Guidelines for the nation to serve as the benchmark and single, authoritative voice
for providing science-based guidance on physical activity for health promotion. These new,
comprehensive guidelines will help promote a culture of wellness in the United States by
providing essential and practical information to Americans on physical activity and related
health benefits.
To help establish the scientific rationale for physical activity guidelines, HHS sponsored a
workshop (October 23 – 24, 2006), organized by the Institute of Medicine, in which a panel
of 30 scientists and practitioners reviewed the evidence relating habitual physical activity to
various health outcomes, with special emphasis on the prevention of major chronic diseases
(http://www.nap.edu/catalog.php?record_id=11819). This overview of existing evidence
indicated that frequent participation in physical activity was strongly linked to better health
status throughout the life span. Given the high prevalence of sedentary behavior among
Americans and the current epidemic of obesity and related diseases, the panel also
concluded that federal physical activity guidelines were warranted.
Physical Activity Guidelines Advisory Committee Report B–1
Part B. Introduction
The Physical Activity Guidelines Advisory
Committee
Following the announcement by the Secretary, nominations for potential members of a
Physical Activity Guidelines Advisory Committee (PAGAC) were sought through a
Federal Register Notice published in January 2007 (http://a257.g.akamaitech.net/7/257/
2422/01jan20071800/edocket.access.gpo.gov/2007/pdf/E7-842.pdf). Prospective members
of the Committee were expected to have knowledge of current scientific research in human
physical activity and be respected and published experts in their fields; be familiar with the
purpose, communication, and application of federal guidelines; and have demonstrated
interest in the public’s health and well-being through their research and educational
endeavors. Expertise was sought in specialty areas related to physical activity, including
health promotion and chronic disease prevention; bone, joint, and muscle health and
performance; obesity and weight management; musculoskeletal injury and other adverse
events; and applications to specific populations such as children, youth, and women during
pregnancy and the postpartum period, older adults, persons with disabilities, and diverse
races and ethnicities.
To the extent practicable, selection of committee members represented geographic
distribution and took into account the needs of the diverse groups served by HHS.
Appointments were made without discrimination on the basis of age; race and ethnicity; sex;
sexual orientation; disability; or cultural, religious, or socioeconomic status. In February
2007, Secretary Leavitt appointed 13 members to the PAGAC, including a chair and vice
chair. The Committee served without pay and worked under the regulations of the Federal
Advisory Committee Act.
Charge to the Committee
Secretary Leavitt’s charge to the Committee was to “review existing scientific literature to
identify where there is sufficient evidence to develop a comprehensive set of specific
physical activity recommendations. The Committee is to prepare a report to the Secretary
that documents scientific background and rationale for the 2008 edition of the Physical
Activity Guidelines for Americans. The report will also identify areas where further scientific
research is needed. The intent is to have physical activity recommendations for all
Americans that will be tailored as necessary for specific subgroups of the population”
(http://a257.g.akamaitech.net/7/257/2422/01jan20071800/edocket.access.gpo.gov/2007/pdf/
E7-842.pdf).
Committee Meetings
The committee held three 2-day meetings in Washington, DC, that were open to the public
and announced in the Federal Register. The meetings took place on June 26-27, 2007;
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Part B. Introduction
December 6-7, 2007; and February 28-29, 2008. Meeting summaries are available at
http://www.health.gov/paguidelines.
Oral comments from the public were presented at the second and third public meetings, and
written comments were accepted throughout the tenure of the PAGAC. Written comments
were shared with the Committee before the second and third meetings and as Committee
members were drafting their final report. These comments are available for examination at
the Office of Disease Prevention and Health Promotion, 1101 Wootton Parkway, Suite LL100, Rockville, MD 20852.
Committee Organization and Work Process
Soon after the PAGAC was convened, members decided that the work of reviewing the
science would be best achieved by establishing subcommittees, each of which would review
and interpret the literature for specific health outcomes and summarize their findings as a
chapter in the report. The subcommittees, composed of Committee members and
consultants, communicated by electronic mail and conference calls and held face-to-face
meetings before the public Committee meetings. Each subcommittee was responsible for
presenting to the full Committee the basis for its conclusions, responding to questions, and
making changes if indicated. The conclusions in this report represent the consensus of the
entire PAGAC.
Initially, the PAGAC formed 9 subcommittees, focused on the 9 health outcomes identified
by the CDC (see below): all-cause mortality, cardiorespiratory health, metabolic health,
energy balance, musculoskeletal health, functional health, cancer, mental health, and adverse
events. At their first public meeting, members added two other subcommittees: youth and
understudied populations (i.e., populations not covered in other chapters — persons with
disabilities, women during pregnancy and the postpartum period, and races and ethnicities
other than non-Hispanic white).
Each Committee member volunteered to chair one subcommittee and be a member of one or
more other subcommittees. To assist in the review process, subcommittee chairs were
authorized to select consultants who had scientific expertise in a specific area of the
subcommittee’s charge (consultants are listed at the beginning of the report).
A Systematic Review of the Evidence on Physical
Activity and Health
Immediately after Secretary Leavitt announced plans for the development of federal physical
activity guidelines, staff of the Division of Nutrition, Physical Activity, and Obesity
(DNPAO) at the Centers for Disease Control and Prevention’s (CDC’s) National Center for
Chronic Disease Prevention and Health Promotion were assigned to develop a process to
support the systematic review of the scientific literature relating physical activity to health.
The staff developed a conceptual framework for the literature search and a process to
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Part B. Introduction
systematically abstract published articles and make these abstracts readily accessible to
PAGAC members and consultants. The details of this search strategy and process are
provided in Part F: Scientific Literature Search Methodology. The product resulting from
this search and abstracting process is the Physical Activity Guidelines for Americans
Scientific Database. CDC staff initially decided to abstract relevant articles published
between January 1, 1995 and December 30, 2006. In June 2007, the PAGAC and CDC
agreed to expand the abstracting process to include articles published between January 1 and
August 10, 2007.
The Committee’s Review of the Scientific Literature
PAGAC members were instructed on and encouraged to use the Physical Activity Guidelines
for Americans Scientific Database to identify articles that would be included in each
subcommittee’s systematic review of the literature. Also, as each subcommittee developed a
plan to review and interpret the scientific data, it made arrangements with the CDC staff and
PAGAC leadership for additional abstracting of articles that were central to their review.
Because of limited time and resources available, additional abstracting was prioritized based
on the importance and relevance of the outcome being addressed. Because not all the
relevant literature could be abstracted by the CDC, subcommittees also were encouraged to
consider using recent meta-analyses or systematic reviews for various biomarkers or risk
factors that appear to be in the causal pathway between activity and a specific clinical
outcome (e.g., hypertension or atherogenic lipoproteins for coronary heart disease).
Subcommittees were instructed to carefully document in their chapters the literature search
and review methods they used.
Following their literature review, each subcommittee drafted a chapter that summarized and
synthesized the results of the review. These chapters were subsequently reviewed by at least
3 PAGAC members who were not members of the drafting subcommittee as well as selected
consultants. All PAGAC members were encouraged to review all chapters.
Summarizing and Integrating the Science
In addition to summarizing the evidence relating physical activity to individual health
outcomes, one of the PAGAC’s major goals was to integrate the scientific information on
the relation of physical activity and health and to summarize it in a manner that could be
used effectively by HHS personnel to develop the Physical Activity Guidelines and related
statements.
For the final PAGAC meeting, each subcommittee chair was requested to prepare a brief
summary of key findings from their chapter for discussion by PAGAC. Each
subcommittee’s summary report included information on the type and magnitude of
evidence, the strength of the evidence, characteristics of the physical activity most likely to
produce the outcome, any evidence of a dose-response association, and any evidence that
being sedentary puts a person at increased risk. Selected PAGAC members then were asked
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Part B. Introduction
Physical Activity Guidelines Advisory Committee Report B–5
to integrate the main conclusions from these subcommittee reports under the headings of
youth, adults, older adults, understudied populations, and adverse events. These summary
conclusions were presented and discussed at the PAGAC meeting on February 29, 2008.
The resulting summary of evidence and consensus statements about the relation of physical
activity to health are provided in Part E: Integration and Summary of the Science.
Contents and Organization of the Physical Activity
Guidelines Advisory Committee Report
The report includes 3 major components. The first component provides essential background
and synthesis information:
• Part A: Report Summary provides an executive summary of the entire report.
• Part B: Introduction provides a brief background on the formation of the Physical
Activity Guidelines Advisory Committee and the development of their report.
• Part C: Key Terms defines many of the major terms used throughout the report,
including those relating to physical activity, exercise, fitness, health, and
measurement.
• Part D: Background provides context to the current guidelines development effort
by briefly describing recent physical activity trends among Americans, by discussing
some underlying concepts about physical activity dose response, by briefly
describing recent physical activity trends among Americans, and by describing the
development of previous physical activity recommendations in the United States.
• Part E: Integration and Summary of the Science synthesizes the Committee’s
findings about the relation of physical activity to a broad array of health outcomes.
• Part F: Scientific Literature Search Methodology explains the development and use
of the Physical Activity Guidelines for Americans Scientific Database.
The second component, Part G: The Science Base, includes 11 sections that review and
summarize the scientific literature relating physical activity to individual health-related
outcomes and populations: all-cause mortality, cardiorespiratory health, metabolic health,
energy balance, musculoskeletal health, functional health, cancer, mental health, adverse
events, youth, and understudied populations.
The third component, Part H: Research Recommendations provides a summary of the
PAGAC’s collective recommendations about key areas of research that should be conducted
to further enhance the science base on physical activity and health.
Part C:
Key Terms
This section provides definitions for many of the major terms used in this report and in the
scientific literature reviewed during the preparation of the report. We have attempted to use
definitions that have been generally accepted in the scientific literature and in major reports
and recommendations for physical activity and public health. As scientists, educators, and
practitioners continue to strive to better understand new concepts and explore the numerous
characteristics of physical activity and their relations to various aspects of health and
physical fitness, new terminology is introduced and existing definitions are modified. As
new measurement tools are developed and new health outcomes are identified, accepted
terminology will continue to evolve as part of the science of physical activity and health.
Included in this section are a number of the terms that pertain to physical activity, physical
fitness, and study design. Definitions for disease or condition-specific terms are defined
within individual chapters in Part G: The Science Base. Additional discussion of the
terminology used in the presentation of research results or the development of physical
activity and public health guidelines can be found in the following publications: Public
Health Aspects of Physical Activity and Exercise (1), Toward Active Living (2), Physical
Activity and Health: A Report of the Surgeon General (3), Dose-Response Issues
Concerning Physical Activity and Health: An Evidence-Based Symposium (4), American
College of Sports Medicine’s Guidelines for Exercise Testing and Prescription (5), and
Advancing Physical Activity and Guidelines in Canada (6).
Physical Activity and Exercise
Two terms are widely used to describe human movement: physical activity and exercise.
Although they are often used interchangeably, their definitions differ.
Physical activity is any bodily movement produced by the contraction of skeletal muscle
that increases energy expenditure above a basal level. Among the ways physical activity can
be categorized is according to mode, intensity, and purpose (3). Mode and intensity are
defined below. With regard to classification by “purpose,” physical activity frequently is
categorized by the context in which it is performed. Commonly used categories include
occupational, leisure-time or recreational, household, self-care, and transportation or
commuting activities. In some studies, sports participation or “exercise training” is assessed
and analyzed separately from other leisure-time activities.
Exercise is a subcategory of physical activity that is “planned, structured, and repetitive and
purposive in the sense that the improvement or maintenance of one or more components of
physical fitness is the objective” (7). Exercise and exercise training frequently are used
Physical Activity Guidelines Advisory Committee Report C–1
Part C. Key Terms
interchangeably and generally refer to physical activity performed during leisure time with
the primary purpose of improving or maintaining physical fitness, physical performance, or
health.
Other terms that describe additional types of physical activity or exercise are defined here:
Activities of daily living. Activities required for everyday living, including eating, bathing,
toileting, dressing, getting into or out of a bed or chair, and basic mobility.
Aerobic exercise (training). Exercise that primarily uses the aerobic energy-producing
systems, can improve the capacity and efficiency of these systems, and is effective for
improving cardiorespiratory endurance.
Anaerobic exercise (training). Exercise that uses the anaerobic energy-producing systems
and can improve the capacity of these systems and increase the tolerance of acid-base
imbalance during high-intensity exercise.
Balance training. Static and dynamic exercises that are designed to improve individuals’
ability to withstand challenges from postural sway or destabilizing stimulus caused by selfmotion, the environment, or other objects.
Endurance exercise (endurance training). Exercises that are repetitive and produce
dynamic contractions of large muscle groups for an extended period of time (e.g., walking,
running, cycling, swimming).
Flexibility exercise. Exercises that enhance the ability of a joint to move through its full
range of motion.
Instrumental activities of daily living. Activities related to independent living, including
preparing meals, managing money, shopping for groceries or personal items, performing
housework, and using a telephone.
Leisure-time physical activity. Physical activities performed by a person that are not
required as essential activities of daily living and are performed at the discretion of the
person. These activities include sports participation, exercise conditioning or training, and
recreational activities such as going for a walk, dancing, and gardening.
Lifestyle activities. This term is frequently used to encompass activities that one carries out
in the course of one’s daily life, that can contribute to sizeable energy expenditure, e.g.,
taking the stairs instead of using the elevator, walking to do errands instead of driving,
getting off one bus stop earlier, or parking further away than usual to walk to a destination.
Resistance training (strength training, muscle-strengthening activities, or muscular
strength and endurance exercises). Exercise training primarily designed to increase
skeletal muscle strength, power, endurance, and mass.
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Part C. Key Terms
Terms related to patterns of physical activity or exercise are defined here:
Accumulation. The concept of meeting a specific physical activity dose or goal by
performing activity in short bouts, then adding together the time spent during each of these
bouts. For example, a 30-minute per day goal could be met by performing 3 bouts of 10
minutes each throughout the day.
Dose. In the field of physical activity, dose refers to the amount of physical activity
performed by the subject or participants. The total dose or amount is determined by the three
components of activity: frequency, duration, and intensity. Frequency is commonly recorded
as sessions, episodes, or bouts per day or per week. Duration is the length of time for each
bout of any specific activity. Intensity is the rate of energy expenditure necessary to perform
the activity to accomplish the desired function (aerobic activity) or the magnitude of the
force exerted during resistance exercise.
Dose response. The relation between the dose of physical activity and the health or fitness
outcome of interest is considered the dose response. The dose can be measured in terms of a
single component of activity (e.g., frequency, duration, intensity) or as the total amount.
This concept is similar to the prescription of a medication where the expected response will
vary as the dose of the medication is changed. The dose-response relation can be linear,
exponential, or hyperbolic, and the dose-response relation is likely to vary depending on the
primary measure of interest. For example, improvements in cardiorespiratory fitness, bone
health, or adiposity are common dose-response measures of interest. A dose of physical
activity may exist below which no effect has been detected as well as a dose above which no
effect has been detected. These seemingly lowest and highest doses of activity may be called
“thresholds,” but the term should be used cautiously as these apparent limits may be more
related to limitations of measurement than to true biological limits.
Duration. The length of time in which an activity or exercise is performed. Duration is
generally expressed in minutes.
Frequency. The number of times an exercise or activity is performed. Frequency is
generally expressed in sessions, episodes, or bouts per week.
Intensity. Intensity refers to how much work is being performed or the magnitude of the
effort required to perform an activity or exercise. Intensity can be expressed either in
absolute or relative terms.
• Absolute. The absolute intensity of an activity is determined by the rate of work
being performed and does not take into account the physiologic capacity of the
individual. For aerobic activity, absolute intensity typically is expressed as the rate of
energy expenditure (e.g., milliliters per kilograms per minute of oxygen being
consumed, kilocalories per minute, METs) or, for some activities, simply as the
speed of the activity (e.g., walking at 3 miles per hour, jogging at 6 miles per hour),
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Part C. Key Terms
or physiologic response to the intensity (e.g., heart rate). For resistance activity or
exercise intensity frequently is expressed as the amount of weight lifted or moved.
• Relative. Relative intensity takes into account or adjusts for a person’s exercise
capacity. For aerobic exercise, relative intensity is expressed as a percent of a
person’s aerobic capacity (VO2max) or VO2 reserve, or as a percent of a person’s
measured or estimated maximum heart rate (heart rate reserve). It also can be
expressed as an index of how hard the person feels he or she is exercising. A
person’s subjective assessment of how hard he or she is working relative to his/her
own capacity is called rating of perceived exertion. The Borg Scale is a commonly
used numerical scale for rating perceived exertion (8). Rating of perceived exertion
is used for both aerobic and muscle-strengthening types of activities.
MET. MET refers to metabolic equivalent and 1 MET is the rate of energy expenditure
while sitting at rest. It is taken by convention to be an oxygen uptake of 3.5 milliliters per
kilogram of body weight per minute. Physical activities frequently are classified by their
intensity, using the MET as a reference (see Table D.3 in Part D: Background).
Mode. The type of activity or exercise that is being performed. Biking, walking, rowing, and
weight lifting are all examples of different modes of activity.
Progression. The process of increasing the intensity, duration, frequency, or amount of
activity or exercise as the body adapts to a given activity pattern.
Physical Fitness
During the 20th century, physical fitness has been defined in a variety of ways, but a
generally accepted definition is “the ability to carry out daily tasks with vigor and alertness,
without undue fatigue and with ample energy to enjoy leisure-time pursuits and meet
unforeseen emergencies” (3, p.20). It has been defined by the World Health Organization as
“the ability to perform muscular work satisfactorily” (9, p.6). Physical fitness includes a
number of components consisting of cardiorespiratory endurance (aerobic power), skeletal
muscle endurance, skeletal muscle strength, skeletal muscle power, flexibility, balance,
speed of movement, reaction time, and body composition. Because these attributes differ in
their importance to athletic performance versus health, a distinction has been made between
performance-related fitness and health-related fitness (7). Performance-related fitness
includes those attributes that significantly contribute to athletic performance and places
emphasis on aerobic endurance or power, muscle strength and power, speed of movement,
and reaction time. Health-related fitness includes cardiorespiratory fitness, muscular strength
and endurance, body composition, flexibility, and balance. The relative importance of any
one attribute depends on the specific performance or health goal.
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The following terms relate to specific aspects of physical fitness.
Adaptation. The body’s response to exercise or activity. Some of the body’s structures and
functions favorably adjust to the increase in demands placed on them whenever physical
activity of a greater amount or higher intensity is performed than what is usual for the
individual. It is these adaptations that are the basis for much of the improved health and
fitness associated with increases in physical activity.
Agility. A performance-related component of physical fitness that is the ability to change
position of the entire body in space with speed and accuracy.
Balance. A performance-related component of physical fitness that involves the
maintenance of the body’s equilibrium while stationary or moving.
Body composition. A health-related component of physical fitness that applies to body
weight and the relative amounts of muscle, fat, bone, and other vital tissues of the body.
Most often, the components are limited to fat and lean body mass (or fat-free mass).
Cardiorespiratory fitness (endurance). A health-related component of physical fitness that
is the ability of the circulatory and respiratory systems to supply oxygen during sustained
physical activity. Usually expressed as measured or estimated maximal oxygen uptake
(VO2max).
Coordination. A performance-related component of physical fitness that is the ability to use
the senses, such as sight and hearing together with body parts in carrying out motor tasks
smoothly and accurately.
Flexibility. A health and performance-related component of physical fitness that is the range
of motion possible at a joint. Flexibility is specific to each joint and depends on a number of
specific variables, including but not limited to the tightness of specific ligaments and
tendons.
Maximal oxygen uptake (VO2max). The body’s capacity to transport and use oxygen during
a maximal exertion involving dynamic contraction of large muscle groups, such as during
running or cycling. It is also known as maximal aerobic power and cardiorespiratory
endurance capacity. Peak oxygen consumption (VO2peak) is the highest rate of oxygen
consumption observed during an exhaustive exercise test.
Power. A performance-related component of physical fitness that describes the rate (or
speed) at which work can be applied.
Speed. A performance-related component of physical fitness that is the ability to perform
movements rapidly or within a short period of time.
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Part C. Key Terms
Strength. A health and performance-component of physical fitness that is the ability of a
muscle or muscle group to exert force.
Health
Numerous definitions of health exist and, in this report, we have adopted the following:
“Health is a human condition with physical, social and psychological dimensions, each
characterized on a continuum with positive and negative poles. Positive health is associated
with a capacity to enjoy life and to withstand challenges; it is not merely the absence of
disease. Negative health is associated with morbidity, and in the extreme, with premature
mortality” (10, p.100).
Health-related quality of life is an individual's overall sense of well being and includes
such factors as pain, mood, energy level, family and social interactions, sexual function,
ability to work, and ability to keep up with routine daily activities.
Study Design and Measurement
Absolute risk. The percentage of subjects in a group that experiences a discrete negative
outcome, such as death or hospital admission.
Case-control study. A type of epidemiologic study design in which subjects are selected
based on the presence or absence of a specific outcome of interest, such as cancer or
diabetes. The individual’s past physical activity practices are assessed, and the association
between past physical activity and presence of the outcome is determined.
Case report. This includes single case reports of individual patients and published case
series.
Confidence interval. When relative risk (see definition below) is calculated, one can also
calculate a confidence interval, or a band of uncertainty, around the estimate of the relative
risk. Typically, 95% confidence intervals are used in epidemiologic studies. For example, if
the estimated relative risk for colon cancer associated with physical activity, compared with
inactivity, is 0.5 with a 95% confidence interval of 0.3 to 0.8, this means that we are 95%
certain that the true estimate of the relative risk lies between 0.3 and 0.8.
Cross-sectional study. Studies that compare and evaluate specific groups or populations at
a single point in time.
Observational studies. Studies in which outcomes are measured but no attempt is made to
change the outcome. The two most commonly used designs for observational studies are
case-control studies and prospective cohort studies.
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Part C. Key Terms
Odds ratio. A measure of probability used in epidemiologic studies. It measures the chances
of an event (or disease) occurring in one group of people as compared to another group with
different characteristics. For example, an odds ratio of 0.5 for high blood pressure in people
who participate in physical activity, compared with people who are inactive, indicates that
active persons are 0.5 times (50%) less likely to have high blood pressure, compared with
those who are inactive (see also Confidence interval).
Prospective cohort study. A type of epidemiologic study in which the physical activity
practices of the enrolled subjects are determined and the subjects are followed (or observed)
for the development of selected outcomes. It differs from clinical trials in that the exposure,
in this case physical activity, is not assigned by the researchers.
Randomized controlled trial (also known as a randomized clinical trial). A type of study
design in which participants are grouped on the basis of an investigator-assigned exposure of
interest, such as physical activity. For example, among a group of eligible participants,
investigators may randomly assign them to exercise at three levels: no activity, moderate
activity, and vigorous activity. These participants are then followed over time to assess the
outcome of interest, such as change in abdominal fat. Randomized controlled trials are often
considered the “gold standard” of human intervention study designs. However, because of
the cost and issues regarding compliance with an assigned activity level, it may not always
be feasible, or even desirable, to conduct this type of trial.
Relative risk. A measure of association used in epidemiologic studies. It measures the
magnitude of association between the exposure (such as physical activity) and the disease
(such as colon cancer). A relative risk of 0.5 for colon cancer associated with physical
activity, compared with inactivity, indicates that active persons have 0.5 times (or 50%) the
risk of developing colon cancer compared to inactive persons.
Retrospective study. A study in which the outcomes have occurred before the study has
begun.
Publication Types
Cochrane Collaboration. An internationally organized effort to bring existing clinical
studies into systematic reviews to facilitate the process of bringing clinical evidence to bear
on decisionmaking in patient care.
Meta-analysis. A review of a focused question that follows rigorous methodological criteria
and uses statistical techniques to combine data from studies on that question.
Systematic review. A review of a clearly defined question that uses systematic and explicit
methods to identify, select, and critically evaluate relevant research, and to collect and
analyze data from the studies to include in the review.
Physical Activity Guidelines Advisory Committee Report C–7
Part C. Key Terms
Reference List
1. Powell KE, Paffenbarger RS, Jr. Workshop on Epidemiologic and Public Health
Aspects of Physical Activity and Exercise: a summary. Public Health Rep. 1985
Mar;100(2):118-26.
2. Quinney HA, Gauvin L, Wall AE. Toward active living: proceedings of the
International Conference on Physical Activity, Fitness, and Health. Champaign, IL:
Human Kinetics; 1994.
3. United States Public Health Service, Office of the Surgeon General, National Center for
Chronic Disease Prevention and Health Promotion, President's Council on Physical
Fitness and Sports. Physical activity and health: a report of the Surgeon General.
Atlanta, Ga.: U.S. Dept. of Health and Human Services, Centers for Disease Control
and Prevention, National Center for Chronic Disease Prevention and Health Promotion;
President's Council on Physical Fitness and Sports; 1996.
4. Kesaniemi YK, Danforth E Jr, Jensen MD, Kopelman PG, Lefebvre P, Reeder BA.
Dose-response issues concerning physical activity and health: an evidence-based
symposium. Med.Sci.Sports Exerc. 2001 Jun;33(6 Suppl):S351-S358.
5. Whaley MH, Brubaker PH, Otto RM, Armstrong LE. ACSM's guidelines for exercise
testing and prescription. Philadelphia, Pa.: Lippincott Williams & Wilkins; 2006.
6. Shephard RJ, (ed.). Advancing physical activity measurement and guidelines in Canada:
a scientific review and evidence-based foundation for the future of Canadian physical
activity guidelines. Can.J.Public Health 2007;98(Suppl. 2e):s1-s224.
7. Caspersen CJ, Powell KE, Christenson GM. Physical activity, exercise, and physical
fitness: definitions and distinctions for health-related research. Public Health Rep. 1985
Mar;100(2):126-31.
8. Borg G. Borg's perceived exertion and pain scales. Champaign, IL: Human Kinetics;
1998.
9. Exercise tests in relation to cardiovascular function. Report of a WHO meeting. World
Health Organ Tech.Rep.Ser. 1968;388:1-30.
10. Preamble to the Constitution of the World Health Organization as adopted by the
International Health Conference, New York, 19-22 June, 1946; signed on 22 July 1946
by the representatives of 61 states (Official Records of the World Health Organization,
no. 2, p. 100) and entered into force on 7 April 1948. 1946.
Physical Activity Guidelines Advisory Committee Report C–8
Part D. Background
Part D:
Background
Introduction
Over the past 35 years, various health associations and agencies in the United States have
published guidelines or recommendations for health professionals and the public regarding
the health benefits and risks of being physically active. The rationale for these publications
was that on the one hand, many people were insufficiently active and needed guidance on
why and how to become more physically active, but on the other hand, an increase in
physical activity by inactive adults posed significant health risks so medical guidance was
needed. To determine how well various segments of the population are meeting these
guidelines, national public health surveillance systems have been implemented by agencies
within the US Department of Health and Human Services (HHS). The data collected by
these surveillance systems over the past decade have indicated that many youth, adults, and
older adults fail to meet these recommendations and that the rate of compliance varies
substantially by sex, age, educational achievement, socioeconomic status, and race/ethnicity.
These results are a major reason for an increased emphasis on developing federal physical
activity and public health guidelines and policy statements. In addition, a majority of the
questions now being asked about physical activity and health relate more to the dose (type,
amount, and intensity) of activity that conveys health benefits in specific populations than to
whether or not there are benefits from being physically active. Thus, it is important for the
review of the science and the development of physical activity guidelines to carefully
consider issues of dose response. This Background addresses all of these issues by
discussing several key issues related to dose response, presenting an overview of the recent
trends in physical activity by Americans, and outlining the history of physical activity and
health recommendations and guidelines in the United States.
Some Issues Regarding Dose Response
Developing physical activity recommendations for public health would be quite easy if
simply stated answers could be given to such questions as, “How much activity do I need to
be healthy?” or “How much more benefit do I get if I walk 30 minutes 6 times per week
verses just 3 times per week?” Unfortunately that does not appear to be the case. To provide
an appropriate answer to such questions, a number of issues need to be considered, including
a person’s current physical activity status, fitness level, health status, age, sex, and major
health and fitness goals. Genetic differences among individuals also influence their
responsiveness to a specific dose of activity. All of these issues affect any improvements in
health and fitness that may come from increases in various combinations of type, intensity,
duration, and frequency (the main components of dose).
Physical Activity Guidelines Advisory Committee Report D–1
Part D. Background
The Process of Adaptation
Some of the body’s structures and functions favorably adapt to the increase in demands
placed on them whenever physical activity of a greater amount or higher intensity is
performed than what is usual for the individual. It is these adaptations that are the basis for
much of the improved health and fitness associated with increases in physical activity. This
increase in activity is called overload and if applied correctly, will improve the capacity
and/or efficiency of various tissues and systems. For example, cardiac stroke volume and
skeletal muscle capillary density are enhanced in response to an increase in aerobic or
endurance activity. Many different combinations of the main components of dose can
achieve this overload. However, too big an overload applied too quickly can cause fatigue
and contribute to injury. Therefore, the overload needs to be applied progressively in
relatively small increments to allow for the body to adapt before receiving an even greater
overload. This concept is called progression. The nature of the adaptation, also called
specificity, that occurs in response to a progressive overload is influenced by the type of
activity being performed. If the overload is produced by aerobic activities like walking,
jogging, cycling or swimming, adaptations occur more to the oxygen transport system and
various metabolic processes than if the activity is a resistance activity, such as weight lifting,
which produces greater changes in muscle strength and mass. Understanding these three
principles of the biological responses to activity – overload, progression, and specificity –
helps in addressing issues about dose response to activity.
The Baseline Level of Physical Activity
The baseline level of habitual physical activity as well as the exercise capacity (physical
fitness) of a person needs to be accounted for when considering an increase in physical
activity. In other words, it is important to create an overload but not an excessive amount of
overload. Therefore, for a person who has been sedentary for some time for whatever
reason, the initial dose of activity should be at a relatively low intensity, of limited duration,
with the sessions (also called bouts) spread throughout the week. An example of this
approach would be a walking program with sessions of 5 minutes of slow walking, 5 to 6
days per week, with the bouts performed at various times throughout the day (e.g., 3 times
per day). As the person adapts to this amount of activity, the bout duration could be slowly
increased to 10 minutes, and as exercise capacity begins to increase, the walking speed
could be increased. Such an approach is based primarily on expert opinion and clinical
experience, as the benefits and risks of various approaches to initiating and progressing an
activity program for very sedentary or unfit persons have not been systematically evaluated.
Another issue regarding baseline levels of physical activity is the apparent gradual decline in
the recent decade in “routine physical activity” for an increasing proportion of the US
population. Unfortunately, in the United States and other developed or developing countries,
accurate data are not available on time trends for the total amount of physical activity
performed throughout the day (energy expenditure for activities of daily living). Recent
reports from objective measures of physical activity using accelerometers for 7 days provide
Physical Activity Guidelines Advisory Committee Report D–2
Part D. Background
some cross-sectional data on the US population. The results show that a far higher
proportion of the population is inactive than has been indicated from self-reported estimates
of physical activity (1;2). Very similar data have been reported for adults in Sweden using
similar technology (3). We still need to better understand how the results of physical activity
assessment by new objective measurement methods that can be applied to large populations
compare to data collected by commonly used questionnaires. If the time spent being
physically inactive is continuing to increase among the US population, it may be that the
starting dose of activity will need to be adjusted downward to accommodate more people
with lower exercise capacities. At the same time, the amount of activity that will have to be
added to this lower baseline to return people to being physically active by current day
standards will have to be increased.
Physical Activity Intensity
Intensity is a key factor when considering the dose of physical activity required to achieve
specific health and fitness outcomes. Not only does an increase in activity intensity play a
major role in producing many favorable adaptations, but it also has a key role in the risk of
injury during activity. In most of the studies reviewed for this report, the intensity of
physical activity was expressed either in absolute or relative values. Absolute intensity refers
to the energy or work required to perform the activity and does not take into account the
physiologic capacity of the individual. For aerobic activity, absolute intensity may be
expressed as the rate of energy expenditure (e.g., kilocalories per minutes, multiples of
resting energy expenditure [METs]) or, for some activities, simply as the speed of the
activity (e.g., walking at 3 miles per hour, jogging at 6 miles per hour). For resistance
exercise, absolute intensity is expressed as weight lifted or force exerted (e.g., pounds,
kilograms). Absolute intensity also can be classified into categories such as light, moderate,
hard, and very hard (Table D.1).
Table D.1. Classification of Physical Activity Intensity
Endurance Type Activity — Relative Intensity
Intensity
Percent
VO2R*
Percent
HRR
Percent
HRmax¥ RPE†
Very Light <20 <50 <10
Light 20-39 50-63 10-11
Moderate 40-59 64-76 12-13
Hard 60-84 77-93 14-16
Very Hard ≥85 ≥94 17-19
Maximal 100 100 20
Physical Activity Guidelines Advisory Committee Report D–3
Part D. Background
Table D.1. Classification of Physical Activity Intensity (continued)
Endurance Type Activity — Intensity (METs and %VO2max) in Healthy Adults Differing in
VO2max
Intensity
VO2max =
12 METs
METs
VO2max =
12 METs
Percent
VO2max**
VO2max =
10 METs
METs
VO2max =
10 METs
Percent
VO2max
VO2max =
8 METs
METs
VO2max =
8 METs
Percent
VO2max
VO2max =
5 METs
METs
VO2max =
5 METs
VO2max
Very Light <3.2 <27 <2.8 <28 <2.4 <30 <1.8 <36
Light 3.2-5.3 27-44 2.8-4.5 28-45 2.4-3.7 30-47 1.8-2.5 36-51
Moderate 5.4-7.5 45-62 4.6-6.3 46-63 3.8-5.1 48-64 2.6-3.3 52-67
Hard 7.6-10.2 63-85 6.4-8.6 64-86 5.2-6.9 65-86 3.4-4.3 68-87
Very Hard ≥10.3 ≥86 ≥8.7 ≥87 ≥7.0 ≥87 ≥4.4 ≥88
Maximal 12 100 10 100 8 100 5 100
Resistance-Type Exercise
Intensity
Relative
Intensity
Percent
1RM§
Very Light <30
Light 30-49
Moderate 50-69
Hard 70-84
Very Hard ≥85
Maximal 100
*%VO2R – percent of oxygen uptake reserve; %HRR – percent of heart rate reserve
¥%HRmax = 0.7305 (%VO2max) + 29.95 (4); values based on 10-MET group
†Borg Rating of Perceived Exertion 6-20 scale (5)
**%VO2max = [(100%-%VO2R) METmax-1] + %VO2R; personal communication (6)
§RM = repetitions maximum, the greatest weight that can be moved once in good form
From: Howley, E. Med Sci Sports Ex. S364-S369, 2001. (7)
Some previous physical activity and health recommendations (8), defined absolute moderate
intensity as 3.0 to 6.0 METs and vigorous intensity as more than 6.0 METs. After carefully
reviewing these classifications, the PAGAC recommends that moderate intensity be defined
at 3.0 to 5.9 METs and vigorous intensity as 6.0 or greater METs. This redefinition means
that a number of activities classified as 6.0 METs would now be considered vigorous
intensity rather than moderate intensity. A list of activities classified as 6.0 METs in the
Compendium of Physical Activity (9) is included in Table D.2.
Physical Activity Guidelines Advisory Committee Report D–4
Part D. Background
Table D.2. Physical Activities Listed as 6.0 METs in the Compendium of Physical
Activities
Compendium
Code (2000) METs
Heading
(Activity Group) Activity Description
2050 6 Conditioning
exercise
Weight lifting (free weight, nautilus or universal-type), power
lifting or body building, vigorous effort (Taylor Code 210)
2090 6 Conditioning
exercise
Slimnastics, jazzercise
2110 6 Conditioning
exercise
Teaching aerobic exercise class
4050 6 Fishing and hunting Fishing in stream, in waders (Taylor Code 670)
4080 6 Fishing and hunting Hunting, deer, elk, large game (Taylor Code 170)
4110 6 Fishing and hunting Hunting, pheasants or grouse (Taylor Code 680)
5120 6 Home activities Moving furniture, household items, carrying boxes
6050 6 Home repair Carpentry, outside house, installing rain gutters, building a
fence, (Taylor Code 640)
6180 6 Home repair Roofing
8020 6 Lawn and garden Chopping wood, splitting logs
8060 6 Lawn and garden Gardening with heavy power tools, tilling a garden, chain
saw
8110 6 Lawn and garden Mowing lawn, walk, hand mower (Taylor Code 570)
8200 6 Lawn and garden Shoveling snow, by hand (Taylor Code 610)
11030 6 Occupation Building road (including hauling debris, driving heavy
machinery)
11100 6 Occupation Coal mining, general
11192 6 Occupation Farming, taking care of animals (grooming, brushing,
shearing sheep, assisting with birthing, medical care,
branding)
11320 6 Occupation Forestry, planting by hand
11380 6 Occupation Horse grooming
11560 6 Occupation Shoveling, light (less than 10 pounds/minute)
11780 6 Occupation Using heavy power tools such as pneumatic tools
(jackhammers, drills, etc.)
12010 6 Running Jog/walk combination (jogging component of less than 10
minutes) (Taylor Code 180)
15050 6 Sports Basketball, non-game, general (Taylor Code 480)
15110 6 Sports Boxing, punching bag
Physical Activity Guidelines Advisory Committee Report D–5
Part D. Background
Table D.2. Physical Activities Listed as 6.0 METs in the Compendium of Physical
Activities (continued)
Compendium
Code (2000) METs
Heading
(Activity Group) Activity Description
15190 6 Sports Drag racing, pushing or driving a car
15200 6 Sports Fencing
15500 6 Sports Paddleball, casual, general (Taylor Code 460)
15640 6 Sports Softball, pitching
15680 6 Sports Tennis, doubles (Taylor Code 430)
15730 6 Sports Wrestling (one match = 5 minutes)
15733 6 Sports Track and field (high jump, long jump, triple jump, javelin,
pole vault)
16040 6 Transportation Pushing plane in and out of hangar
17027 6 Walking Carrying 16 to 24 lb load, upstairs
17080 6 Walking Hiking, cross country (Taylor Code 040)
17210 6 Walking Walking, 3.5 mph, uphill
18150 6 Water activities Skiing, water (Taylor Code 220)
18300 6 Water activities Swimming, lake, ocean, river (Taylor Codes 280, 295)
18310 6 Water activities Swimming, leisurely, not lap swimming, general
19010 6 Winter activities Moving ice house (set up/drill holes, etc.)
19160 6 Winter activities Skiing, downhill, moderate effort, general
NOTE: This table is adapted from The Compendium of Physical Activities (9).
In contrast, relative intensity takes into account or adjusts for a person’s exercise capacity.
For aerobic exercise, relative intensity is expressed as a percent of a person’s aerobic
capacity (VO2max) or VO2 reserve, as a percent of a person’s measured or estimated
maximum heart rate or heart rate reserve, or as an index of how hard the person feels he or
she is exercising (rating of perceived exertion) (10). A percent of maximum heart rate or
heart rate reserve can be used because a near linear relation exists between the increase in
heart rate and the increase in oxygen uptake during dynamic aerobic exercise. Table D.1
also provides the classification of physical activity intensity showing the relation between
absolute and relative intensity for aerobic activity and relative intensity for resistance
exercise.
In most experimental studies evaluating the effects of increased activity on various fitness
and health outcomes, intensity is expressed relative to each person’s capacity (e.g., 60% to
75% of VO2max). However, in nearly all of the large prospective observational studies,
Physical Activity Guidelines Advisory Committee Report D–6
Part D. Background
physical activity intensity is expressed in absolute terms (no adjustment made for each
person’s exercise capacity). These differences in methodology limit to some degree direct
comparison of dose-response data from these 2 major sources of evidence. For an activity of
a given absolute intensity, such as walking at 3.0 miles per hour (3.3 METs), the relative
intensity varies inversely to the aerobic capacity of the individual. As shown in Figure D.1,
for highly fit people with an aerobic capacity of 14 METs, walking at 3.0 miles per hour has
a relative intensity of 24 % (left y-axis) or light intensity (right y-axis), but for people of low
fitness who have only a 4-MET capacity, the relative intensity is at 83% (left y-axis) or hard
intensity (right y-axis). A similar situation is displayed for a walking speed of 4.0 miles per
hour with a MET value of 5.0. Note that it is impossible for people with a 4-MET capacity
to walk this fast for an extended period of time, as the energy requirement exceeds their
aerobic capacity. Standardization of activity intensity classification is essential for
accurately establishing the relation between intensity and health or fitness outcomes.
Figure D.1. The Relative Exercise Intensity for Walking at 3.0 mph (3.3 METs) and
4.0 mph (5.0 METs) Expressed as a Percent of VO2max for Adults With an
Exercise Capacity Ranging from 4 to 14 METs
Exercise Capacity in METs
Relative Intensity
Classification
Percent VO2 max
0
20
40
60
80
100
120
140
4 6 8 10 12 14
3 mph
4 mph
83%
55%
41%
33%
28% 24%
125%
83%
63%
50%
42%
36%
Maximal
Very Hard
Hard
Moderate
Light
Very Light
(Exceeds capacity)
Figure D.1. Data Points
Exercise
Capacity
METs
4
METs
6
METs
8
METs
10
METs
12
METs
14
3 mph 83 55 41 32 28 24
4 mph – 83 63 50 42 36
Physical Activity Guidelines Advisory Committee Report D–7
Part D. Background
Physical Activity Amount
The amount of physical activity performed by a person for a given period of time is the
product of activity duration, absolute intensity, and frequency. Thus, the amount of activity
is one expression of activity dose. For many of the prospective observational studies cited in
this review, the primary activity exposure is the amount of leisure-time or total physical
activity expressed in minutes or hours per day or week (of moderate, vigorous, or moderate
plus vigorous activity), distance walked or jogged/run per day or week. Exposure also can
be the estimated amount of energy expended expressed in kilocalories per day or week,
kilocalories per kilogram of body weight per day or week, or MET-minutes or MET-hours
per day or week.
In experimental studies, the amount of activity sometimes has been expressed in these same
units but also has been given with the intensity in relative units along with the frequency and
duration of the activity sessions with no overall amount or volume of activity provided
(e.g., 30 minutes at 70% heart rate reserve [HRR], 5 times per week for 24 weeks). To pool
or compare results across studies and develop generalized conclusions about the benefits
provided with various amounts of physical activity, it was necessary to be able to compare
one expression of the amount of activity with others. Table D.3 provides this type of
information for walking, jogging, and running over a range in activity intensity from 3.0 to
16.0 METs.
Table D.3. Walk, Jog, and Run Speeds and METs, MET-Minutes, MET-Hours, and
Distance (miles) for 2.5 Hours (150 min) and 5.0 Hours (300 min) per
Week of Physical Activity. Also Listed Are the Estimated Kilocalories
(kcal) Expended by a 75 kg (165 lb) Adult During 150 and 300 Minutes
per Week at the Different Intensities of Activity.
Speed
(mph) METs
For 2.5
hr/wk
(150
min/wk)
MET-min
For 2.5
hr/wk
(150
min/wk)
MET-
hours
For 2.5
hr/wk
(150
min/wk)
Miles
For 2.5
hr/wk
(150
min/wk)
kcal
For 5.0
hr/wk
(150
min/wk)
MET-min
For 5.0
hr/wk
(150
min/wk)
MET-
hours
For 5.0
hr/wk
(150
min/wk)
Miles
For 5.0
hr/wk
(150
min/wk)
kcal
Rest 1.0 150 2.5 0.0 190 300 5.0 0.0 380
2.5 3.0 450 7.5 6.25 565 900 15.0 12.5 1,130
3.0 3.3 495 8.25 7.5 620 990 16.5 15.0 1,240
4.0 5.0 750 12.5 10.0 940 1,500 25.0 20.0 1,880
4.3 6.0 900 15.0 10.75 1,125 1,800 30.0 21.5 2,250
5.0 8.0 1,200 20.0 12.5 1,500 2,400 40.0 25.0 3,000
6.0 10.0 1,500 25.0 15.0 1,875 3,000 50.0 30.0 3,750
7.0 11.5 1,725 28.25 17.5 2,155 3,450 56.5 35.0 4,310
8.0 13.5 2,025 33.75 20.0 2,530 4,050 67.5 40.0 5,060
10.0 16.0 2,400 40.0 25.0 3,000 4,800 80.0 50.0 6,000
2.5 - 4.3 mph = walk
5-10 mph = jog/run
† kilocalories for 75 kg adult when exercising at the given intensity for either 150 or 300 minutes.
Note: These are gross energy expenditure values during exercise; thus, they include the energy expenditure at rest and not
just the additional energy expenditure due to the activity. Kilocalories calculated using 1 MET = 1 kilocalorie per kilogram per
hour and rounded to nearest 5 kilocalories. MET values from Ainsworth and colleagues (9).
Physical Activity Guidelines Advisory Committee Report D–8
Part D. Background
Based on data in this table, for 2.5 hours per week of activity at moderate absolute intensity
(3.0 to less than 6.0 METs), a person would have a range for MET-minutes per week of
450 to less than 900, MET-hours per week of 7.5 to less than 15.0 and, if they weighed
165 pounds (75 kilograms), their kilocalories of energy expenditure would range from
565 to less than 1,125 kilocalories. If this were achieved by walking at various speeds, the
distance would range from 6.25 to less than 10.75 miles per week. At 5 hours per week of
moderate-intensity activity, the MET-minutes per week would range from 900 to less than
1,800 and MET-hours per week would range from 15.0 to less than 30.0. Kilocalories
expended by a 165-pound (75 kilogram) adult would range from 1,130 to less than
2,250 and the distance walked would be 12.5 to less than 21.5 miles.
The energy expenditure values in Table D.3 are estimated gross values. They include both
the energy expenditure required at rest (1 MET) as well as the added (net) energy
expenditure required for performing the activity. The estimated energy expenditure for a
165-pound (75 kilogram) person at rest for 150 minutes during the week is about
190 kilocalories. If that person instead walked at a 3.0 mile per hour pace for the
150 minutes, his or her estimated energy expenditure during this time would be about
620 kilocalories, or an increase above rest of 430 kilocalories. However, if the person jogged
at a 6 mile per hour pace for these 150 minutes, he or she would expend approximately
1,875 kilocalories, or an increase above rest of about 1,685 kilocalories. Thus, a 165-pound
person jogging at 6 miles per hour for 150 minutes per week would expend approximately
1,255 more kilocalories than if he or she walked at 3 miles per hour for the same amount of
time during the week. This example demonstrates the substantial increase in energy
expenditure as the intensity of the activity increases. In this example, the increase in
kilocalories while jogging is nearly 4 times greater than the increase while walking
(430 versus 1,655).
Recent Trends in Physical Activity in the United
States
Since the 1995 physical activity and public health recommendations published by the
Centers for Disease Control and Prevention and the American College of Sports Medicine
(8) and Physical Activity and Health: A Report of the Surgeon General published in 1996
(11), national health behavior surveillance systems have collected cross-sectional
information on self-reported compliance with these recommendations by representative
samples of Americans. The major national public health surveillance systems monitoring
physical activity in the US population include the Behavioral Risk Factor Surveillance
System (BRFSS; http://www.cdc.gov/brfss/), the Youth Risk Behavior Surveillance System
(YRBSS; http://www.cdc.gov/HealthyYouth/yrbs/), National Health and Nutrition
Examination Survey (NHANES; http://www.cdc.gov/nchs/nhanes.htm), and the National
Health Interview Survey (NHIS; http://www.cdc.gov/nchs/nhis.htm). For details regarding
the methodologies used by each of these surveys, readers are referred to their respective
websites. These surveys provide snapshots of participation in selected types or categories of
Physical Activity Guidelines Advisory Committee Report D–9
Part D. Background
activities by adults and youth and participation in structured programs of activity, such as
physical education and organized sports in youth. They include measures of inactivity as
well as of activity and, in many cases, include information through 2005. No surveillance
system exists that captures an overall determination of physical activity performed or the
energy expended during activity throughout the day – during work, school, home and self
care, commuting, and leisure time. However, one systematic review of physical activity
trends over the past 50 years suggest that declines have occurred in work-related activity,
self-transportation activity, and activity in the home, resulting in overall decrease in physical
activity (12).
Adults and Older Adults
The BRFSS is a state-based random-digit dialed telephone survey of the noninstitutionalized US civilian population aged 18 years and older. Beginning in 2001, BRFSS
included biannual questions about leisure-time physical activity asking whether respondents
participated in either moderate- or vigorous-intensity activity in bouts of at least 10-minute
duration. If they did, respondents were asked to report the frequency and duration of these
activities (13). Participants who reported at least 30 minutes of moderate-intensity activity
5 or more days per week or 20 minutes of vigorous-intensity activity 3 or more days per
week, or both were considered to be engaged in regular physical activity and to meet current
recommendations. In 2005, the prevalence of women reporting that they regularly engaged
in physical activity was 46.7%, which was a relative increase of 8.6% from 2001 (43.0%),
while men increased 3.5%, from 48.0% to 49.7%. For women, a significant increase
between 2001and 2005 was reported in all racial/ethnic groups and all age and education
level categories except for women aged 18 to 24 years (Figure D.2). Among men, significant
increases were observed for the age range 45 to 64 years, non-Hispanic whites, nonHispanic blacks, high school graduates and college graduates.
As can be seen in Figure D.2, the percentage of men who reported being physically active is
greater than for women and steadily declines with age in both sexes. The prevalence at age
18 to 24 years is 60.5% for men and 50.8% for women, but significantly decreases by age
65 years and older to 43.1% in men and 32.2% in women. For both men and women, higher
levels of education were associated with a higher prevalence of reporting being physically
active, ranging from 35.5% and 34.2% for men and women who had not graduated from
high school up to 52.6% and 49.1% for men and women who were college graduates.
Non-Hispanic white men and women tend to have a higher reported prevalence of being
active than other racial/ethnic groups with the largest differences in 2005 being between
non-Hispanic white and black women and between non-Hispanic white men and Hispanic
men.
The data presented in Figure D.2 are quite consistent with self-report data from other
national surveys conducted over the past decade.
Physical Activity Guidelines Advisory Committee Report D–10
Part D. Background
Figure D.2. Estimated Age Adjusted Percentage of Persons ≥18 Years Reported
Meeting the Healthy People 2010 Objective for Regular Physical
Activity in 2001 and 2005: Data from BRFSS
0
10
20
30
40
50
60
W--NH B-NH H Other W-NH B-NH H Other
0
10
20
30
40
50
60
70
18-24 25-34 35-44 45-64 =65 18-24 25-34 35-44 45-64 =65
0
10
20
30
40
50
60
< HS HS
grad
Some
C
C grad grad
Some
C
C grad
Race - Ethnicity Education
Age (years)
Men Women Men Women
Men Women
% %
%
2001 2005
W = White, H = Hispanic, B = Black
NH = non-Hispanic, HS = high school, C = college
Grad = graduate
Figure D.2. Data Points Age
Year
Men
18-24
Men
25-34
Men
35-44
Men
45-64
Men
*65
Women
18-24
Women
25-34
Women
35-44
Women
45-64
Women
*65
2001 60.5 51.4 47.8 43.3 43.1 50.6 47.7 46.2 40.6 32.2
2005 62 51.5 49.6 46.5 44.5 52.7 50.5 49.7 45.5 36.3
Figure D.2. Data Points Race — Ethnicity
Year
Men
W--NH
Men
B-NH
Men
H
Men
Other
Women
W-NH
Women
B-NH
Women
H
Women
Other
2001 50.6 40.3 42 43.1 46 31.4 36.3 41.2
2005 52.3 45.3 41.9 45.7 49.6 36.1 40.5 46.6
Figure D.2. Data Points Education
Year
Men
< HS
Men
HS grad
Men
Some C
Men
C grad
Men

Men
HS grad
Men
Some C
Men
C grad
2001 35.8 46 50.3 52.6 34.2 40.3 44.3 49.1
2005 37.2 47.9 50.3 54.6 37.1 43.2 47.9 53.3
Physical Activity Guidelines Advisory Committee Report D–11
Part D. Background
Figure D.3 displays data from the Healthy People 2010 Database (DATA2010) for men and
women combined for selected measures of physical activity reported annually from 1997 to
2006 (14). Over this period, 30% to 35% of adults reported participation in moderate- or
vigorous-intensity activity sufficient to meet existing recommendations, and those reporting
no leisure time activity remained in the 35% to 40% range. Neither of these measures
showed a consistent trend over time. From 1997 through 2000, approximately 16% of the
adult population reported performing muscle strength and endurance exercises, with an
increase to about 20% being reported from 2001 to 2006.
Figure D.3. Reported Physical Activity by Adults in the USA: 1997-2006 The
Healthy People 2010 Database
0
5
10
15
20
25
30
35
40
45
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
No leisure-time physical activity
Regular moderate or vigorous physical activity
Muscle strength and endurance activities
%
Figure D.3. Data Points
Activity 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
No leisure-time physical
activity
40 40 39 39 38 38 37 39 40 39
Regular moderate or
vigorous physical activity
32 30 30 32 32 32 33 30 30 31
Strength and endurance
activities
18 18 18 18 20 20 20 20 20 19
Depending on how the questions are asked and the activity classification criteria used,
responses to the various national physical activity surveillance systems indicate that 45% to
50% of adults in the US report meeting current public health recommendations for
moderate-to-vigorous physical activity (defined as moderate-intensity activities [i.e., brisk
Physical Activity Guidelines Advisory Committee Report D–12
Part D. Background
walking, bicycling, vacuuming, gardening, or anything else that causes small increases in
breathing or heart rate] for at least 30 minutes per day at least 5 days per week, or vigorousintensity activities [i.e., running, aerobics, heavy yard work, or anything else that causes
large increases in breathing or heart rate] for at least 20 minutes per day at least 3 days per
week, or both). About 38% to 40% report being insufficiently active (defined as doing more
than 10 minutes total per week of moderate- or vigorous-intensity lifestyle activities
[i.e., household, transportation, or leisure-time activity] but less than the recommended level
of activity). Around 25% report performing no moderate-to-vigorous physical activity
during leisure time (defined as no physical activities or exercises such as running,
calisthenics, golf, gardening, or walking in the previous month), and approximately 15% are
considered inactive (defined as less than 10 minutes total per week of moderate- or
vigorous-intensity lifestyle activities [i.e., household, transportation, or leisure-time
activity]. Figure D.4 provides data from the BRFSS for 2001-2005 for all adults combined
(13).
Figure D.4. Reported Physical Activity by Adults in the USA: 2001-2005
Data from BRFSS
0
10
20
30
40
50
60
2001 2003 2005
Recommended
Insufficient
Inactive
No LTPA
"Recommended," "Insufficient," and "Inactive" data comprise one measure, and responses should sum to ~100%. "No
Leisure-Time Physical Activity" is a separate question, and should not be included with calculations for the recommended,
insufficient, or inactive.
Figure D.4. Data Points
Physical Activity 2001 2003 2005
Recommended 45.3 46.9 48.8
Insufficient 38.6 38.5 37.7
No leisure-time physical activity 26.3 24.6 25.4
Inactive 16.0 15.6 14.2
Physical Activity Guidelines Advisory Committee Report D–13
Part D. Background
Youth
Based on data from the YRBSS for 2005, 35.8% of high school students reported meeting
current physical activity recommendations (defined as performing any kind of physical
activity that increased their heart rate and made them breathe hard some of the time
(i.e., moderate or vigorous intensity) for at least 60 minutes per day on 5 or more days of the
7 days preceding the survey) (5). The reported prevalence of meeting this level of physical
activity was higher in boys (43.8%) than girls (27.8%) and higher in white (46.9%), black
(38.2%), and Hispanic (39.0%) boys than for white (30.2%), black (21.3%), and Hispanic
(26.5%) girls. Prevalence estimates of meeting current recommendations of at least 60
minutes per day 5 or more days per week of moderate- or higher-intensity activity ranged
from 26.9 to 45.9% across state surveys (median 33.9) for students in grades 9-12.
The recommended level of physical activity used as a benchmark by the YRBSS before the
2005 survey was either 20 minutes of vigorous-intensity activity (activities that make a
person sweat and breathe hard) at least 3 days per week or at least 30 minutes of moderateintensity activity (activity that does not cause a person to sweat or breathe hard) on at least
5 days per week. The percentage of students meeting these recommendations in 2005 was
substantially higher than for the updated 60 minutes per day recommendations: boys
(75.8%) were higher than girls (61.5 %) and white (77.0%), black (71.7%), and Hispanic
(76.0) boys had higher compliance rates than did white (63.3%), black (53.1%), and
Hispanic (62.6%) girls. Students reporting not participating in any moderate or vigorous
intensity activity during the past 7 days was 7.6% nationwide, with a higher prevalence
among girls (11.3%) than among boys (7.9%) and higher among black (14.4%) than white
(8.1%) and Hispanic students (10.6%).
In 2005, 54.2% of high school students reported attending a physical education (PE) class
one or more days per week on an average week they were in school with a higher percentage
of boys (60.0%) reporting yes than girls (48.3%) and higher percentages of white (58.1%),
black (61.7%), and Hispanic (65.9%) boys reporting yes than white (46.1%), black (50.5%),
and Hispanic (57.5%) girls. The prevalence of attending PE class at least one day per week
varied by state from a low of 25.2% to a high of 94.2%. However, when the frequency
criteria for attending PE class was increased from 1 day per week to 5 days in an average
week, the prevalence decreased to 37.1% for boys and 29.0% for girls, with the variation
among states ranging from 6.7% to 60.7%.
Based on data from the various physical activity questions contained in the YRBSS for
2005, high school boys tend to meet moderate-to-vigorous physical activity
recommendations more frequently than do girls, with this sex difference being true for
white, black, and Hispanic youth. Overall, it appears that white high school students report
being somewhat more active than Hispanic and black students, but their attendance in PE
classes does not appear to be any different.
Physical Activity Guidelines Advisory Committee Report D–14
Part D. Background
Figure D.5 displays the trends for various indices of physical activity for high school
students for the period 1999-2005 collected using the YRBSS (14). Included are the
percentage of students who met the previous recommendations of either moderate- or
vigorous-intensity activity, students reporting no moderate or vigorous physical activity, and
the percentage of students reporting attending PE class 5 days per week on average or at
least one day per week. The overall impression gained from the data displayed in this figure
is that over this 7-year period, neither reported activity meeting moderate-to-vigorous
physical activity recommendations or attendance in high school PE classes changed much.
The prevalence of students not reporting any moderate-to-vigorous physical activity over the
past week also has remained quite constant.
Figure D.5. Percent of High School Students in the United States with Various
Physical Activity Profiles: 1999-2005 Data from YBRFSS
0
10
20
30
40
50
60
70
80
1999 2001 2003 2005
No Reported MVPA
Attend Physical Education Class ≥1 Time per Week
Meets Previous MVPA Physical Activity Recommendations
%
Attend Physical Education 5 Times per Week on Average
Figure D.5. Data Points
Activity 1999 2001 2003 2005
Meet moderate or vigorous physical activity 69.5 68.6 66.6 68.7
Physical education class 5 times per week 56.1 51.7 55.7 54.2
Physical education class ≥1 time per week 29.1 32.2 28.4 33
No moderate or vigorous physical activity 9.4 9.5 11.5 9.6
Physical Activity Guidelines Advisory Committee Report D–15
Part D. Background
Comment on Measures of Physical Activity Trends in the United
States
As mentioned previously, no national surveillance system in the United States attempts to
document all activity performed throughout the day. Also, no national surveillance system
exists to track physical activity of young children not yet in high school or to specifically
target the rapidly increasing older population. The results of the national surveillance
systems cited above generally indicate some small changes in the activity status of youth
and adults in the past 5 to 10 years, primarily based on whether or not they meet current
physical activity recommendations. Data from the BRFSS for 2001-2005 do demonstrate a
6% or so relative increase in adults meeting moderate-to-vigorous physical activity
recommendations, and other BRFSS data for the period 1994-2004 indicate that the
percentage of the population who reported no LTPA decreased from 29.8% in 1994 to
23.7% in 2004 (13). However data collected using the NHIS indicate that the percentage of
adults who engaged in regular leisure-time physical activity did not change between 1997
and 2006.
Overall, the data provided by these national surveillance programs consistently demonstrate
that a majority of adults do not meet current physical activity and public health
recommendations. Although about two-thirds of high school students report meeting
previous moderate-to-vigorous physical activity recommendations (at least 30 minutes of
moderate intensity activity at least 5 days per week, or vigorous intensity activity at least
20 minutes at least 3 times per week), only 35.8% report meeting the current
recommendations (at least 60 minutes per day of moderate or vigorous intensity activity on
at least 5 days per week) (5). Also, any changes in the various indices of physical activity for
high school students have been small and inconsistent over the past decade.
The use of self-report instruments to monitor physical activity over time is known to have a
variety of limitations given the diversity of activities that are performed daily by people with
different jobs, home care responsibilities, commuting patterns, and leisure-time pursuits.
Attempting to obtain adequate detail so that accurate classifications of activity status can be
made based on type, intensity, and amount of activity is difficult and can lead to inaccurate
information and increased non-response. Until recently, no real option existed for collecting
physical activity surveillance data other than by self-report. However, over the past decade,
the technology of objective physical activity monitors, especially accelerometers, that can be
used in large and diverse populations has developed substantially. Initially, these monitors
were used in small-scale studies, but accelerometer data describing the physical activity
patterns in relatively large (n=1,100 to 6,800) samples (1-3) has recently been published.
These initial reports demonstrate the substantial potential for the use of such devices in
national physical activity surveillance programs but also present a challenge for analyzing
the large amounts of data they produce and interpreting results. For example, accelerometers
were used to collect NHANES data minute by minute during waking hours over 7 days in
approximately 6,800 children, adolescents, and adults (1). Based on these data, 42% of
children aged 6 to 11 years met the current 60 minutes per day recommendation but only 8%
Physical Activity Guidelines Advisory Committee Report D–16
Part D. Background
Physical Activity Guidelines Advisory Committee Report D–17
of adolescents met this goal and fewer than 5% of adults met the 30 minutes or more per day
recommendation. These estimates of physical activity participation are substantially lower
than those obtained in nationally representative surveys by self-report described above. The
reasons for the differences are not clear. One reason may be participant over-estimation of
physical activity in self-report surveys. Alternatively, accelerometers may not be accurately
capturing all reported physical activity for a variety of reasons. Most likely, some
combination of reasons explain the disparity. A much better understanding of how objective
physical activity measurements obtained with currently available and new instrumentation
relate to a variety of health outcomes is needed before such measurements can be used to
inform future physical activity recommendations and policy statements.
Development of Physical Activity Guidelines in the
United States1
By the late 1960s, a number of individuals and organizations in the United States had
recognized the increasingly sedentary nature of the population and the negative health and
fitness consequences of this decline in activity, and were promoting their own interpretation
of a good or best exercise program. Data from a growing number of observational and
experimental studies supported the value of being physically active, but no consensus
existed on what programs were most effective and safe. Also, during the early 1960s, death
rates from coronary heart disease were still on the rise and few effective treatments for
preventing sudden cardiac death were available. It was well established that the increased
work of the heart during vigorous exercise could trigger cardiac arrest or myocardial
infarction in persons with coronary atherosclerosis. However, investigators and clinicians
lacked an understanding of the etiology of the atherothrombotic disease process, how to
detect it in at-risk populations, and what types and intensities of exercise were safe. Many
people, including physicians, were very concerned about adults older than age 45 years
increasing their physical activity, especially starting a vigorous exercise program or
participating in athletic competition. It was this combination of concern about the need to
promote exercise, but at the same time, fear that promoting exercise, if not carefully
controlled, would cause many people to experience sudden cardiac death that precipitated
the development of the first physical activity guidelines and recommendations. The
evolution of the guideline process over a 35-year period has been characterized by attempts
to reduce risk while maximizing benefit by providing clinically-oriented recommendations
for patient or “at-risk” populations and by public health-oriented recommendations for the
general public.
1 This overview of the development of physical activity guidelines in the United States was adapted from a
chapter prepared by W. Haskell for Epidemiologic Methods in Physical Activity (15). Its use in this report was
approved by the publisher.
Part D. Background
Early Development of Physical Activity Recommendations and
Guidelines
By the early 1970s, data from several epidemiologic and experimental studies demonstrated
that physically active persons, including patients with coronary heart disease (CHD), had
better health outcomes than did their less active counterparts. These data were useful in
preparing early guidelines because the major concern was how to minimize risk while
achieving health benefits. The earliest such guidelines were published by the American
Heart Association (AHA) in 1972 and 1975. The first publication was Exercise Testing and
Training of Apparently Healthy Individuals: A Handbook for Physicians (16). These
guidelines were directed more at reducing the cardiovascular risk imposed by performing
moderate- to vigorous-intensity exercise, including exercise testing for the “coronary
prone,” than at providing information on how to help patients become more physically
active. The authors indicated that available data supported exercise in the rehabilitation of
patients with CHD, but data were still inadequate to support widespread promotion of
exercise for the prevention of CHD. The authors also advised that the exercise
recommendations for the healthy but sedentary person, particularly for the middle-aged
male, “not be arbitrarily formulated” and that “exercise intensity must be adjusted to
individual capacity at the beginning of the program and regulated periodically during the
succeeding stages.”
The AHA’s second publication, Exercise Testing and Training of Individuals with Heart
Disease or at High Risk for its Development: A Handbook for Physicians, also focused more
on assessment of exercise capacity and issues of risk than on details of program
implementation, and more on rehabilitation than on secondary prevention (17). The
following quote from the publication is an indication of the clinical approach taken to
exercise guidelines in the 1970s: “Exercise is a therapeutic agent designed to promote a
beneficial clinical effect and, as such, has specific indications and contraindications and
possible toxic or adverse reactions” (page 24).
During this same time period, several professional organizations and government agencies
began to issue recommendations, guidelines, and position stands on the importance of being
physically active, how much of what types of activity should be performed, and how best to
implement a safe activity plan to increase health and fitness. In 1973, Exercise and Sport
Sciences Reviews published “The Quantification of Exercise Training Programs,” a review
of research on endurance exercise training and cardiorespiratory fitness by Michael Pollock
(18). Much of the information developed during this review was used by Pollock and
colleagues as the scientific basis for the first American College of Sports Medicine (ACSM)
Position Statement on “The Recommended Quantity and Quality of Exercise for Developing
and Maintaining Fitness in Healthy Adults,” which was published in 1978 (19). This
Position Statement focused on “developing and maintaining cardiorespiratory fitness and
body composition in healthy adults,” and its key recommendations were that individuals
perform an endurance-type activity for 15 to 60 minutes, 3 to 5 days per week, at 60% to
90% of heart rate reserve or 50% to 85% of maximal oxygen uptake. Although reasonably
Physical Activity Guidelines Advisory Committee Report D–18
Part D. Background
brief (2.5 pages of text and 90 references), the recommendations in this document became
the mainstay for most exercise professionals and much of the public wanting to know, “How
much exercise is enough?” It is worthwhile noting that all the references cited in this
document were from the field of exercise physiology, with none from physical activity or
behavioral epidemiology.
The ACSM reissued this Position Stand in 1990 and changed the title to “The
Recommended Quantity and Quality of Exercise for Developing and Maintaining
Cardiorespiratory and Muscular Fitness in Healthy Adults” (20). The dose of exercise
recommended was quite similar to the 1978 recommendation, with frequency and exercise
mode remaining the same, session duration changing from “15 to 60” minutes to “20 to 60”
minutes, and intensity changing from “60% to 90% of heart rate reserve or 50% to 85% of
maximal oxygen uptake” to “60% to 90% of maximum heart rate or 50% to 85% of
maximal oxygen uptake or heart rate reserve.” A specific recommendation for enhancing
muscle strength was added: one set of 8 to 12 repetitions of 8 exercises, 2 days per week.
The statement also indicated that less intensive exercise might also provide health benefits:
“ACSM recognizes the potential health benefits of regular exercise performed more
frequently and for a longer duration, but at lower intensities than presented in this position
statement.” (p. 266).
In 1998, the ACSM published the third edition of its Position Stand, entitled, “Quantity and
Quality of Exercise for Developing and Maintaining Cardiorespiratory and Muscular
Fitness, and Flexibility in Healthy Adults” (21). The primary recommendations for exercise
to enhance cardiorespiratory and body composition remained similar to the 1978 and 1990
recommendations except for a small reduction at the low end of the intensity range: 55% to
90% of maximum heart rate instead of 60% to 90% or 40% to 85% of maximal oxygen
uptake reserve or heart rate reserve instead of 50% to 85%. This 1998 document also
included recommendations for flexibility and adopted the concept of accumulation from
public health recommendations published by the Centers for Disease Control and Prevention
(CDC) and ACSM in 1995 (8). (See the following section for more details on the 1995
CDC/ACSM recommendations.) In discussing “duration of training, the ACSM Position
Stand recommended “20 to 60 minutes of continuous or intermittent (minimum of
10-minute bouts accumulated throughout the day) of aerobic activity.”
In addition to these Position Stands, the ACSM as well as other organizations developed
publications that provided detailed guidelines for specialists such as physicians, exercise
scientists, physical educators, physical therapists, coaches, and nurses. These guidelines
were intended for use in providing exercise and fitness evaluations, developing physical
activity prescriptions or plans for individuals or groups, and providing exercise instruction
or leadership for patients and healthy persons. Included in these documents were the
7 editions of Guidelines for Exercise Testing and Exercise Prescription published by the
ACSM between 1975 and 2005 (10;22-27) and Exercise Standards: A Statement for
Healthcare Professionals from the American Heart Association (28).
Physical Activity Guidelines Advisory Committee Report D–19
Part D. Background
A Paradigm Shift to Public Health Physical Activity Guidelines
Starting in the mid-1980s, various medical and public health organizations held discussions
and published manuscripts on public health rather than clinical approaches to physical
activity for achieving improved health outcomes (29). For example, CDC’s Behavioral
Epidemiology and Evaluation Branch organized a “Workshop on the Epidemiological and
Public Health Aspects of Physical Activity and Exercise” in 1984, in which experts
reviewed the current knowledge base relating physical activity to health status and identified
actions to be taken to increase the activity status of Americans (30). Ten manuscripts were
prepared as the basis for discussion during the conference, and they were published along
with a conference overview (31). This meeting played a significant role in setting the stage
for the evolution of a public health paradigm for physical activity over the next decade.
The goal of this effort was to augment or supplement, but not necessarily replace, the
existing exercise-for–fitness paradigm promoted by the ACSM and other organizations by
focusing primarily on enhancing physical fitness or working capacity, either in healthy
persons or in the rehabilitation of various patient populations (32). During this 10-year
period, substantial new data were published, especially from physical activity epidemiology,
which related inactivity to increased risk of several chronic diseases and the potential
protective effects of moderate-intensity, as well as vigorous-intensity activity. In addition,
researchers reconsidered some of the prior epidemiologic data with respect to the most likely
kinds and patterns of physical activity that were carried out by active people, who comprised
some of the lower-risk groups. The tentative conclusion was that much of this risk-reducing
activity was of moderate intensity (usually considered 3.0 to 6.0 METs) and that it was
frequently performed in repeated short bouts. Thus, a disconnect appeared to exist between
the accepted exercise-fitness paradigm, which emphasized vigorous activity performed in
bouts of at least 20 minutes duration, and the intensity and bout duration that appeared to
provide some protection against selected chronic diseases and all-cause mortality.
For example, the results of some studies indicated that regular walking or other moderateintensity activity, or moderate levels of cardiorespiratory fitness, were associated with
reduced rates of cardiovascular disease (CVD) and all-cause mortality (4;33;34). Also, an
increasing number of experimental studies showed disease risk factors or health-related
fitness measures to be significantly improved in sedentary adults as a result of adherence to
a program of regular walking or other moderate-intensity activity (35-37). During this time,
a team of Canadian exercise scientists organized two major international conferences on
Exercise, Fitness and Health (38) and Physical Activity, Fitness and Health (39). For both
conferences, the goal was to understand the relationship of physical activity and fitness to
major health outcomes, develop a conceptual model for these relationships, and formulate a
consensus statement. These conferences and publications provided an excellent resource for
the developing consensus that a physically inactive lifestyle is a major contributor to poor
health outcomes throughout the lifespan.
Physical Activity Guidelines Advisory Committee Report D–20
Part D. Background
In 1992, in light of the mounting evidence that a sedentary lifestyle significantly increased
the risk of CHD morbidity and mortality, the AHA made sedentary lifestyle its fourth major
CHD risk factor, joining cigarette smoking, hypertension, and hypercholesterolemia (40).
This statement was the first formal recognition by the AHA that physical inactivity was a
major independent risk factor for atherosclerotic heart disease and that physical activity
could play a role in both primary and secondary prevention of CHD. This document went
beyond recognizing just the benefits of exercise for heart disease to stating that people of all
ages could benefit from a regular exercise program. It noted that activities such as walking,
hiking, swimming, cycling, tennis, and basketball were especially beneficial if performed at
50% or more of a person’s work capacity and that even low-intensity activities performed
daily could have some long-term health benefits. This statement has been updated over the
years by the AHA but without major changes in the key statements made in 1992; the most
recent update was published in 2003 (41).
Given the influential nature of official position statements or recommendations by the AHA
on heart disease prevention and treatment practices by the medical community in the United
States, the elevation of inactivity to a major CHD risk factor brought substantial attention to
the importance of a physically active lifestyle. Although this statement indicated the general
nature of the activity that should be performed to help maintain good health, it lacked
specific details regarding program design and implementation. However, it did indicate that
intensities lower than that generally promoted in the past could provide health benefits.
In 1993, the year following the AHA statement recognizing inactivity as a major CHD risk
factor, the CDC in collaboration with the ACSM, began developing a document that would
provide specific recommendations about the profile of physical activity that should be
performed to promote good health. To develop this statement, an expert panel was appointed
that consisted of epidemiologists, exercise physiologists, public health professionals, and
health psychologists. The panel was charged with developing a statement grounded in solid
science that would clearly communicate its key messages to the public and provide a
program that could be performed by a large segment of the general public with a minimal
increase in risk. It took 2 years of work by the panel before Physical Activity and Public
Health: A Recommendation from the Centers for Disease Control and Prevention and the
American College of Sports Medicine was released to the public in 1995 (8). These first
public health guidelines on physical activity and health were the culmination of a decade of
work that began in 1984 with the CDC Workshop on the Epidemiological and Public Health
Aspects of Physical Activity and Exercise.
The approach to physical activity for health taken by these ”public health” guidelines was
quite different than prior guidelines primarily based on the “exercise training” or “clinical”
paradigm. The primary recommendation was that “Every American adult should accumulate
30 minutes or more of moderate-intensity physical activity on most, preferably all, days of
the week.” Because many of the prior recommendations had primarily advocated vigorousintensity activity, having moderate-intensity activity as the key recommendation (even
though prior guidelines based on vigorous-intensity exercise were recognized as still
Physical Activity Guidelines Advisory Committee Report D–21
Part D. Background
effective) raised many questions by exercise scientists and practitioners. The idea that
substantial health benefits could be derived from brisk walking was not appreciated by many
fitness advocates, but this recommendation was based on data from a variety of
epidemiologic and experimental studies. Even more controversial was the idea that the
activity each day did not need to be performed continuously for at least 30 minutes, but
could be accumulated throughout the day in bouts of 8 to 10 minutes. For many years, the
idea that the activity needed to be continuous to be effective had been promoted in programs
such as “Aerobics” (42) but without any scientific evaluation. In retrospect, the
recommendation for accumulated bouts appears to have been correct. However, in 1995, the
published scientific data supporting this concept was quite limited, and remains so today.
Only several experimental studies had directly compared the effects of continuous exercise
bouts versus exercise accumulated through bouts of 8 to 10 minutes duration (43-45), and
the nature of data collection in epidemiologic studies made the evaluation of the
accumulation concept difficult, at best, to evaluate.
Following close on the heels of the CDC/ACSM report, the National Institutes of Health
(NIH) convened a consensus conference on “Physical Activity and Cardiovascular Health”
(46). The charge to this nonfederal, non-advocate 13-member panel representing cardiology,
psychology, exercise physiology, nutrition, pediatrics, public health and epidemiology was
“to provide physicians and the general public with a responsible assessment of the
relationship between physical activity and cardiovascular health.” During the 3-day
conference, the panel listened to reports from 27 scientists on the relationship between
physical activity and cardiovascular health, had open discussions with the presenting
scientists and others in attendance, and held closed deliberations to formulate their
recommendations. The draft recommendations were shared with conference participants and
conflicting views were resolved and a final document produced.
The panel concluded that: (1) most Americans have little or no physical activity in their
daily lives; (2) accumulating evidence indicates that physical inactivity is a major risk factor
for cardiovascular disease; (3) moderate levels of physical activity confer significant health
benefits; (4) all Americans should engage in regular physical activity at a level appropriate
to their capacity, needs and interests; and (5) children and adults should set a goal of
accumulating at least 30 minutes of moderate intensity physical activity on most, and
preferably all, days of the week.
The panel also recognized that a greater amount and/or intensity of activity than the
recommended minimum would provide greater health benefits for most people (i.e., dose
response) and that cardiac patients should integrate increased physical activity into a
comprehensive program of risk reduction. Thus, the panel made recommendations highly
consistent with the CDC/ACSM working group in that it emphasized performing moderateintensity physical activity (using brisk walking as a benchmark) on most or all days for at
least 30 minutes per day, and noted the activity could be accumulated in bouts of at least 8 to
10 minutes duration. It also recognized that its recommendation was a minimum, and greater
health benefits were achievable by performing greater amounts of activity or through
Physical Activity Guidelines Advisory Committee Report D–22
Part D. Background
“vigorous exercise.” In other words, the prior recommendations of vigorous exercise
performed for 20 to 30 minutes 3 days per week still applied.
At the same time the NIH was producing its consensus panel report, the World Health
Organization also issued a report on the health benefits of regular activity (47). The major
recommendations in this document were very consistent with recommendations made by the
CDC/ACSM working group and the NIH consensus panel, namely that a target for all adults
should be 30 minutes or more of moderate-intensity physical activity on most days. The
WHO report also stated that daily physical activity should be the cornerstone for a healthy
lifestyle throughout the lifespan; that more vigorous exercise, such as slow jogging, cycling,
field and court games, and swimming, could provide additional health benefits; and that
people with disabilities or chronic disease had a great deal to benefit from an individualized
activity program. While recognizing that the responsibility for personal health decisions
ultimately lies with the individual and family, policy recommendations for increasing
physical activity were included in the report as well for major government organizations.
The CDC/ACSM, NIH, and WHO reports on physical activity and health, all published in
1995 and 1996, set the stage for the publication of Physical Activity and Health: A Report of
the Surgeon General in 1996 (11). This report was commissioned by the Secretary of Health
and Human Services in 1994 and authorized the CDC to be the lead agency for its
development with collaboration from a number of federal organizations, especially the
President’s Council on Physical Fitness and Sports and the NIH. Non-government
collaborating organizations included the ACSM, AHA, and the American Association of
Health, Physical Education, Recreation and Dance. This was an extensive undertaking, and
approximately 195 people contributed to writing, editing, reviewing, and publishing the
report.
The stated goal of the Surgeon General’s report was to summarize the existing literature on
the role of physical activity in preventing disease and on the status of interventions to
increase physical activity. It provided an historical background on the relation of physical
activity to health, including the evolution of physical activity guidelines, looked at patterns
and trends of physical activity in different populations in the United States, and described
various projects to promote increased physical activity in youth and adults. It also
summarized information on acute and chronic physiological responses to exercise and
provided a systematic review of the effects of physical activity on major health outcomes.
The report grew out of an emerging consensus among investigators and providers working
in exercise science, epidemiology, public health, clinical medicine, health psychology, and
education that the high prevalence of sedentary behavior among the American population
was having a significant negative health impact, that a moderate amount and intensity of
physical activity in this sedentary population could provide important health benefits, and
that innovative, long-term programs were needed to reverse the continuing downward trend
in physical activity.
Physical Activity Guidelines Advisory Committee Report D–23
Part D. Background
The key recommendation from the Surgeon General’s report was that people of all ages
could improve the quality of their lives through a lifelong practice of moderate-intensity
physical activity: “A regular, preferably daily, regimen of at least 30 to 45 minutes of brisk
walking, bicycling, or even working around the house or yard will reduce the risk of
coronary heart disease, hypertension, colon cancer and diabetes.” A second key message
was that “more is better.” People already performing a moderate level of activity would
benefit even more by increasing the intensity and/or duration of their activity. Both the
CDC/ACSM report and the report by the Surgeon General have been cited frequently in the
professional literature on physical activity and health, and the key recommendations, usually
with no or only minor modifications, have been adopted by national agencies in a number of
other countries.
To help assess the information available on the dose of physical activity needed for specific
health outcomes, an international “consensus symposium” was held at Hockley Valley,
Ontario, Canada in 2000 (48). The goal of this evidence-based symposium was to provide a
comprehensive review of the existing science relating physical activity dose to health and to
make specific recommendations regarding physical activity dose. The major conclusion
regarding the dose-response relation for specific outcomes was that the available data were
still inadequate to define any precise relation. However, the consensus panel did endorse the
recommendations made in the CDC/ACSM report (8) and the Surgeon General’s report (11).
The Institute of Medicine Report
In 2002, the Institute of Medicine (IOM) published a report primarily focusing on
macronutrient intake and energy intake and expenditure. The report developed estimates of
daily intake that are compatible with good nutrition throughout the life span and that may
decrease the risk for chronic disease (49). The preparation of this report by the IOM, a
private nonprofit organization and component of the National Academy of Sciences, was
funded by HHS, the US Department of Agriculture (USDA), the US Department of Defense,
and Health Canada. The panel considered the level of macronutrient, and thus caloric intake,
consistent with good health and the caloric expenditure needed to keep people in a healthy
weight range, defined as a body mass index (BMI) of 18.5 to 25.0 kg/m2. For people to
achieve these goals, the panel concluded the following regarding physical activity:
“Physical activity promotes health and vigor. Cross-sectional data from a doubly labeled
water database were used to define a recommended level of physical activity, based on the
physical activity level (PAL) associated with a normal body mass index (BMI) range of
18.5 to 25 kg/m2. In addition to the activities identified with a sedentary lifestyle, an average
of 60 minutes of daily moderate intensity physical activity (e.g., walking/jogging at 3 to 4
miles/hour) or shorter periods of more vigorous exertion (e.g., jogging for 30 minutes at 5.5
miles/hour) was associated with a normal BMI and therefore is recommended for normalweight individuals. This amount of physical activity leads to an ‘active’ lifestyle,
corresponding to a PAL greater than 1.6 (see Chapter 5). Because the Dietary Reference
Physical Activity Guidelines Advisory Committee Report D–24
Part D. Background
Intakes are provided for the general healthy population, recommended levels of physical
activity for weight loss of obese individuals are not provided.” (p.880).
Upon the release of this report, many in the press, general public, and health professions
considered that the report had articulated a significant change in physical activity
recommendations for health, with the target now being 60 minutes of moderate-intensity
activity daily rather the 30 minutes or more that had been promoted since 1995. However, it
is very important to understand that the prior recommendations by CDC, ACSM, NIH, and
HHS were based primarily on the amount of physical activity shown to be consistent with
lower morbidity and mortality rates from selected chronic diseases and all-cause mortality,
and not on the amount for achieving an optimal BMI of 18.5-25.0 kg/m2, which was the
major goal of the IOM report. Also, in the IOM report, the 60-minute recommendation was
made in order to achieve all the identified health benefits fully, while in the other reports,
the 30 or more-minute recommendation was considered a minimum. The other reports
acknowledged that more exercise would bring additional benefits. As with the prior reports,
the IOM document indicated that activity could be accumulated throughout the day and did
not need to be performed only in a single session.
A key difference in the data considered during the formulation of the IOM recommendation
versus other previous physical activity recommendations was the IOM panel’s emphasis on
doubly-labeled water studies. Combining data from available doubly-labeled water studies,
the panel estimated the total daily energy expenditure of men and women who had a BMI of
18.5 to 25.0 kg/m2. They determined that these subjects had an average PAL of about 1.75.
The panel then took the PAL of people considered to be sedentary (1.25) and that of people
considered to be of normal weight (1.75) then calculated the difference in PAL between
people who were sedentary and those who were normal weight and converted this to
minutes per day of moderate-intensity activity. Not taken into this consideration was the fact
that the PAL for the subjects in the doubly-labeled water studies who were overweight or
obese was not 1.25 but in the 1.59 to 1.85 range (50). These cross-sectional data do not deal
with the question of how much added exercise will produce a meaningful change in body
weight.
The IOM selection of a target activity level of 60 minutes per day or a PAL of 1.6 or greater
to maintain optimal body weight is somewhat less than the target PAL of 1.75 in the 1998
report by the World Health Organization, Obesity: Preventing and Managing the Global
Epidemic (51). In this extensive report, the authors stated that analyses of more than 40
national physical activity studies worldwide show a significant relationship between the
average BMI of adult men and their PAL, with the likelihood of becoming overweight being
substantially reduced at PALs of 1.8 or above. For women, the PAL associated with a
healthy weight was approximately 1.6. Therefore, the WHO report suggested “that people
should remain physically active throughout life and sustain a PAL of 1.75 or more in order
to avoid excessive weight gain” (p.124).
Physical Activity Guidelines Advisory Committee Report D–25
Part D. Background
In 2002, an international group of scientists with expertise in physical activity, nutrition,
energy balance and obesity held a consensus meeting convened by the International
Association for the Study of Obesity to assess “how much physical activity is enough to
prevent unhealthy weight gain” (52). Part of their conclusion was that, “The current physical
activity guideline for adults of 30 minutes of moderate intensity activity daily, preferably all
days of the week, is of importance for limiting health risks for a number of chronic diseases,
including coronary heart disease and diabetes. However, for the prevention of weight gain or
regain this guideline is likely to be insufficient for many individuals in the current
environment. There is compelling evidence that prevention of weight regain in formally
obese individuals requires 60 to 90 minutes of moderate intensity activity or lesser amounts
of vigorous activity. Although definitive data are lacking, it seems likely that moderate
intensity activity of approximately 45 to 60 minutes per day or 1.7 PAL is required to
prevent the transition to overweight or obesity” (page 101). This consensus statement
recognized that the amount of physical activity associated with lower chronic disease
mortality rates is very likely less than that needed in the current environment to prevent
unhealthy weight gain or regain in many adults.
Dietary Guidelines for Americans, 2005
Every 5 years, the USDA and HHS are required by the US Congress to prepare Dietary
Guidelines for Americans. The Guidelines published in 1995 and 2000 recognized that a
physically active lifestyle should be maintained for optimal health, but no specific guideline
focused on prevention of weight gain or weight loss. For example, in 2000 the
recommendations were highly consistent with the 1995 CDC/ACSM report directed to
improving general health status: “Aim to accumulate at least 30 minutes (adults) or
60 minutes (children) of moderate intensity activity on most days of the week, preferably
daily. If you already get 30 minutes of physical activity daily, you can gain even more health
benefits by increasing the amount of time you are physically active or by taking part in more
vigorous activities. No matter what activity you choose, you can do it all at once, or spread it
out over two or three times per day” (53), p.10.
The 2005 Dietary Guidelines for Americans structured the physical activity
recommendations to separate advice about chronic disease prevention from advice about the
amount of physical activity required for the prevention of unhealthy weight gain or regain or
achieving weight loss in adults (54). They took the generally accepted position that a variety
of health benefits are derived from at least 30 minutes of moderate-intensity exercise on
most days, and separated this recommendation from the less well documented and
understood recommendations regarding the amount of physical activity required to prevent
unhealthy weight gain or regain and weight loss. The physical activity recommendations
needed to help manage body weight were adopted in large part from the 2002 IOM report
(49), which had primarily considered cross-sectional data from doubly-labeled water studies
of energy expenditure (55). To help adults manage body weight and prevent gradual
unhealthy weight gain, the Guidelines recommended approximately 60 minutes of
moderate/vigorous activity on most days of the week (while not exceeding calorie
Physical Activity Guidelines Advisory Committee Report D–26
Part D. Background
requirements). To help adults lose weight and to sustain weight loss, the Guidelines
recommended at least 60 to 90 minutes of daily moderate-intensity physical activity daily
(while not exceeding calorie requirements). These two recommendations regarding weight
gain prevention and weight loss received the most attention and contributed to some
confusion among the public.
2007 American College of Sports Medicine and American Heart
Association Physical Activity Recommendations
In 2002, the ACSM and CDC organized an expert panel to consider whether the 1995
CDC/ACSM physical activity and public health recommendations needed to be updated (8).
Key reasons for this consideration included new scientific evidence since 1995 relating
physical activity to health, physical activity recommendations by various organizations in
the interim that appeared to be in conflict with the 1995 recommendations, and
communications issues related to certain terminology used in the 1995 report. The panel
decided that an update would be of value to health professionals and the public, and two
writing groups were formed, one to prepare recommendations for adults (18 to 65 years) and
another for older adults (older than 65 years). The purpose of these reports was to update
and clarify the 1995 recommendations on the types and amounts of physical activity needed
by healthy adults and older adults to improve and maintain health. These groups reviewed
advances in pertinent physiologic, epidemiologic, and clinical scientific data, including
primary research articles and reviews published since the original recommendation was
issued in 1995.
The writing groups prepared the two manuscripts, intending that the recommendations
would represent an update from CDC and ACSM. However, after extensive review at CDC
and HHS, it was decided that because physical activity recommendations for adults had been
published as part of the 2005 Dietary Guidelines for Americans that CDC should not issue
additional physical activity recommendations. ACSM representatives then asked the AHA to
participate in issuing the updated recommendations, and the two sets of recommendations
were published in 2007 (56;57). No major changes were made in the recommendations
either for adults or older adults but a number of features about the type and amount of
activity most likely to provide various benefits were clarified. Also, issues regarding the role
of physical activity in body weight management were addressed and resistance exercise was
made part of the core recommendation for all adults.
Primary recommendations for adults included the following:
• To promote and maintain health, all healthy adults aged 18 to 65 years need
moderate-intensity aerobic (endurance) physical activity for a minimum of 30
minutes on 5 days each week or vigorous-intensity aerobic physical activity for a
minimum of 20 minutes on 3 days each week. Combinations of moderate- and
vigorous-intensity activity can be performed to meet this recommendation. For
example, a person can meet the recommendation by walking briskly for 30 minutes
Physical Activity Guidelines Advisory Committee Report D–27
Part D. Background
twice during the week and then jogging for 20 minutes on 2 other days.
Moderate-intensity aerobic activity, which is generally equivalent to a brisk walk and
noticeably accelerates the heart rate, can be accumulated toward the 30-minute
minimum by performing bouts each lasting 10 or more minutes. Vigorous-intensity
activity is exemplified by jogging, and causes rapid breathing and a substantial
increase in heart rate.
• In addition, every adult should perform activities that maintain or increase muscular
strength and endurance a minimum of 2 days each week. Because of the doseresponse relation between physical activity and health, persons who wish to further
improve their personal fitness, reduce their risk for chronic diseases and disabilities
or prevent unhealthy weight gain may benefit by exceeding the minimum
recommended amounts of physical activity.
The recommendations for older adults are very similar to the updated ACSM/AHA
recommendations for adults, but have several important differences. For example, the
recommended intensity of aerobic activity takes into account the older adult’s aerobic
fitness, activities that maintain or increase flexibility are recommended, and balance
exercises are recommended for older adults at risk of falls. In addition, older adults are
encouraged to have an activity plan for achieving recommended physical activity that
integrates preventive and therapeutic recommendations. The promotion of physical activity
in older adults places more emphasis on moderate-intensity aerobic activity, musclestrengthening activity, reducing sedentary behavior, and risk management.
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Physical Activity Guidelines Advisory Committee Report D–33
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Part E:
Integration and Summary
of the Science
Introduction
The PAGAC’s final step in developing this report was to integrate and summarize the key
conclusions and supporting data that each subcommittee prepared and presented in their
chapters (Part G: The Science Base). Each chapter in Part G provides a review of the
scientific literature on physical activity and a selected health outcome or population, and the
chapters’ conclusions are supported by original publications cited in extensive reference
lists.
Each subcommittee’s major conclusions were reviewed and accepted by the PAGAC during
its final meeting on February 28-29, 2008. Because much of the scientific review by
PAGAC members and consultants was organized around specific health outcomes, the
PAGAC decided that it needed, where possible, to integrate key findings for these various
outcomes into general statements about the scientific support for health-related benefits of
physical activity. This chapter provides the results of the Committee’s summary and
integration process. Using a plan outlined below, PAGAC members first summarized the
type and strength of evidence for their major conclusions. This evidence is presented in a
series of tables on pages E-4 to E-22
The Committee then integrated the evidence and conclusions by developing responses to a
set of questions that are typical of those raised by health and fitness professionals and the
general public about the scientific evidence on a number of issues about physical activity
and health. These responses are supported by the information provided in the chapters in
Part G: The Science Base. The questions and answers can be found on pages E-22 to E-35.
Summarizing the Evidence
During the final PAGAC meeting, each subcommittee chair was asked to prepare a
summary of key findings for discussion by the Committee, using the plan outlined in
Table E.1. Each subcommittee’s summary report was to include information on the type and
magnitude of evidence reviewed, the strength of the evidence, characteristics of the physical
activity most likely to produce the outcome, any evidence of a dose response, and any
evidence that being sedentary puts a person at high risk (see Table E.1A). To determine the
overall strength of the evidence for major health and fitness outcomes and to evaluate the
issue of dose response for these outcomes, subcommittees considered the types of studies
that addressed each specific question (see Table E.1B) and the general quality of these
Physical Activity Guidelines Advisory Committee Report E–1
Part E. Integration and Summary of the Science
studies (e.g., design, sample size, statistical power, measurement methods, follow-up,
adherence). For each major outcome, but not for each study, subcommittee chairs were
asked to assign a strength of evidence — strong, moderate, weak — based on the evidence
they included in their review chapters (see Table E.1C). Also, in assigning the strength of
the evidence, subcommittees included factors that support a causal relation between physical
activity and a specific outcome, such as evidence of favorable changes in biomarkers
considered to be in the causal pathway or a significant dose-response relation.
Table E.1. Process for Summarizing the Science
A. Instructions to Subcommittee Chairs
• Only major outcomes to be considered in summary
• Types and amounts of evidence available for this outcome
• Strength of the evidence (strong, moderate, weak)
• Based on current science characteristics of activity most likely to produce this outcome
o Type: aerobic, resistance, other
o Intensity: light, moderate, vigorous (include comment on walking)
o Frequency: times per week
o Duration; minutes per day/week
o Amount: MET-hours per week (or other measure if appropriate)
o Accumulation: multiple bouts during day
• Any evidence of dose response for amount or intensity
• Any evidence that being very sedentary puts person at highest risk. If possible, quantify.
B. Types of Evidence
• Type 1
o Randomized controlled trials (RCT) (or meta-analyses) without major limitations
• Type 2
o 2a – RCTs (or meta-analyses) with important limitations
o 2b – Non-randomized clinical trials
• Type 3
o 3a – Well-designed prospective cohort studies and case-control studies
o 3b – Other observational studies, e.g., weak prospective cohort studies or case-control
studies; cross-sectional studies or case series
• Type 4
o Inadequate, very limited, or no data in population of interest. Anecdotal evidence or no/little
clinical experience
C. Strength of the Evidence
• Strong, consistent across studies and populations
• Moderate or reasonable, reasonably consistent
• Weak or limited, inconsistent across studies and populations
Physical Activity Guidelines Advisory Committee Report E–2
Part E. Integration and Summary of the Science
While deciding on a plan for summarizing the evidence, PAGAC members discussed the
possible use of an evidence-based rating system designed for the development of evidencebased guidelines for medical practice, such as those adopted by the American College of
Cardiology and the American Heart Association in 2006 (1). This approach was dismissed
for several reasons. First, a full application of these methodologies did not apply to the
PAGAC mission, which was to review and evaluate the science, not to provide practice
guidelines or recommendations. Second, Committee members were concerned that the
criteria used to evaluate evidence for the safe and effective use of medical interventions or
therapies (such as drugs or medical devices) developed to treat disease are not readily
applicable for evaluating the effects of lifestyle changes on chronic disease prevention,
where standards of experimental design such as double blinding are exceptionally difficult,
if not impossible.
The Committee also recognized that because of logistical, cost, and ethical issues, few RCTs
have been conducted to link physical activity to reduced rates of chronic diseases. This
situation is not very different from that linking other health-related behaviors to the
prevention of clinical outcomes. A good example is cigarette smoking. For obvious ethical
reasons, no one has conducted an RCT of the impact of starting cigarette smoking on health
outcomes, such as lung cancer, chronic obstructive pulmonary disease, or coronary heart
disease. A similar situation exists for the relation between saturated fat or trans-fatty acid
intake and the prevention of coronary heart disease. Yet, the weight of evidence is believed
to be so strong from observational studies that urging the public to stop smoking or reduce
their intake of saturated fat or trans-fatty acids are major components of national public
health campaigns. Similarly, data linking physical activity to lower rates of all-cause
mortality, coronary heart disease, stroke, and type 2 diabetes based on observational studies
are strong and, further, are supported by RCTs showing significant favorable effects on key
biomarkers for these conditions. The result of these deliberations by the PAGAC was the
development of the evidence rating criteria presented in Table E-1.
Selected PAGAC members were then asked to integrate the main conclusions from these
subcommittee summaries under the headings of youth, adults, older adults, understudied
populations, and adverse events. These summary conclusions were presented to PAGAC
members, and each set of conclusions was discussed and edited. A final set of conclusions
was developed using a consensus process.
Following the PAGAC meeting on February 28-29, 2008, the Committee prepared the
following information, which summarizes the major conclusions of each committee. The
sum of the evidence provided here for a wide range of health and fitness outcomes strongly
supports the value of being physically active versus being sedentary throughout the lifespan.
Physical Activity Guidelines Advisory Committee Report E–3
Part E. Integration and Summary of the Science
Health Outcome: All-Cause Mortality
Types of studies?
Type 3a – extensive
What is the nature of the association of physical activity (PA) with All-Cause Mortality?
There is a clear inverse relationship between PA and all-cause mortality.
Strength of evidence: Strong
What is the effect size?
There is about a 30% risk reduction across all studies, comparing most with least active subjects.
Strength of evidence: Strong
Is there any evidence for an effect of sex, age, or race/ethnicity?
There is evidence that this association exists for both men and women, as well as for people both
younger than age 65 years or 65 years of age and older. There is also evidence that this
association exists for different race/ethnic groups.
Strength of evidence: Sex = Strong, <65 & 65+ years = Strong, Race/Ethnicity = Reasonable
Is there a dose-response effect?
There is an inverse dose-response relation for total volume of PA (i.e., total energy expenditure).
The shape of the dose-response curve appears curvilinear in that larger risk decreases are seen
at the lower end of the physical activity spectrum than at the upper end. There are limited data on
an inverse dose-response relation for intensity, which is independent of its contribution to the total
volume of PA (i.e., limited data suggest that vigorous physical activity may be associated with
further risk reduction compared with moderate-intensity activity when the total volume of energy
expenditure is the same).
Strength of evidence: Volume = Strong, Intensity = Limited
What is an effective PA dose regarding mode, duration, intensity, and frequency that is
supported by the evidence? (Strength of evidence in parentheses)
Data indicate at least 2 to 2.5 hours per week of moderate-to-vigorous physical activity are
needed to see significantly lower risk (Strong).
Data are primarily for aerobic leisure-time physical activity (LTPA) (Strong).
There are also specific data showing that walking at least 2 hours per week is associated with
significantly lower risk (Strong).
Some evidence also indicates that all activities count (Reasonable)
This amount — 2 to 2.5 hours per week of moderate-to-vigorous PA — does not represent a
threshold level for risk reduction. The data consistently support a “some is good; more is better”
message (Strong). Some data indicate that among populations where physical activity levels are
likely to be low (e.g., middle-aged and older women; older men), significantly lower mortality rates
are observed at levels less than 2 to 2.5 hours per week of moderate-to-vigorous PA (Limited).
Physical Activity Guidelines Advisory Committee Report E–4
Part E. Integration and Summary of the Science
Health Outcome: All-Cause Mortality (continued)
What is the evidence on accumulation? (Strength of evidence in parentheses)
No direct data on multiple short bouts versus one long bout.
However, indirect data come from epidemiologic studies showing an inverse association with total
volume, where the PA is likely to be accumulated from activities of different (but unknown)
durations (Reasonable).
What other unique comments should be made about the evidence of PA with this health
outcome? (Strength of evidence in parentheses)
The association of PA and all-cause mortality is independent of body mass index (Strong); this
association is seen regardless of whether persons are normal weight, overweight, or obese
(Reasonable).
Health Outcome: Cardiorespiratory Health
Types of studies?
Type 3a – extensive for coronary heart disease (CHD), cardiovascular disease (CVD), and stroke
Type 1 – extensive for hypertension, atherogenic dyslipidemia, and cardiorespiratory fitness
What is the nature of the association of PA with Cardiorespiratory Health?
There is a clear inverse relation between PA and cardiorespiratory health (CHD, CVD, stroke,
hypertension, and atherogenic dyslipidemia).
The data imply relations with physical activity volume, with less information about intensity and
none for frequency and duration per session for CVD clinical events.
Physical activity improves cardiorespiratory fitness. Fitness has direct dose-response relations
between intensity, frequency, duration, and volume. There is limited evidence for an accumulation
effect.
Strength of evidence: Strong
What is the effect size?
There is a 20% to 35% lower risk for CVD, CHD, and stroke.
Participation in aerobic activity improves cardiorespiratory fitness in a dose-response fashion
according to the frequency, duration, intensity, and total volume of the exposure. Percentage
increases are highly dependent on fitness levels at baseline, sex, and age of the study population,
and range from 4.5% with low-volume brisk walking to close to 20% with high-volume, highintensity exercise training.
Strength of evidence: Strong
Is there any evidence for an effect of sex, age, race/ethnicity?
These associations exist for both men and women and individuals of all ages. There is no evidence
for sex-specific, age-specific, or race/ethnic specific effects when volume is the exposure rather
than relative intensity.
Strength of evidence: Sex = Strong, Age = Strong, Race/Ethnicity = Reasonable
Physical Activity Guidelines Advisory Committee Report E–5
Part E. Integration and Summary of the Science
Health Outcome: Cardiorespiratory Health (continued)
Is there a dose-response effect?
There is a dose-response relation for CVD and CHD. There appears to be an L-shaped relation for
stroke. The relations are all most closely related to volume, with less information about intensity
and none for frequency and duration of sessions. Minutes per week is a less powerful parameter of
dose response than is volume per week (kilocalories per week; MET-minutes per week).
Physical activity improves cardiorespiratory fitness. For fitness there are direct dose-response
relations between intensity, frequency, duration, and volume. There is mixed evidence for an
accumulation effect.
Strength of evidence: Strong
What is an effective physical activity dose regarding mode, duration, intensity, and
frequency that is supported by the evidence? (Strength of evidence in parentheses)
At least 800 MET-minutes per week or 12 miles per week (moderate and/or vigorous); includes
specific data on brisk walking at least 2 hours per week (Strong). Data are primarily for aerobic
LTPA (Strong) on top of usual activities of daily living. Risk reductions start to be seen at levels
below 800 MET-minutes per week or 12 miles week (Reasonable).
What is the evidence on accumulation?
Very limited and mixed data available and mostly for cardiorespiratory fitness. Sparse evidence for
other CRH outcomes.
Strength of evidence: Limited
What other unique comments should be made about the evidence of PA with this health
outcome?
Notable lack of evidence for frequency, duration, and intensity effects on hard cardiorespiratory
health outcomes (CVD, CHD, and stroke) and lack of trial evidence for duration and intensity for
cardiovascular risk factors (hypertension and atherogenic dyslipidemia).
Health Outcome: Metabolic Health
Types of studies?
Type 2a (small body) and 3a (reasonable body) for type 2 diabetes
Type 3a/b (reasonable body) for metabolic syndrome
What is the nature of the association of PA with Metabolic Health?
There is a clear inverse relationship between PA and metabolic health, including the prevention of
type 2 diabetes and metabolic syndrome.
Strength of evidence: Strong
What is the effect size?
There is a 30% to 40% lower risk for type 2 diabetes and metabolic syndrome in at least
moderately active people compared to sedentary individuals.
Strength of evidence: Strong
Physical Activity Guidelines Advisory Committee Report E–6
Part E. Integration and Summary of the Science
Health Outcome: Metabolic Health (continued)
Is there any evidence for an effect of sex, age, race/ethnicity?
This association exists for both men and women, as well as for older and younger persons. There
is reasonable evidence to show the association exists for different race/ethnic groups.
Strength of evidence: Sex = Strong, Age = Strong, Race/Ethnicity = Reasonable
Is there a dose-response effect?
There is an inverse dose-response association between volume of PA and the development of
metabolic syndrome as well as the development of type 2 diabetes.
Strength of evidence: Reasonable
What is an effective PA dose regarding: mode, duration, intensity, and frequency that is
supported by the evidence? (Strength of evidence in parentheses)
Data indicate at least 120 to 150 minutes per week of moderate-to-vigorous PA is needed to see
significantly lower risks (Strong). Data are primarily for aerobic LTPA (Strong). Risk reductions start
to be seen at levels below the 120 to 150 minutes per week level of PA (Reasonable).
What is the evidence on accumulation?
There are limited data on accumulation.
What other unique comments should be made about the evidence of PA with this health
outcome?
There is limited evidence that PA helps to control HbA1c levels.
There is very limited evidence that PA helps to prevent gestational diabetes.
Health Outcome: Energy Balance
Types of studies?
Weight maintenance (less than 3% change in body weight):
Type 1, 2, 3a
Weight loss (at least 5% loss of body weight):
Type 1
Weight maintenance following weight loss:
Type 2
Abdominal obesity:
Type 1, 2
Physical Activity Guidelines Advisory Committee Report E–7
Part E. Integration and Summary of the Science
Health Outcome: Energy Balance (continued)
What is the nature of the association of PA with Energy Balance? (Strength of evidence in
parentheses)
Weight maintenance (less than 3% change in weight):
There is a favorable and consistent effect of aerobic PA on achieving weight maintenance (Strong).
The evidence is less consistent for resistance training, in part, because of the compensatory
increase in lean mass (Moderate), and the smaller volumes of exercise employed.
Weight loss (at least 5% loss of weight):
The amount of weight lost due to PA (alone) is dependent on the volume of activity, and few
studies have used a volume of PA large enough to achieve a 5% weight loss. If an isocaloric diet is
maintained throughout the PA intervention, weight loss is similar to what is observed for dietary
interventions and clearly exceeds 5% (Strong).
Weight maintenance following weight loss:
PA promotes less weight regain after a period of significant weight loss (Moderate).
Abdominal obesity:
A decrease in total abdominal adiposity and intra-abdominal adiposity is associated with aerobic
PA (Moderate to Strong). The effect is less well described for resistance training (Weak).
What is the effect size? (Strength of evidence in parentheses)
Weight maintenance (less than 3% change in weight):
Aerobic PA has a consistent effect on achieving weight maintenance (Strong); resistance training
has a moderate effect (Limited).
Weight loss (at least 5% loss of weight):
PA alone has no effect on achieving a 5% weight loss, except at very large volumes of PA or when
an isocaloric diet is maintained throughout the PA intervention (Strong).
Weight maintenance following weight loss:
Aerobic PA has a reasonably consistent effect on weight maintenance following weight loss
(Moderate).
Abdominal obesity:
Aerobic PA has a consistent effect on total abdominal adiposity and a smaller effect on intraabdominal adiposity (Strong). Resistance training has a small and less consistent effect on total
abdominal and intra-abdominal adiposity (Limited).
Is there any evidence for an effect of sex, age, race/ethnicity?
There is some evidence that the amount of physical activity needed to maintain a constant weight
differs between men and women and increases with age. However, the evidence is not sufficient to
recommend differential physical activity regimens based on sex or on age alone.
The paucity of literature, particularly of the stronger longitudinal cohort or randomized controlled
intervention study designs, makes it unwise to draw conclusions as to whether the physical activity
recommendation should differ by racial/ethnic or socioeconomic status groups.
Strength of evidence: Sex = Weak, Age = Weak, Race/Ethnicity = Weak
Physical Activity Guidelines Advisory Committee Report E–8
Part E. Integration and Summary of the Science
Health Outcome: Energy Balance (continued)
Is there a dose-response effect? (Strength of evidence in parentheses)
Weight maintenance (less than 3% change in body weight):
There is no evidence for a dose-response effect for PA and weight maintenance, as it has not been
specifically tested.
Weight loss:
There is a clear, consistent dose-response effect of aerobic PA on weight loss (Strong).
Weight maintenance following weight loss:
A dose-response is present — those performing the larger volumes of aerobic PA had less weight
regain (Moderate).
Abdominal obesity:
Larger, well-designed studies report a dose-response relationship for aerobic PA related to
abdominal obesity measures (Moderate).
What is an effective PA dose regarding mode, duration, intensity, and frequency that is
supported by the evidence? (Strength of evidence in parentheses)
Weight maintenance (less than 3%):
The optimal amount of physical activity needed for weight maintenance over the long-term is
unclear. However, there is clear evidence that physical activity provides benefit for weight stability.
There is a great deal of inter-individual variability with physical activity and weight stability, and
many persons may need more than 150 minutes of moderate-intensity activity per week to
maintain weight. Data from recent well-designed RCTs lasting up to 12 months indicate that
aerobic physical activity performed to achieve a volume of 13 to 26 MET-hours per week is
associated with approximately a 1% to 3% weight loss, which is generally considered to represent
weight stability. Thirteen MET-hours per week is approximately equivalent to walking at 4 miles per
hour for 150 minutes per week or jogging at 6 miles per hour for 75 minutes per week.
Weight loss (at least 5% weight loss):
There are clear, consistent data that a large volume of physical activity is needed for weight loss in
the absence of concurrent dietary changes. Physical activity equivalent to 26 kilocalories per
kilogram (1,560 MET-minutes) or more per week is needed for weight loss of 5% or greater
(Moderate); less amounts of weight loss are seen with smaller amounts of physical activity. This
relatively high volume of physical activity is equivalent to walking about 45 minutes per day at 4
miles per hour or about 70 minutes per day at 3 miles per hour, or jogging 22 minutes per day at 6
miles per hour.
Weight maintenance following weight loss:
PA equivalent to 30 kilocalories per kilogram per week or more. This is equivalent to walking about
50 minutes per day at about 4 miles per hour or 80 minutes per day at about 3 miles per hour, or
jogging for 25 minutes per day at 6 miles per hour (Moderate).
Physical Activity Guidelines Advisory Committee Report E–9
Part E. Integration and Summary of the Science
Health Outcome: Energy Balance (continued)
Abdominal obesity:
Aerobic physical activity in the range of 13 to 26 kilocalories per kilogram per week results in
decreases in total and abdominal adiposity that are consistent with improved metabolic function.
Thirteen MET-hours per week is approximately equivalent to walking at 4 miles per hour for 150
minutes per week or jogging at 6 miles per hour for 75 minutes per week. However, larger volumes
of physical activity (e.g., 42 kilocalories per kilogram per week) result in decreases in intraabdominal adipose tissue that are 3 to 4 times that seen with 13 to 26 kilocalories per kilogram per
week of physical activity.
What is the evidence on accumulation? (Strength of evidence in parentheses)
Weight maintenance (less than 3%):
Accumulation of energy expenditure due to PA is what is important to achieving energy balance*
(Strong). Accumulation of PA can be obtained in short multiple bouts or one long bout to meet PA
expenditure goals for weight maintenance (Moderate).
Weight loss (at least 5% weight loss):
There is evidence that accumulation of PA independent of distribution of PA bouts is what is
important for weight loss (Limited); however, it is difficult accumulate large volumes of PA without
concentrated bouts.
Weight maintenance following weight loss:
There is reasonable evidence that accumulation of PA independent of distribution of bouts is what
is important for weight stability following weight loss (Limited); however, it is difficult accumulate
large volumes of PA without concentrated bouts.
Abdominal obesity:
This has not been tested.
What other unique comments should be made about the evidence of PA with this health
outcome?
*NOTE: It is important to note that the role of energy intake (diet) must be considered in any
discussion of physical activity and weight control. Weight loss in excess of 5% can be achieved
with large volumes of physical activity. However, a more predictable weight loss occurs when
energy intake is held constant during a physical activity intervention.
Health Outcome: Musculoskeletal Health
Types of studies?
Bone:
Type 3a: fractures
Type 1, 2a: bone density
Joint:
Type 3a: prevention and/or promotion of osteoarthritis (OA)
Type 1: improvement of OA, rheumatoid arthritis (RA), and fibromyalgia
Muscular:
Type 1: muscle strength
Physical Activity Guidelines Advisory Committee Report E–10
Part E. Integration and Summary of the Science
Health Outcome: Musculoskeletal Health (continued)
What is the nature of the association of PA with Musculoskeletal Health? (Strength of
evidence in parentheses)
Bone:
There is an inverse association of PA with relative risk of hip fracture (Moderate) and vertebral
fracture (Weak). Increases in exercise training can increase, or minimize the decrease, in spine
and hip bone mineral density (BMD) (Moderate).
Joint:
In the absence of a major joint injury, there is no evidence that regular moderate PA promotes the
development of OA (Moderate). Participation in low/moderate levels of PA may provide a mild
degree of protection against the development of OA (Weak, Limited). Participation in moderateintensity, low-impact PA has disease-specific benefits (pain, function, quality of life, and mental
health) for people with OA, RA, and fibromyalgia (Strong). PA may delay the onset of disability in
people with OA (Weak).
Muscular:
Increases in exercise training enhance skeletal muscle mass, strength, power, and intrinsic
neuromuscular activation (Strong).
What is the effect size? (Strength of evidence in parentheses)
Bone:
Risk reduction of hip fracture is 36% to 68% at the highest level of PA (Moderate). The magnitude
of effect of PA on BMD is 1% to 2% (Moderate).
Joint:
Risk reduction of incident OA for various measures of walking ranges from 22% to 83% (Weak).
Among adults with osteoarthritis, pooled effect sizes (ES) for pain relief are small to moderate (ES
= 0.25 to 0.52); for function and disability ES are small (function ES = 0.14 to 0.49, disability ES =
0.32 to 0.46) (Strong).
Muscular:
The magnitude of the effect of resistance types of PA on muscle mass and function is highly
variable and dose-dependent (Strong).
Is there any evidence for an effect of sex, age, race/ethnicity? (Strength of evidence in
parentheses)
Bone:
There is evidence for a lower relative risk of hip fracture in older women and men; the evidence is
more consistent in women (Moderate). Benefits of PA on BMD have been found to occur in
premenopausal women, postmenopausal women, and adult men; the evidence is more consistent
in women (Moderate). Information on race and ethnic specificity is lacking.
Joint:
Female sex and older age are established risk factors for incident OA (Strong), the evidence for
race/ethnicity is equivocal (Weak). Male and female adults of any age with OA benefit from both
aerobic and resistance exercise (Strong). Women may have a bigger benefit from resistance
exercise, likely due to lower baseline muscular strength (Limited).
Physical Activity Guidelines Advisory Committee Report E–11
Part E. Integration and Summary of the Science
Health Outcome: Musculoskeletal Health (continued)
Muscular:
Benefits are similar in men and women and pervasive across the life span (Strong), although the
magnitude of the benefits may be attenuated in old age (Moderate). Information on race and ethnic
specificity is lacking.
Is there a dose-response effect? (Strength of evidence in parentheses)
Bone:
There is evidence of a dose-response association of PA with hip fracture risk (Moderate). Doseresponse effects have not been adequately tested for PA and BMD.
Joint:
High-level (elite, professional) athletes competing in high joint-loading sports (e.g., football, soccer,
track and field) may have an increased risk of hip/knee OA (Strong). Dose-response effects have
not been tested with regard to PA among adults with arthritis.
Muscular:
There is a dose-response with greatest gains in muscle mass and muscle strength experienced
with higher-intensity protocols (Strong).
What is an effective PA dose regarding mode, duration, intensity, and frequency that is
supported by the evidence? (Strength of evidence in parentheses)
Bone:
PA of 4 or more hours per week of walking, 2 to 4 hours per week of LTPA, 9 to 14.9 MET hours
per week of PA, and and1 hour per week of PA have been associated with a 36% to 41% lower
risk in hip fracture risk. Weight-bearing endurance and resistance types of PA (i.e., exercise
training) are effective in promoting increases in BMD (moderate-to-vigorous intensity; 3 to 5 days
per week; 30 to 60 minutes per session). Walking-only protocols found a benefit on spine BMD
(Moderate).
Joint:
For adults with arthritis, benefits in pain, function, and disability were noted with programs
averaging a total volume of 130 to 150 minutes per week: 30 to 60 minutes per session; 3 to 5
days per week; moderate intensity; low-impact (Strong). Both aerobic and muscle strengthening
activities improve joint function and reduce pain.
Muscular:
Progressive, high-intensity (60% to 80% of 1 repetition maximum [1RM]) muscle-strengthening
activities can preserve or increase skeletal muscle mass, strength, power, and intrinsic
neuromuscular activation (Strong).
Physical Activity Guidelines Advisory Committee Report E–12
Part E. Integration and Summary of the Science
Health Outcome: Musculoskeletal Health (continued)
What is the evidence on accumulation? (Strength of evidence in parentheses)
Bone:
The effects of accumulation have not been tested in humans.
Joint:
One study of fibromyalgia patients supports equal benefits (improved function, well-being, disease
activity) for 2 15-minute sessions per day and 1 30-minute session per day of moderate-intensity,
low-impact aerobic exercise (Limited).
Muscular:
The effects of accumulation have not been tested in humans.
What other unique comments should be made about the evidence of PA with this health
outcome?
Bone:
Individual RCTs support basic science findings that intensity of loading forces is a key determinant
of the skeletal response. Studies of laboratory animals also suggest that multiple, short bouts of PA
should have more favorable effects on bone than a single, longer bout of PA.
Joint:
Joint injuries and excess body mass are more important risk factors for incident OA than sports/PA
participation (Consistent, Strong).
Muscular:
Endurance types of PA do not increase muscle mass, but may attenuate the rate of loss with aging
and preserve function (Moderate).
Health Outcome: Functional Health
Types of studies?
Functional Health:
Type 3a, Type 1
Falls:
Type 1
What is the nature of the association of PA with Functional Health? (Strength of evidence in
parentheses)
Functional Health:
There is observational evidence that mid-life and older adults who participate in regular PA have
reduced risk of moderate/severe functional limitations and role limitations (Moderate to Strong). In
older adults with existing functional limitations, there is fairly consistent evidence that regular PA is
safe and has a beneficial effect on functional ability (Moderate); however, there is currently little or
no experimental evidence in older adults with functional limitations that PA maintains role ability or
prevents disability.
Physical Activity Guidelines Advisory Committee Report E–13
Part E. Integration and Summary of the Science
Health Outcome: Functional Health (continued)
Falls:
In older adults at risk for falls, there is consistent evidence that regular PA is safe and reduces risk
of falls (Strong).
What is the effect size? (Strength of evidence in parentheses)
Functional Health:
There is about a 30% risk reduction for the prevention or delay in function and/or role limitations
with PA (Moderate to Strong).
It is difficult to ascertain an effect size for the maintenance/improvements in functional ability due to
the variety of outcomes measured.
Falls:
Older adults who participate in regular PA have about a 30% lower risk of falls (Strong).
Is there any evidence for an effect of sex, age, race/ethnicity? (Strength of evidence in
parentheses)
The association exists for both men and women with respect to preventing and maintaining or
improving functional health and reducing risk of falls (Strong). The association exists for preventing
functional limitations in middle-aged and older adults (Strong); the association for maintaining or
improving functional heath is seen in older adults aged 65 years and older (Moderate); the
association with falls reduction is seen in older adults at increased risk for falls (Strong). There is
limited evidence to show an association exists for different race/ethnic groups for all outcomes
(Weak).
Is there a dose-response effect? (Strength of evidence in parentheses)
Functional Health:
There appears to be a dose-response effect for PA in preventing or delaying function and/or role
limitations, with greatest risk reduction seen with the highest levels of PA (Moderate). It is unclear
whether there is a dose-response effect for PA in maintaining or improving functional ability, as this
has not been tested.
Falls:
It is unclear whether there is a dose-response effect for PA in the reduction of falls in older adults,
as this has not been tested.
What is an effective PA dose regarding mode, duration, intensity, and frequency that is
supported by the evidence? (Strength of evidence in parentheses)
Prevention:
The most evidence of a dose response exists for walking activities (Strong); it is not possible at this
point to ascertain dose of PA due to the nature of the study designs.
Maintenance/Improvement:
Evidence exists for exercise programs that include periods of 30 to 90 minutes of moderate-tovigorous PA, 3 to 5 days per week, in which most of this time is devoted to aerobic and musclestrengthening activities (with a smaller amount of time spent on other forms of activity, such as
flexibility) (Moderate). When it was possible to determine the amount of time spent just on aerobic
activity, studies usually varied from 60 minutes per week to 150 minutes per week (Moderate).
Physical Activity Guidelines Advisory Committee Report E–14
Part E. Integration and Summary of the Science
Health Outcome: Functional Health (continued)
Falls:
Evidence exists for exercise programs that include 3 times per week of balance and moderateintensity strengthening activities at 30 minutes per session, with additional encouragement to
participate in moderate-intensity walking activities 2 or more times per week for 30 minutes a
session (Strong).
Evidence also exists for tai chi exercises (Moderate). It was difficult to ascertain an optimal PA
pattern for tai chi. Tai chi studies ranged from 1 hour per week to 3 hours or more per week
(Limited).
What is the evidence around accumulation?
No evidence is available.
What other unique comments should be made about the evidence of PA with this health
outcome?
Relative intensity is important to consider, as fitness levels are very low in many older adults.
It is important to increase exercise intensity and volume slowly to reduce adverse events,
especially injuries.
Health Outcome: Cancer
Types of studies?
Type 3a – extensive
What is the nature of the association of PA with Cancer?
There is a clear inverse association between PA and prevention of breast and colon cancer.
Strength of evidence: Strong
What is the effect size?
There is about a 30% lower risk for colon cancer and about a 20% lower risk for breast cancer.
Strength of evidence: Strong
Is there any evidence for an effect of sex, age, race/ethnicity?
This association exists for both men and women for colon cancer, as well as for adults of different
ages. There is reasonable evidence to show an association exists for different race/ethnic groups.
Strength of evidence: Sex = Strong, Age = Strong, Race/Ethnicity = Reasonable
Is there a dose-response effect?
There is a dose-response association between PA and the development of breast/colon cancer,
but the shape of the curve is unclear.
Strength of evidence: Reasonable
What is an effective PA dose regarding mode, duration, intensity, and frequency that is
supported by the evidence? (Strength of evidence in parentheses)
Data indicate at least 30 to 60 minutes per day of moderate-to-vigorous PA is needed to see
significantly lower risks (Reasonable). Data are primarily for aerobic LTPA (Strong).
Physical Activity Guidelines Advisory Committee Report E–15
Part E. Integration and Summary of the Science
Health Outcome: Cancer (continued)
What is the evidence on accumulation? (Strength of evidence in parentheses)
There is no information on accumulation of PA and cancer. However, the LTPA carried out by
subjects in observational studies likely is accumulated from different activities of various, but
unknown, duration (Limited).
What other unique comments should be made about the evidence of PA with this health
outcome? (Strength of evidence in parentheses)
There is a small body of Type 1 evidence for an association between improved quality of life and
fitness in breast cancer survivors (Strong).
There is growing evidence of a reduced risk of cancers of the endometrium and lung with
increased physical activity (Reasonable).
Health Outcome: Mental Health
Types of studies?
Type 1, 2a, 3a and 3b
What is the nature of the association of PA with Mental Health?
There is clear evidence that PA reduces risk of depression and cognitive decline in adults and
older adults. There is some evidence that PA improves sleep. There is limited evidence that PA
reduces distress/well-being and anxiety.
Strength of evidence: Depression and cognitive health = Strong; Sleep = Moderate; Distress/wellbeing and Anxiety = Limited
What is the effect size?
There is about a 20% to 30% lower risk for depression, distress/well-being, and dementia.
Strength of evidence: Strong
Is there any evidence for an effect of sex, age, race/ethnicity?
Risk reduction has been observed for men and women of all ages, but few studies have directly
compared results according to sex or age. Racial/ethnic minority groups have been
underrepresented in most studies, but limited results from prospective cohort studies suggest that
risk reduction among blacks and Hispanic/Latinos is similar to that among whites.
Strength of evidence: Limited
Is there a dose-response effect? (Strength of evidence in parentheses)
Reasonable evidence indicates a dose-response effect between PA and mental health. Moderate
and high levels of physical activity are similarly associated with lower risk of depression and
distress/well-being, compared to low levels of physical activity exposure, which is nonetheless
more protective than inactivity or very low levels of physical activity (Moderate). There is
insufficient evidence to determine whether there are dose-response relations with physical activity
for anxiety, cognitive health, and sleep (Limited).
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Part E. Integration and Summary of the Science
Health Outcome: Mental Health (continued)
What is an effective PA dose regarding mode, duration, intensity, and frequency that is
supported by the evidence?
Most evidence comes from PA programs of 3 to 5 days per week, 30 to 60 minutes per session
and moderate to vigorous intensity. Most evidence comes from aerobic and multi-modal
interventions (usually aerobic plus muscle strengthening activities). Only a few studies have
manipulated and compared features of physical activity and their effects on mental health. Aerobic
or resistance, and their combination, have positive effects. However, the minimal or optimal type or
amount of exercise for mental health is not yet known
Strength of evidence: Limited to Moderate
What is the evidence on accumulation?
Mental health outcomes have not differed when physical activity was continuous or intermittent in
nature, but studies have not directly compared single versus multiple sessions of similar amounts
of physical activity in controlled studies. Hence, there is insufficient evidence to determine whether
physical activity can be accumulated to achieve mental health benefits.
Strength of evidence: Limited
What other unique comments should be made about the evidence of PA with this health
outcome?
Positive findings from initial studies suggest that physical activity and exercise might reduce the
onset, progression, or adverse impact of central nervous system disorders other than dementia
that contribute to disability and mortality risk, such as multiple sclerosis and Parkinson’s disease.
Benefits of physical activity may also extend to other aspects of mental health that are important
contributors to overall quality of life, such as self-esteem and feelings of energy/fatigue. Sufficient
evidence exists to encourage more study in these areas, but presently not enough studies are
available to draw conclusions about how the effects of physical activity or exercise may differ
according to types of people or types and amounts of physical activity.
Health Outcome: Youth
Types of studies?
Physical Fitness:
Type 1, 2a, 2b, 3a, 3b: Cardiorespiratory
Type 2b: Muscular Strength
Body Mass and Composition:
Type 1, 2b, 3a, 3b
Cardiovascular and Metabolic Health:
Type 1, 2b, 3a, 3b
Bone Health:
Type 1, 3a
Mental Health:
Type 1, 2b, 3a, 3b: Depression
Type 1, 3b: Anxiety
Physical Activity Guidelines Advisory Committee Report E–17
Part E. Integration and Summary of the Science
Health Outcome: Youth (continued)
What is the nature of the association of PA with health for Youth? (Strength of evidence in
parentheses)
Physical Fitness:
There is a clear, positive association between PA and cardiorespiratory fitness and muscular
strength (Strong).
Body Composition:
There is a clear, positive association between PA and favorable body composition (Strong).
Cardiovascular and Metabolic Health:
There is a clear, positive association between PA and cardiovascular and metabolic health
(Strong).
Bone Health:
There is a clear, positive association between PA and bone health (Strong).
Mental Health:
There appears to be an association between PA and reduced symptoms of depression (Moderate),
anxiety (Weak), and higher self esteem (Limited).
Is there a dose-response effect?
Cardiovascular and Metabolic Health:
There appears to be a dose-response relationship; however, the precise pattern of this relationship
has not been determined.
Other Outcomes:
Either evidence is insufficient or the varying methodologies and insufficient numbers of intervention
trials preclude inferences about dose-response patterns for the remainder of the outcomes. Doseresponse studies are needed.
Is there any evidence for an effect of sex, age, race/ethnicity? (Strength of evidence in
parentheses)
Physical Fitness:
The association between PA and cardiorespiratory fitness and muscle strength exists for both boys
and girls, as well as in children and adolescents (Strong). The research is not adequate to draw
conclusions about race/ethnicity.
Body Composition:
The research is not adequate to draw conclusions about age, biological maturity, and race/ethnicity
for body mass and composition.
Cardiovascular and Metabolic Health:
Very little is known about the effects of sex, age, biological maturity, and race/ethnicity on the
relationship of PA to cardiovascular and metabolic health.
Physical Activity Guidelines Advisory Committee Report E–18
Part E. Integration and Summary of the Science
Health Outcome: Youth (continued)
Bone Health:
This association exists for both boys and girls, and is influenced by age and developmental status
(Strong). The window of opportunity appears to be in puberty and pre-menarchal years (Moderate).
The research is not adequate to draw conclusions about race/ethnicity.
Mental Health:
The research is not adequate to draw conclusions about sex, age, maturity, and race/ethnicity on
the relationship of PA to mental health.
What is an effective PA dose regarding mode, duration, intensity, and frequency that is
supported by the evidence?
Overall Conclusion:
Important health and fitness benefits can be expected by most children and youth who participate
daily in 60 or more minutes of moderate-to-vigorous physical activity (Strong).
Physical Fitness:
Vigorous aerobic activity 3 or more days per week significantly improves cardiorespiratory fitness.
Resistance training 2 or 3 days per week significantly improves muscular strength.
Body Composition:
Reductions in overall adiposity and visceral adiposity with exposure to regular moderate-tovigorous PA 3 to 5 days per week for 30 to 60 minutes have been observed.
Cardiovascular and Metabolic Health:
Vigorous aerobic activity 3 or more days per week significantly improves cardiovascular and
metabolic health.
Bone Health:
Targeted weight-loading activities that simultaneously influence muscular strength, done 3 or more
days per week, significantly improve bone mineral content and density.
What other unique comments should be made about the evidence of PA with this health
outcome?
Overall Conclusions:
It is important to minimize the potential risks of overtraining and injuries.
A wide-range of developmentally appropriate activities for children should be chosen.
Physical Activity Guidelines Advisory Committee Report E–19
Part E. Integration and Summary of the Science
Health Outcome: Understudied Populations
Types of studies?
Type 1, 2a, 2b
What is the nature of the association of PA with health for people with disabilities?
Consistency of evidence supports the use of PA to improve key health outcomes in people with
physical and cognitive disabilities.
Strength of evidence:
Physical Disability:
The strongest evidence is found under the categories of cardiorespiratory, musculoskeletal, and
mental health.
Cognitive Disability:
The strongest evidence is found under the categories of functional health and mental health.
What is the effect size? N/A
Level of evidence was based on number of significant trials reporting positive outcomes. Definition
of strength of evidence:
Strong: At least 75% of reviewed trials significant.
Moderate: 50% to 74% of reviewed trials significant.
Limited: Up to 49% of reviewed trials significant.
Strength of evidence:
Physical Disability:
Strong for cardiorespiratory health, musculoskeletal health, and mental health; Moderate for
functional health.
Cognitive Disability:
Strong for functional health and mental health; Moderate for cardiorespiratory health,
musculoskeletal health, and healthy weight and metabolic health.
Is there any evidence for an effect of sex, age, race/ethnicity?
No Is there a dose-response effect?
No direct data on dose response are available.
What is an effective PA dose regarding mode, duration, intensity, and frequency that is
supported by the evidence? (Strength of evidence in parentheses)
The majority of the studies included exercise doses typically used in studies with the general
population:
Intensity: 50% or more of heart rate reserve or VO2peak (Strong)
Frequency: 3 to 5 days per week (Strong)
Duration: 30 to 60 minutes (Strong)
Physical Activity Guidelines Advisory Committee Report E–20
Part E. Integration and Summary of the Science
Health Outcome: Understudied Populations (continued)
What is the evidence on accumulation?
No direct data are available on multiple bouts versus one long bout.
What other unique comments should be made about the evidence of PA for people with
disabilities?
PA is relatively safe and effective for people with disabilities and can improve several key health
outcomes. Very few serious adverse events have been reported (1.15% exercise versus 0.60% for
controls).
Health Outcome: Adverse Events
Types of studies?
Types: 1, 3a, 4
What is the nature of the association of PA with Adverse Events? (Strength of evidence in
parentheses)
The risk of musculoskeletal injuries is lower for non-contact (e.g., walking) and limited contact
(e.g., baseball) activities than for contact (e.g., basketball) and collision (e.g., football) activities
(Strong).
The usual dose of regular physical activity is directly related to the risk of musculoskeletal injury
(Strong) and inversely related to the risk of sudden adverse cardiac events (Strong).
The risk of musculoskeletal injuries and sudden cardiac adverse events is directly related to the
size of the difference between the usual dose of activity and the new or momentary dose of activity
(Strong).
The most consistently reported risk factor for musculoskeletal injuries (Strong) and sudden cardiac
adverse events (Strong) is inactivity and low fitness.
Is there any evidence for an effect of sex, age, race/ethnicity?
Older people are more susceptible to activity-related musculoskeletal injuries (Weak).
Females are more likely than males to suffer musculoskeletal injuries, but the difference a
be due to lower fitness (Weak).
Differences in the risk of musculoskeletal injuries among different race/ethnicity groups do
appear to be marked but have been infrequently studied (Weak).
ppears to
not
What is an effective PA dose regarding mode, duration, intensity, and frequency that is
supported by the evidence?
A series of small increases in activity each followed by a period of adaptation will cause fewer
adverse events than will larger or more frequent increases in activity (Weak).
The incidence of adverse events caused by moderate-intensity physical activity appears to be low
(Weak).
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Part E. Integration and Summary of the Science
Health Outcome: Adverse Events (continued)
What other unique comments should be made about the evidence of PA and Adverse
Events?
The benefits of regular physical activity far outweigh the risks of adverse events for outcomes that
encompass a broad spectrum of medical maladies such as all-cause mortality (Strong), functional
health (Moderate), and medical expenditures (Strong).
Appropriate clothing, gear, and equipment, as well as a safe environment, reduce the risk of
adverse events.
Integrating the Evidence: Questions and Answers
About the Health Benefits of Physical Activity
After it summarized the evidence linking physical activity to a variety of health outcomes
and populations, the PAGAC’s next step was to integrate this evidence in the following
questions and responses. Because the primary charge to the PAGAC was to review the
scientific evidence to inform the development of public health physical activity guidelines
and policy for Americans, the questions and answers primarily focus on major outcomes and
on issues involving dose response, particularly the minimum amount, intensity, duration,
and frequency associated with health benefits, as well as whether additional health benefits
are observed at higher levels of physical activity.
Overall Benefits of Physical Activity
Q-1. Does existing evidence indicate that people who are habitually physically active
have better health and a lower risk of developing a variety of chronic diseases than
do inactive people?
R-1. Yes. Very strong scientific evidence based on a wide range of well-conducted studies
shows that physically active people have higher levels of health-related fitness and a
lower risk profile for developing a number of disabling medical conditions than do
people who are inactive. In children and youth major benefits supported by strong
evidence include enhanced cardiorespiratory and muscular fitness, cardiovascular
and metabolic health biomarkers, bone health, body mass and composition. Less
strong evidence supports selected measures of mental health. In adults and older
adults strong evidence demonstrates that, compared to less active counterparts, more
active men and women have lower rates of all-cause mortality, coronary heart
disease, high blood pressure, stroke, type 2 diabetes, metabolic syndrome, colon
cancer, breast cancer, and depression. Strong evidence also supports the conclusion
that, compared to less active people, physically active adults and older adults exhibit
a higher level of cardiorespiratory and muscular fitness, have a healthier body mass
and composition, and a biomarker profile that is more favorable for the preventing
cardiovascular disease and type 2 diabetes and enhancing bone health. Modest
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evidence indicates that physically active adults and older adults have better quality
sleep and health-related quality of life. For older adults, strong evidence indicates
that being physically active is associated with higher levels of functional health, a
lower risk of falling, and better cognitive function.
Time course for benefits. Strong evidence indicates that increases in
cardiorespiratory and muscular fitness and improvements in various biomarkers that
appear in the causal pathways between increased activity and favorable clinical
outcomes and in some clinical outcomes, such as a decrease in depression, frequently
occur in weeks or a few months in response to a sustained increase in moderate- to
vigorous-intensity activity. The time course for a decrease in occurrence of various
chronic disease clinical outcomes has not been established but appears to require
longer exposure to an increased level of activity.
Q-2. What does the evidence indicate about dose of physical activity that is most likely to
provide many of the benefits indicated in R-1?
R-2. Current science, inter-individual differences in the biological responses to specific
activity regimens and the wide variety of benefits provided by being physically
active do not allow a single, highly precise answer to this question. However, as a
starting place for overall public health benefit, data from a large number of studies
evaluating a wide variety of benefits in diverse populations generally support 30 to
60 minutes per day of moderate- to vigorous-intensity physical activity on 5 or more
days of the week. For a number of benefits, such as lower risk for all-cause
mortality, coronary heart disease, stroke, hypertension, and type 2 diabetes in adults
and older adults, lower risk is consistently observed at 2.5 hours per week
(equivalent to 30 minutes per day, 5 days per week) of moderate- to vigorousintensity activity. The amount of moderate- to vigorous-intensity activity most
consistently associated with significantly lower rates of colon and breast cancer and
the prevention of unhealthy weight gain or significant weight loss by physical
activity alone is in the range of 3 to 5 hours per week.
By converting the intensity and duration of various aerobic activities into METminutes or MET-hours (intensity in METs x duration), it is possible to combine
activities of different types and intensities into a single measure of amount of
activity. For many studies, the amount of moderate- and vigorous-intensity activity
associated with significantly lower rates of disease or improvements in biomarkers
and fitness is in the range of 500 to 1,000 MET-minutes per week. An adult can
achieve a target of 500 MET-minutes per week by walking at about 3.0 miles per
hour for approximately 150 minutes per week (7.5 miles), walking faster at 4.0 miles
per hour for 100 minutes (6.6 miles) or jogging or running at 6 miles per hour for
about 50 minutes per week (5.0 miles). To achieve 1,000 MET-minutes per week,
these amounts of activity would need to be doubled. These MET-minutes per week
targets also can be achieved by performing various combinations of activities of
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different intensities and durations (See Table D.3 in Part D: Background and its
accompanying text for more details).
Very limited data are available on dose response in children and youth, but strong
evidence indicates that better fitness and health outcomes are observed when
60 minutes of moderate- to vigorous-intensities activity of various types is
accumulated throughout the day.
Q-3. Is there evidence that performing more than 30 minutes per day of moderate- to
vigorous-intensity activity on most days confers greater health benefits for some
health outcomes?
R-3. Yes. For a variety of health and fitness outcomes, including chronic disease
prevention, improvement of various disease biomarkers and the maintenance of a
healthy weight, reasonably strong evidence demonstrates that amounts of moderateto vigorous-intensity activity that exceed 150 minutes per week are associated with
greater health benefits. However, in a number of studies where such a dose response
is observed in preventing chronic disease or reducting all-cause mortality, the
relation appears to be curvilinear. This means that the absolute increase in benefits
becomes less and less for any given increase in the amount of physical activity. An
example of a curvilinear dose-response relation between the relative risk of all-cause
mortality and the amount of moderate-to-vigorous physical activity in hours per
week is displayed in Figure G1.3 (Part G. Section 1: All-Cause Mortality). As stated
in that chapter, “On average, compared to less than 0.5 hours per week of moderateto-vigorous physical activity, engaging in approximately 1.5 hours per week in such
activity is associated with about a 20% reduction in risk of all-cause mortality during
follow-up. Additional amounts of physical activity are associated with additional
reductions, but at smaller magnitudes, such that approximately 5.5 hours per week is
required to observe a further 20% reduction in risk (i.e., approximately 7.0 hours per
week is associated with approximately 40% reduction in risk compared with less
than 0.5 hours per week).” A somewhat similar curvilinear relation appears to exist
between amounts of moderate to vigorous activity and risk of coronary heart disease.
The added value of higher amounts of activity for helping maintain a healthy body
weight is discussed in the responses to Questions 15 to 17.
Q-4. For people who are physically inactive or unfit, does current science support the
concept that some activity is better than none?
R-4. PAGAC members spent substantial time considering this question and concluded
that for otherwise healthy sedentary individuals, some physical activity is better than
none. The least active in the population generally have the highest risk for various
negative health consequences and the most to gain from becoming more active.
Increasing evidence suggests that performing activity in amounts of no more than
about 1 hour per week at an intensity that is moderate relative to the person’s
capacity will provide small increases in cardiorespiratory and muscular fitness. In
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some studies, this amount of activity is associated with lower risk of all-cause
mortality and the incidence of coronary heart disease. At this lower amount and
intensity of activity, the benefits usually are less than that observed with greater
amounts of activity, and studies are much less consistent about the nature and
magnitude of these benefits. Nevertheless, the dose-response curves for the major
health benefits clearly indicate an inverse relation between the dose of activity and
rate of disease. Although the minimum amount of activity needed to produce a
benefit cannot be stated with certainty, nothing would suggest a threshold below
which there are no benefits. Therefore, for inactive adults any increase appears better
than none. To achieve benefits for various health outcomes equivalent to those
achieved by their more active peers, very inactive adults will need to progress
gradually to higher amounts and intensities of activity.
Q-5. If physical activity is performed at a vigorous intensity, are the health outcomes
greater than what has been observed with moderate-intensity activity?
R-5. Yes. For some favorable health and fitness outcomes strong evidence indicates that
an increase in intensity is associated with greater improvements compared to those
observed with moderate-intensity activity. For example, when a similar amount of
activity is performed per session, such as walking 3 miles per day, participants who
walk faster have a greater increase in cardiorespirtaory fitness than those who walk
more slowly. One problem in interpreting data that compares the benefits of
moderate versus vigorous activity in many observational and experimental studies is
that along with a difference in intensity between study groups, the amount or volume
of activity performed also differs. For example, if participants in two groups are
physically active 30 minutes per day 5 days per week, but one group walks at 3 miles
per hour and the other jogs at 6 miles per hour, both the intensity and the amount of
activity performed will be different between the two groups. In this case it is not
possible to tell for sure whether differences in health or fitness outcomes between the
2 groups are due to the difference in the intensity or the amount of activity
performed, or both. It is important to recognize that the rate of energy expenditure
goes up quite rapidly with increases in intensity for some types of activity, such as
going from walking to jogging or running.
As people consider increasing their physical activity to high doses of vigorousintensity activity with the primary goal of achieving favorable health outcomes, they
need to be aware that such increases may accelerate the injury rate disproportionate
to the benefits accrued. This appears to be especially true for people who have been
inactive for extended periods and who then rapidly increase the amount and/or
intensity of activity they perform.
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Q-6. Is there evidence that the frequency of physical activity sessions influences health
and fitness outcomes independent of the amount of activity performed?
R-6. Very limited published research has systematically evaluated health or fitness
benefits in response to different frequencies of activity sessions per week when the
amount of activity is held reasonably constant. In experimental studies, comparisons
have been made between 2 versus 3 or more sessions per week for both aerobic and
resistance activity, but the amount of activity performed increased as the number of
sessions increased so it is not possible to separate out the effects of increasing the
session frequency from the effects of increasing the amount. Most of the data from
prospective cohort studies with outcomes of all-cause mortality or chronic disease
morbidity and mortality do not provide information about frequency of activity
independent of intensity and amount, but the very limited data available indicate that
when activity amount is controlled for, the effect of session frequency is not
significant.
When many adults with sedentary occupations reach the range of 500 to 1,000 METminutes per week of leisure-time physical activity (LTPA), it is very likely that this
activity is the result of multiple sessions performed during the week. Experimental
studies that show significant improvements in health-related outcomes typically
feature session frequencies ranging between 3 and 5 times per week. Also, as the
response to the Question 7 demonstrates, a growing, but still limited, body of
evidence indicates that multiple short bouts (10 or more minutes) per day of aerobic
activity produces improvements in cardiorespiratory fitness and selected
cardiovascular disease (CVD) biomarkers similar to that obtained with a single bout
of equal total duration and intensity.
Overall, one interpretation of the existing data is that for health and fitness benefits,
the frequency of activity is much less important than the amount or intensity. Many
experimental studies since 1995 have demonstrated beneficial effects of 120 to 150
minutes per week of moderate- or vigorous-intensity activity usually performed
during 3 to 5 sessions per week, so we know that this frequency of activity is
effective. Only limited data are available comparing the benefits from just one or two
sessions per week with multiple sessions spread throughout the week with activity
amount and intensity held constant. Again, while very limited data are available from
direct comparisons, the rate of certain types of adverse events (e.g., joint irritation,
muscle soreness) may be lower when performing a similar amount and intensity of
activity but during more sessions per week.
Q-7. Is there evidence that physical activity can be accumulated throughout the day for
some health and fitness outcomes?
R-7. The concept of accumulation refers to performing multiple short bouts of physical
activity throughout the day. Some scientific evidence of moderate strength suggests
that accumulating 30 or more minutes per day of moderate- to vigorous-intensity
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aerobic activity throughout the day in bouts of 10 minutes or longer produces
improvements in cardiorespiratory fitness. Limited data indicate that accumulated
short bouts improve selected CVD biomarkers in a manner generally similar to that
observed when activity of a similar amount and intensity is performed in a single
bout of 30 or more minutes. These experimental studies have primarily evaluated the
effects of multiple short bouts of 8 to 10 minutes duration versus longer bouts of
30 to 40 minutes and have not provided data on numerous shorter bouts (e.g.,
30 1-minute bouts per day). Data on the effects of accumulating activity involving
multiple short bouts for the prevention of major clinical outcomes, such as all-cause
mortality, CVD, diabetes, and selected cancers, are very limited because of the type
of data collected from questionnaires used in most prospective observational studies.
Using data from these questionnaires, it has not been possible to precisely
differentiate between activities conducted in a single, long bout versus those
conducted in multiple, short bouts over the day. Prospective cohort studies with
clinical outcomes have tended to present their data according to categories of the
total amount of activity performed, and this total amount is likely to be accumulated
from different activities of varying, but unknown durations and frequencies, over the
course of the day.
Q-8. Is there evidence that performing bouts of walking as a frequent routine is associated
with positive health effects?
R-8. Yes. Strong evidence shows that a regimen of brisk walking provides a number of
health and fitness benefits for adults and older adults. For example, women in the
United States who walk 2 to 3 hours per week have a significantly lower risk of allcause mortality and cardiovascular disease than do women who report no or very
little walking. Also, for people walking for equivalent amounts of time, a faster pace
is associated with a lower risk of cardiovascular disease, type 2 diabetes, and allcause mortality. Strong evidence also shows that frequent bouts of walking increase
cardiorespiratory fitness, especially in people who have been performing little
activity on a regular basis. Limited to moderate evidence suggests that walking helps
to maintain bone density and reduce fractures over time, especially in women, and
helps to maintain joint health and functional ability in adults and older adults.
Q-9. What does the scientific evidence indicate about the pattern of physical activity that
is most likely to produce the fewest adverse medical events while providing health
benefits?
R-9. Much of the research that addresses this question has evaluated the risk of
musculoskeletal injuries or sudden cardiac death during vigorous physical activity
(e.g., jogging, running, competitive sports, military training) with few wellconducted studies evaluating the risk during moderate-intensity activity intended
primarily to improve health. Activities with fewer and less forceful contact with
other people or objects have appreciably lower injury rates than do collision or
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contact sports. Walking for exercise, gardening or yard work, bicycling or exercise
cycling, dancing, swimming, and golf, which are already popular in the United
States, are activities with the lowest injury rates. Risk of musculoskeletal injury
during activity increases with the total volume of activity (e.g., MET-hours per
week). Intensity, frequency, and duration of activity all contribute to the risk of
musculoskeletal injuries but their relative contributions are unknown. For sudden
cardiac adverse events, intensity appears to be more important than frequency or
duration. The limited data that do exist for medical risks during moderate-intensity
activity indicate that the risks are very low for activities like walking and that the
health benefits from such activity outweigh the risk.
Q-10. What does the scientific evidence say about actions that can be taken to reduce the
risk of injury during physical activity?
R-10. Research with a variety of populations and methods indicates that injuries are more
likely when people are more physically active than usual. The key point to
remember, however, is that when individuals do more activity than usual, the risk of
injury is related to the size of the increase. A series of small increments in physical
activity each followed by a period of adaptation is associated with lower rates of
musculoskeletal injuries than is an abrupt increase to the same final level. Although
the safest method of increasing one’s physical activity has not been empirically
established, adding a small and comfortable amount of light to moderate-intensity
activity such as walking, 5 to 15 minutes per session, 2 to 3 times per week, has a
low risk of musculoskeletal injury and no known risk of sudden severe cardiac
events.
For people with stable activity habits, risk of injury is directly related to the total
volume of activity performed. Other things being equal, people who are very
physically active are more likely to incur an activity-related injury than people who
are active to a lesser degree. Some evidence suggests, however, that even though
more active people are more likely to incur a physical activity-related injury they
may suffer fewer overall injuries because they are less likely to be injured in other
settings such as at work or around the home.
Q-11. Is there evidence regarding who should see a physician or have a medical
examination before increasing the amount or intensity of physical activity they
perform?
R-11. The protective value of a medical consultation for persons with or without chronic
diseases who are interested in increasing their physical activity level is not
established. No evidence is available to indicate that people who consult with their
medical provider receive more benefits and suffer fewer adverse events than people
who do not. Also unknown is the extent to which official recommendations to seek
medical advice before augmenting one’s regular physical activity practices may
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reduce participation in regular moderate physical activity by implying that being
active may be less safe and provide fewer benefits than being inactive.
Q-12. What are the major health benefits provided by an increase in aerobic (endurance)
activity?
R-12. Aerobic activity of moderate to vigorous intensity performed on a regular basis
results in improvements in cardiorespiratory fitness (VO2max) with an increase in
the capacity and efficiency of the cardiorespiratory system to transport oxygen
to skeletal muscles and for muscles to use this oxygen. This increase in
cardiorespiratory fitness has a strong inverse association with risk of all-cause
mortality and a variety of chronic diseases. The evidence is strong that aerobic
activity has favorable effects on various biomarkers for CVD and type 2 diabetes
(e.g., atherogenic lipoprotein profile, blood pressure, insulin sensitivity) in adults and
older adults with and without these diseases. Much of the physical activity associated
with lower risk for all-cause mortality, coronary heart disease, stroke, hypertension,
breast and colon cancer, and depression in many of the prospective observational
studies published since 1995 has been moderate- to vigorous-intensity aerobic
activity. For most people, performing aerobic activity that requires the rhythmic use
of large muscles and the movement of the body mass against gravity (e.g., walking,
jogging, cycling, climbing stairs, dancing) is the most effective way to increase the
rate of energy expenditure and better achieve energy balance. For many of the
benefits linked to preventing various chronic diseases, aerobic activity performed at
moderate to vigorous intensity in the range of 500 to 1,000 MET-minutes per week is
associated with a significantly lower risk.
Q-13. What are the major health benefits provided by resistance or muscle-strengthening
activity?
R-13. Strong evidence exists in youth, adults and older adults that muscle-strengthening
exercises that load skeletal muscle and bone increase muscle mass, strength, and
quality and increase bone mineral density. Evidence is moderate that musclestrengthening exercises improve functional ability in older adults and lead to
improvements in muscle strength, joint pain, stiffness, and functional ability in adults
with osteoarthritis. In combination with balance training, muscle-strengthening
exercises reduce risk of falls in older adults at risk for falls (this evidence is
discussed in more detail in Question 22). Resistance exercise can help maintain lean
body mass during a program of weight loss, but by itself results in little weight loss.
Most of the evidence supports a resistance activity program with the following
characteristics: progressive muscle strengthening exercises that target all major
muscle groups performed on 2 or more days per week. To enhance muscle strength,
8 to 12 repetitions of each exercise should be performed to volitional fatigue. One set
is effective; however, limited evidence suggests that 2 or 3 sets may be more
effective.
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Q-14. What is the evidence that flexibility activities provide health benefits?
R-14. Flexibility is an important element of overall fitness. However, the evidence that
flexibility exercises by themselves confer health benefits is very limited. Most
well-designed exercise interventions in youth, adults, and older adults include a brief
flexibility routine as part of the intervention and often as the control condition, thus
preventing the assessment of the relative benefits of flexibility training alone. Some
evidence indicates that balanced exercise interventions that include flexibility
activities reduce the risk of injuries.
Energy Balance
Q-15. What is the amount of physical activity that is necessary for weight stability over the
long term?
R-15. The optimal amount of physical activity needed for weight maintenance (defined as
less than 3% change in weight) over the long-term is unclear. However, the evidence
is clear that physical activity provides benefit for weight stability. A great deal of
inter-individual variability exists with physical activity and weight stability, and
many persons may need more than 150 minutes of moderate-intensity activity per
week to maintain weight. Data from recent well-designed randomized controlled
trials lasting up to 12 months indicate that aerobic physical activity performed to
achieve a volume of 13 to 26 MET-hours per week is associated with approximately
a 1% to 3% weight loss (i.e., an amount generally considered to represent weight
stability). Thirteen MET-hours per week is approximately equivalent to walking at
4 miles per hour for 150 minutes per week or jogging at 6 miles per hour for
75 minutes per week.
Q-16. What is the evidence for the amount of physical activity that is necessary for weight
loss in adults?
R-16. A wide range of studies provides evidence of a dose-response relation between
physical activity and weight loss. Clear, consistent data show that a large volume of
physical activity is needed for weight loss in the absence of concurrent dietary
changes. The physical activity equivalent of 26 kilocalories per kilogram of body
weight (1,560 MET-minutes) or more per week is needed for weight loss of 5% or
greater. Smaller amounts of weight loss are seen with smaller amounts of physical
activity (as noted in R-15). This relatively high volume of physical activity is
equivalent to walking about 45 minutes per day at 4 miles per hour or about
70 minutes per day at 3 miles per hour, or jogging 22 minutes per day at 6 miles
per hour.
The role of energy intake (diet) must be considered in any discussion of weight
control. When calorie intake is carefully controlled at a baseline level, the magnitude
of any weight loss is what would be expected given the increase in energy
Physical Activity Guidelines Advisory Committee Report E–30
Part E. Integration and Summary of the Science
expenditure of the person’s physical activity. However, in situations in which
people’s dietary intake is not controlled, the amount of weight loss due to the
increase in physical activity is not commensurate to what would be expected.
Therefore, for most people to achieve substantial weight loss (i.e., more than 5%
decrease in body weight), a dietary intervention also is needed. The dietary
intervention could include either maintenance of baseline caloric intake, or a
reduction in caloric intake to accompany the physical activity intervention. The
magnitude of change in weight due to physical activity is additive to that associated
with caloric restriction.
Q-17. Is there evidence that physical activity provides benefit for weight maintenance in
adults who have previously lost substantial body weight?
R-17. The scientific evidence for the effectiveness of physical activity alone in preventing
weight regain following significant weight loss is limited. Available data indicate
that to prevent substantial weight regain over 6 months or longer, many adults need
to exercise in the range of 60 minutes of walking or 30 minutes of jogging daily
(approximately 4.4 kilocalories per kilogram per day of activity energy expenditure).
The literature generally supports the concept that “more is better” for long-term
weight maintenance following weight loss. Further, the evidence indicates that
individuals who are successful at long-term weight maintenance appear to limit
caloric intake in addition to maintaining physical activity.
Q-18. For people who are overweight or obese is there evidence that physical activity
provides health benefits irrespective of assisting with energy balance?
R-18. Yes. Strong evidence shows that physically active adults who are overweight or
obese experience a variety of health benefits that are generally similar to those
observed in people of optimal body weight (BMI = 18.5-24.9). These benefits
include lower rates of all-cause mortality, coronary heart disease, hypertension,
stroke, type 2 diabetes, colon cancer, and breast cancer. At least some of these
benefits appear to be independent of a loss in body weight, while in some cases
weight loss in conjunction with an increase in physical activity results in even greater
benefits. Because of the health benefits of physical activity that are independent of
body weight classification, adults of all sizes and shapes gain health and fitness
benefits by being habitually physically active.
Youth
Q-19. What does the evidence indicate about the major physical fitness and health benefits
of physical activity in children and youth?
R-19. Strong evidence demonstrates that the physical fitness and health status of children
and youth is substantially enhanced by frequent physical activity. Compared to
inactive young people, physically active children and youth have higher levels of
Physical Activity Guidelines Advisory Committee Report E–31
Part E. Integration and Summary of the Science
cardiorespiratory endurance and muscular strength and well documented health
benefits include lower body fatness, more favorable cardiovascular and metabolic
disease risk profiles, enhanced bone health, and reduced symptoms of anxiety and
depression. These conclusions are based on the results of observational studies in
which higher levels of physical activity were found to be associated with favorable
health parameters as well as experimental studies in which exercise treatments
caused improvements in physical fitness and various health-related factors.
Q-20. What does the evidence indicate about the dose of physical activity that is most likely
to provide health benefits for children and youth?
R-20. Few studies have provided data on the dose response for various health and fitness
outcomes in children and youth. However, substantial data indicate that important
health and fitness benefits can be expected to accrue to most children and youth who
participate daily in 60 or more minutes of moderate to vigorous physical activity.
Also, the Committee concluded that certain specific types of physical activity should
be included in an overall physical activity pattern in order for children and youth to
gain comprehensive health benefits. These include regular participation in each of
the following types of physical activity on 3 or more days per week: resistance
exercise to enhance muscular strength in the large muscle groups of the trunk and
limbs, vigorous aerobic exercise to improve cardiorespiratory fitness and
cardiovascular and metabolic disease risk factors, and weight-loading activities to
promote bone health.
Older Adults
Q-21. Is there evidence that the target dose for physical activity should differ for older
adults?
R-21. Yes. If a person has a low exercise capacity (physical fitness), the intensity and
amount of activity needed to achieve many health-related and fitness benefits is less
than for someone who has a higher level of activity and fitness. For example, relative
improvements in cardiorespiratory endurance and muscle strength produced by an
increase in physical activity are more closely associated with the activity intensity
relative to the capacity of the individual (e.g., percent of VO2max or one repetition
max [1RM]) than to the absolute intensity of the activity (e.g., 6 miles per hour or
100 pounds). Because the exercise capacity of adults tends to decrease as they age,
older adults generally have lower exercise capacities than younger persons. Thus,
they need a physical activity plan that is of lower absolute intensity and amount (but
similar in relative intensity and amount) than is appropriate for more fit people,
especially when they have been sedentary and are starting an activity program.
Physical Activity Guidelines Advisory Committee Report E–32
Part E. Integration and Summary of the Science
Q-22. What is the evidence that physical activity in older adults can reduce or prevent
falls?
R-22. For older adults at risk of falling, strong evidence exists that regular physical activity
is safe and reduces falls by about 30%. Most evidence supports a program of
exercise with the following characteristics: 3 times per week of balance training and
moderate-intensity muscle-strengthening activities for 30 minutes per session and
with additional encouragement to participate in moderate-intensity walking activities
2 or more times per week for 30 minutes per session. Some evidence, albeit less
consistent, suggests that tai chi exercises also reduces falls. Successful reduction in
falls by tai chi interventions resulted from programs conducted from 1 to 3 hours or
more per week. No evidence indicates that planned physical activity reduces falls in
adults and older adults who are not at risk for falls.
Understudied Populations
Q-23. Is there evidence that physical activity provides health benefits to persons with
various disabilities?
R-23. Yes. However, for many physical and cognitive disabilities, scientific evidence for
various health and fitness outcomes is still limited due to the lack of research. The
goal of the scientific review in persons with disabilities was not to consider exercise
as a therapy for disability but to evaluate the evidence that physical activity provides
the general health and fitness benefits frequently reported in populations without
these disabilities (e.g., improvements in physical fitness, biomarkers for chronic
disease, physical independence, health-related quality of life). Moderate to strong
evidence indicates that increases in aerobic exercise improve cardiorespiratory
fitness in individuals with lower limb loss, multiple sclerosis, stroke, spinal cord
injury, and mental illness. Limited data show similar results for people with cerebral
palsy, muscular dystrophy, and Alzheimer’s disease. Moderate to strong evidence
also exists for improvements in walking speed and walking distance in patients with
stroke, multiple sclerosis, and intellectual disabilities. Quite strong evidence
indicates that resistance exercise training improves muscular strength in persons with
such conditions as stroke, multiple sclerosis, cerebral palsy, spinal cord injury, and
intellectual disability. Although evidence of benefit is suggestive for such outcomes
as flexibility, atherogenic lipids, bone mineral density, and quality of life, the data
are still very limited.
For a majority of the studies reviewed involving persons with disabilities, the
exercise regimen followed was that currently recommended for the general public —
aerobic exercise of 30 to 60 minutes, 3 to 5 days per week at moderate intensity, and
resistance training with 1 or 2 sets of 8 to 12 repetitions using appropriate muscle
groups 2 to 3 times per week (intensity adjusted for the individual’s capacity). Data
comparing various doses of exercise in a single study are not available. In the studies
Physical Activity Guidelines Advisory Committee Report E–33
Part E. Integration and Summary of the Science
reviewed, participants had to meet study eligibility and, in some cases, had to have a
pre-participation medical evaluation, but the medical adverse event rate was low and
did not differ between exercise program participants and non-exercise controls.
Q-24. Is there evidence regarding the health benefits as well as risks of physical activity for
women during pregnancy and the postpartum period?
R-24. Substantial data from observational studies indicates that moderate-intensity physical
activity by generally healthy women during pregnancy increases cardiorespiratory
fitness without increasing the risk of low birth weight, preterm delivery, or early
pregnancy loss. The results of several studies also indicate that moderate-intensity
physical activity does not increase the risk of preeclampsia. Available data from
recent observational studies show a favorable association between moderateintensity activity during early pregnancy and somewhat lower rates of preeclampsia
and gestational diabetes mellitus (GDM), although these data are not yet conclusive.
For moderate-intensity activity during pregnancy, the scientific evidence is strong
that the risks are very low, but the science is less strong in documenting improved
health outcomes for the mother or child. The few studies that have been conducted
on the risks and benefits of vigorous activity by women who are pregnant provide
very limited data that this level of activity is associated with small reductions in birth
weight compared to birth weights of infants born to less active women.
Moderate-intensity physical activity during the postpartum period does not appear to
adversely affect milk volume or composition or infant growth, and moderately strong
evidence suggests that it results in enhanced cardiorespiratory fitness and mood of
the mother. Physical activity alone does not produce weight loss except when
combined with dietary changes.
Dose-response studies of physical activity and health outcomes for moderate- or
vigorous-intensity physical activity during pregnancy or the postpartum period have
not been conducted. Most studies evaluating possible benefits have promoted
moderate-intensity activity for 120 to 150 minutes per week.
Q-25. Is there evidence that the physical activity dose for improving health and fitness
should differ for people depending upon race or ethnicity?
R-25. Since 1995, only a limited number of prospective studies investigating the relation
between physical activity and health outcomes have had adequate samples of
non-Hispanic white men or women and one or more other race/ethnicities, which
would allow a direct comparison of benefits. In the observational cohort studies with
all-cause mortality or cause-specific chronic disease morbidity and mortality as the
outcome and with sufficient samples sizes and event rates to have reasonable power
to detect meaningful difference between race and ethnic groups, no differences have
been reported. In prospective observational studies conducted in countries where the
majority of the population is other than non-Hispanic white, the generally favorable
Physical Activity Guidelines Advisory Committee Report E–34
Part E. Integration and Summary of the Science
Physical Activity Guidelines Advisory Committee Report E–35
relation between higher levels of physical activity and chronic disease events is
similar to many of the studies reporting on non-Hispanic white populations. In the
few experimental studies where aerobic exercise training was the intervention, no
meaningful differences have been reported for changes in cardiorespiratory fitness,
body weight, or cardiovascular disease biomarkers when comparing non-Hispanic
white and African-American men and women. Thus, based on the currently available
scientific evidence, the dose of physical activity that provides various favorable
health and fitness outcomes appears to be similar for adults of various races and
ethnicities.
Reference List
1. American College of Cardiology, American Heart Association. Methodology manual
for ACC/AHA guideline writing committees 2008 [cited 6 A.D. May 23] Available
from http://www.americanheart.org/presenter.jhtml?identifier=3039684.
Part F:
Scientific Literature Search
Methodology
Background
Immediately after HHS Secretary Michael Leavitt announced plans for the development of
federal physical activity guidelines on October 27, 2006, the Centers for Disease Control
and Prevention (CDC) was assigned to support the Physical Activity Guidelines Advisory
Committee’s (PAGAC) review of the scientific literature. Working with an advisory
committee, staff of the Division of Nutrition, Physical Activity and Obesity (DNPAO) at
CDC’s National Center for Chronic Disease Prevention and Health Promotion developed a
conceptual framework for the literature search. They also established a process to
systematically abstract published articles and to make these abstracts readily accessible to
PAGAC members and consultants. The product of this effort is called the Physical
Activity Guidelines for Americans Scientific Database (http://apps.nccd.cdc.gov/
PhysicalActivityGuidelines).
Conceptual Framework
The overall conceptual framework for this project is found in Figure F.1. The scientific
literature review for Physical Activity Guidelines for Americans was initially organized
around 8 health outcome domains of interest: Cardiorespiratory Health, Metabolic Health,
Mental Health, Musculoskeletal Health, Functional Health, Cancer, All-Cause Mortality,
and Adverse Events. Of particular interest was the relevant scientific literature that relates
7 characteristics of physical activity (or exposures) to these health outcomes: intensity,
frequency, duration, pattern, type, caloric expenditure, and volume. Also of interest — as
related to these physical activity “exposures” — are physiologic states and adaptations to
physical activity that may be precursors to the health outcomes listed above.
Research Questions
At least 7 key research questions were used to guide the literature review and the
deliberations of the PAGAC. For each health outcome of interest:
1. Is there sufficient evidence that physical activity is associated with [Outcome]?
2. Is there sufficient evidence to support differing intensities of physical activity in
relation to the association with [Outcome] or precursors?
Physical Activity Guidelines Advisory Committee Report F–1
Part F: Scientific Literature Search Methodology
Figure F.1. Physical Activity Guidelines for Americans: Conceptual Framework for Literature Review
All arrows will be examined for heterogeneity across demographic characteristics (e.g., sex, age, race/ethnicity). Evidence will also be
examined for select special population groups.
CHD, coronary heart disease; PAD, peripheral arterial disease
• Insulin
Resistance
• Insulin
Sensitivity
• Glucose
Uptake
• Metabolic
Syndrome
• Overweight
• Constipation
• Fitness
• Hormonal
Influences
• Sleep Quality
Intensity
Frequency
Duration
Pattern
Caloric Expenditure
Type
Metabolic
Health
(Including
Diabetes and
Obesity)
Adverse Events and Risks of Physical Activity
Functional
Health
Health Outcomes
Risk Factors
Cardiorespiratory
Health
(Including
CHD, PAD,
Stroke)
• Dyslipidemias
• Blood Pressure
• Hemostatic/
Coagulation
Factors
• Asthma
• Fitness
• Cardiac
Function
• Lung Function
Mental
Health
• Anxiety
• Depression
• Self-Concept
• Sleep Quality
• Cognitive
Function
Musculoskeletal
Health
(Including
Osteoporosis)
• Bone
Mineralization
• Flexibility
• Strength
• Balance
• Maturation/
Growth
• Fitness
• Motor Skill
Development
• Muscle Fiber
• Quality of Life
• Functional
Independence
• Balance
• Pain
• Fall Prevention
Cancer
• Bowel Transit
Time
• Hormonal
Factors
• Immune
Function
• Linkages With
Other
Behaviors
AllCause
Mortality
Physical Activity Exposure
• Strength
• Balance
• Fitness
• Previous
Injury
• Family History
Physical Activity Guidelines Advisory Committee Report F–2
Part F: Scientific Literature Search Methodology
3. Is there sufficient evidence that the accumulation of multiple short periods of
physical activity is associated with [Outcome] or precursors?
4. Is there sufficient evidence of increased risk with physical activity associated with
[Outcome]?
5. Is there sufficient evidence that supports a pattern of weekly regularity (days per
week) of physical activity and association with [Outcome] or precursors?
6. Is there sufficient evidence that different modes (types) of physical activity are
(differentially and similarly) associated with [Outcome]?
7. Is there sufficient evidence that a physical activity exposure other than 30 minutes
per day on most, preferably all, days each week is associated with [Outcome]?
Operational Plan
Following from the conceptual framework, 3 CDC teams were formed to conduct the
literature reviews around 3 key life stages: youth (aged 5 to 19 years), adults (aged 19 to 64
years), and older adults (aged 65 years and older). All aspects of the literature review
(i.e., search strategy development and execution, review and triage of papers, cataloguing,
retrieving, coding, data entry, quality control, and payment of coders) were managed by the
teams. Two scientists (one senior, one junior) were appointed as co-leads for each life-stage
team, and coders were assigned to the teams based on the review workload (e.g., more
studies were available for adults than for youth). In addition, a separate team was formed to
develop and implement quality control procedures.
Phase 1 of the literature review process (October 2006 through June 2007) was carried out
by conducting systematic searches of the scientific literature on physical activity and the
health outcomes described above. During this phase, the teams held weekly meetings to
discuss issues that members were encountering and to devise solutions to move the project
forward. Issues included literature search terms, inclusion/exclusion criteria for the literature
search, study quality assessment, abstraction form and quality control, database/systems
issues, abstraction progress, qualifications required of the coders, certification process and
selection of coders, training sessions/agenda for abstractors, certificates developed and sent
to certified abstractors, retraining issues, termination of abstractors due to production or
quality control problems, development of an operations manual, preparation for the PAGAC
meetings and materials, health outcome tables, timelines, team reviews, database revisions,
subcommittee reviews/updates, and payment of the coders and scientific advisors.
Phase 2 of the literature review process (July 2007 through March 2008) began after the first
PAGAC meeting June 28-29, 2007, and was guided by the needs of the PAGAC. During
this phase, team members updated the Phase 1 literature review through June 2007 and
worked with PAGAC members to obtain scientific papers that were not abstracted during
Physical Activity Guidelines Advisory Committee Report F–3
Part F: Scientific Literature Search Methodology
Phase 1. This process is described in Appendix F.1. (Appendix F.1 can be accessed at
http://www.health.gov/paguidelines/report/.
Literature Review
Working from the literature review conceptual framework, the CDC teams performed a
standardized review of the scientific literature to provide evidence for the deliberations of
the PAGAC.
Searching the MEDLINE Database
The first step of the review process was to gather studies for possible inclusion in the
database, using defined search strategies (Appendix F.2, which can be accessed at
http://www.health.gov/paguidelines/report/). Search terms were selected for physical
activity and for each identified health outcome: cardiovascular and respiratory health,
metabolic health, musculoskeletal health, cancer, functional health, mental health, all-cause
mortality, and injuries/adverse events.
Using the Ovid interface, the CDC teams searched the National Library of Medicine’s
(NLM) MEDLINE Database using only Medical Subject Headings (MeSH) major
descriptors for the physical activity term set. They used a combination of MeSH descriptors
and text word synonyms to search for the health outcome terms set. A listing of all MeSH
headings used in the search strategies is included in Appendix F.2.
Three searches were run, and a combination of MeSH headings and text word synonyms
were used to limit retrieval to 3 age groups: youth, adults, and older adults. To capture any
articles not indexed by age, a fourth search was run, excluding all previous age group
retrieval. A fifth search was run, combining all age groups to capture items indexed to
multiple age groups. The search strategies for the 5 groups are included in Appendix F.2.
Each search was further limited by restricting retrieval to English language and to articles
published after 1994 that dealt with human subjects and contained abstracts. Finally, the
searches excluded 3 publication types — comments, editorials, and reviews. Search results
were stored in Word files and imported into Reference Manager Database files.
Selecting the Articles
The CDC teams developed specific inclusion and exclusion criteria to determine whether
studies would be eligible for abstraction. They also developed an inclusion/exclusion coding
system that allowed them to classify references efficiently and accurately for the abstraction
process. This process was divided into 2 phases: Certain studies of physical activity and a
diagnosable health outcome were abstracted during Phase 1; other studies of physical
activity and risk factors for the health outcomes were held for possible abstraction at a later
date (Phase 2), if requested by the PAGAC.
Physical Activity Guidelines Advisory Committee Report F–4
Part F: Scientific Literature Search Methodology
Physical Activity Guidelines Advisory Committee Report F–5
Inclusion and Exclusion Criteria
Articles were considered for inclusion in the review if they met certain criteria. Similarly,
articles with certain criteria were excluded from the review. Appendix F.3 provides a
detailed explanation of the inclusion and exclusion criteria developed for this review.
(Appendix F3 can be accessed at http://www.health.gov/paguidelines/report/.)
Abstracting the Articles
For each scientific article, abstractors recorded the following information: Overall study
design; sample and participant characteristics; intervention design and duration (if an
intervention study); physical activity exposure(s), including the dose of physical activity
provided to participants or in which they participated; follow-up time period; health
outcome(s); and the most advanced study results. For example, if a study presented an
analysis adjusted for age and presented the same analysis adjusted for age and body mass
index (BMI), the abstractor was instructed to record the age- and BMI-adjusted results.
Abstractors were hired, trained, and certified to perform all abstracting duties, and strict
quality control procedures were used throughout the abstraction project. The quality control
team checked and corrected 12.5% of abstracted papers. Abstractors were put on
probationary status if they did not meet quality control standards. Cursory checks of
abstractions were conducted, and subsequent corrections were made by all members of the
Physical Activity Guidelines team at CDC.
A Web-based data entry system was developed to manage all abstracted studies for this
project. This system was modeled after a similar system that CDC has used to abstract
studies for the Guide to Community Preventive Services, which provides systematic reviews
of community-based interventions. The physical activity Web-based data entry system
includes summary tables of the scientific articles abstracted as part of the literature review
for the Physical Activity Guidelines for Americans. The summary tables can be accessed at
http://apps.nccd.cdc.gov/PhysicalActivityGuidelines.
Part G. Section 1:
All-Cause Mortality
Introduction
This chapter examines the relation between physical activity and all-cause mortality. Two
leading causes of mortality, both in the United States as well as globally, are cardiovascular
disease and cancer, with both diseases estimated to be responsible for 43% of all deaths
globally (1). From a biological perspective, the evidence is strongly persuasive that physical
activity reduces the occurrence of these leading causes of death (discussed in the individual
chapters on these diseases); thus, it is also biologically plausible for physical activity to
postpone the occurrence of all-cause mortality. (Because we all die eventually, when the
phrase “lower risk of all-cause mortality” is used in this chapter, it refers to lower risk
during the period of follow-up in a study; i.e., postponed mortality.)
Review of the Science
Overview of Questions Addressed
This chapter addresses 5 specific questions:
1. Is there an association between physical activity and all-cause mortality? If so, what
is the magnitude of this association?
2. What is the minimum amount of physical activity associated with significantly lower
risk of all-cause mortality?
3. Is there a dose-response relation between physical activity and all-cause mortality?
4. What is the shape of the dose-response relation between physical activity and
all-cause mortality?
5. Is the relation between physical activity and all-cause mortality independent of
adiposity?
Data Sources and Process Used to Answer Questions
To provide evidence-based answers to the above questions, the All-cause Mortality
subcommittee obtained data from a search of the Physical Activity Guidelines for Americans
Scientific Database (see Part F: Scientific Literature Search Methodology, for a full
description of the database). The Database contains studies published in 1995 and later. The
Physical Activity Guidelines Advisory Committee Report G1–1
Part G. Section 1: All-Cause Mortality
selection criteria were broad and included searching for studies of all age groups, all study
designs, and all physical activity types that had the outcome of all-cause mortality. This
retrieved 83 publications, of which 7 were excluded for the following reasons: 3 studies of
exercise-related mortality were covered in another chapter; 2 studies of survival among
cancer patients were covered in another chapter; 1 study provided essentially duplicate
results on physical activity and all-cause mortality as another; and 1 study did not provide
results on the specific association of physical activity with all-cause mortality. An additional
3 studies of cardiovascular or muscular fitness in relation to all-cause mortality were
excluded because, although they provided important information, they did not directly
inform on the amount of physical activity associated with decreased risk of premature
mortality (additional discussion of studies on physical fitness and all-cause mortality is
provided later in this chapter). This left 73 studies that provide the evidence based for the
conclusions of this chapter. (Table G1.A1, which summarizes these studies, can be accessed
at http://www.health.gov/paguidelines/report/.)
Question 1: Is There an Association Between Physical Activity and
All-Cause Mortality? If So, What Is the Magnitude of This
Association?
Conclusions
The data very strongly support an inverse association between physical activity and
all-cause mortality. Active individuals — both men and women — have approximately a
30% lower risk of dying during follow-up, compared with inactive individuals. This inverse
association has been observed among persons residing in the United States, as well as in
other countries, older persons (aged 65 years and older), and persons of different race/ethnic
groups. In one study of persons with impaired mobility (unable to walk 2 km and climb
1 flight with no difficulty), physical activity also appeared to be associated with lower
all-cause mortality rates.
Rationale
Description of Studies in Evidence Base
Of the 73 studies included in the evidence base (Table G1.A1), 71 were prospective cohort
studies, 1 was a retrospective cohort study, and 1 was a case-control study. These studies
were conducted in many countries in North America, Europe, the Middle East, Asia, and
Australia. Twenty-seven studies, or 37%, were studies in the United States; the remaining
46 (63%) were conducted in other countries. The length of follow-up in the studies ranged
from 10 months to 28 years, apart from the one retrospective cohort study of Finnish
Olympic athletes, in which follow-up was 71 years (2). Across all studies, the median
follow-up was 11.7 years.
Physical Activity Guidelines Advisory Committee Report G1–2
Part G. Section 1: All-Cause Mortality
Population Subgroups
These studies provide a large database that included 312,554 observations in men and
690,671 observations in women, with a total of 140,114 deaths. Because several studies
published updated results in the same subjects, unique observations totaled 254,514 men and
576,574 women, and 113,358 deaths. Although the total number of women is larger than the
total number of men, this is skewed by 3 large studies of women (3-5); actually, fewer
studies included women (n=51), compared with studies that included men (n=62).
The youngest subjects included were aged 16 years (6), though most studies (44 of 73
studies, or 60%) included middle-aged subjects aged 40 years and older. A reasonable body
of evidence was specific to older persons aged 65 years and older, with 15 studies including
such subjects. With regard to race/ethnicity, among the US studies, most included only small
proportions of persons belonging to race/ethnic minority groups. However, 3 included
nationally representative samples of subjects (7-9) and another comprised 48.3% blacks
(10). In addition, 2 studies specifically enrolled Hispanic-American (11) and JapaneseAmerican men (12); 5 studies conducted in Asia enrolled Chinese and Japanese subjects
(4;13-16).
Most of the studies enrolled ostensibly healthy subjects who were free of cardiovascular
disease and cancer. However, several studies did select patient groups, including
patients with coronary artery disease (17) or at high risk (9;18), and patients with diabetes.
(7;19-22). In one study, subjects with impaired mobility were examined separately (23).
Main Findings
The available data strongly support an inverse relation between physical activity and
all-cause mortality rates during follow-up, with 67 of the 73 studies reporting a significant,
inverse relation for at least one group of subjects (e.g., men versus women) and/or one
domain of activity (e.g., all activity, exercise activity, or commuting activity).
With regard to the strength of association, the median relative risk (RR), comparing most
with least active subjects was 0.69 across all studies, indicating a 31% risk reduction with
physical activity. This was similar for men (median RR = 0.71) and women (median
RR = 0.67), and for studies where both sexes were analyzed together (median RR = 0.68).
The magnitude of association in this evidence base, which included studies published in
1995 and later, is similar to that reported in a 2001 review that included studies published
before 1995 (24).
An inverse association also existed among persons aged 65 years and older, with a median
relative risk of 0.56 when comparing most with least active persons. No significant
interaction was observed with race/ethnic groups in a study that included nationally
representative subjects (i.e., results did not differ across race/ethnic groups) (7). Inverse
associations also were noted among Puerto Rican men (11), Japanese-American men (12),
and Chinese and Japanese men and women living in Asia (4;13-16). Additionally, inverse
Physical Activity Guidelines Advisory Committee Report G1–3
Part G. Section 1: All-Cause Mortality
relations between physical activity and all-cause mortality were reported among patients
with coronary artery disease (17) or at high risk (9;18), and among patients with diabetes
(7;19-22). One study examined subjects with and without impaired mobility separately.
Among persons with impaired mobility, mortality rates also appeared lower among active
than inactive persons (this was not directly tested for statistical significance) (23).
Validity of Findings
Because all of the studies in the evidence base were observational epidemiologic studies
with no randomized controlled trials, the data cannot prove causality of effect. However, the
totality of evidence does support a cause-and-effect relation between physical activity and
lower all-cause mortality rates for the following reasons. First, as mentioned above,
plausible biological mechanisms — demonstrated in randomized clinical trials — exist for
physical activity to decrease the occurrence of cardiovascular disease and cancer, the leading
causes of mortality worldwide.
Second, bias due to decreased physical activity from ill health (i.e., a spurious inverse
relation, with ill health causing decreased physical activity, rather than physical activity
causing lower mortality rates) is unlikely. Many of the studies in Table G1.A1 included only
ostensibly healthy subjects and excluded persons with cardiovascular disease and cancer.
Studies that did include subjects with chronic diseases typically adjusted for the presence of
these conditions, and continued to observe inverse associations between physical activity
and all-cause mortality rates. Several studies also allowed for a lag period (i.e., excluding
initial years of follow-up) in analyses to minimize the potential bias from ill health leading
to decreased physical activity (as ill persons are likely to die early in follow-up); physical
activity was significantly related to lower all-cause mortality rates in these analyses. Finally,
if the follow-up period is long (which was typically the case, with the median follow-up
being 11.7 years), the impact of this bias will be diluted, with ill persons dying early in
follow-up.
Third, bias due to systematic misclassification of physical activity is unlikely. It is true that
almost all of the studies collected physical activity information using self-reports by
subjects, and this is likely to be imprecise. However, because physical activity was assessed
prospectively in almost all the studies, any misclassification is likely to be random (leading
to dilution of results, rather than a systematic bias). Additionally, one study assessed
physical activity using doubly-labeled water, considered a gold standard for measuring
energy expenditure. This study did report an inverse relation between physical activity and
all-cause mortality rates (10).
Fourth, bias resulting from large losses to follow-up is unlikely. Although many studies did
not report follow-up rates, many of these studies used national systems to ascertain deaths
(e.g., National Death Index in the United States), which tend to be complete. Of the studies
that did report follow-up rates, these tended to be very high.
Physical Activity Guidelines Advisory Committee Report G1–4
Part G. Section 1: All-Cause Mortality
Finally, physically active persons tend to have other healthy habits as well, which may
confound the association of physical activity with all-cause mortality rates. This is unlikely
to have explained the inverse relation observed because the association persisted after
controlling for several potential confounders (including age, sex, race, education, smoking,
body mass index [BMI], alcohol, diet, personal and family medical history, and reproductive
variables in women) listed in Table G1.A1.
Physical Fitness and All-Cause Mortality
Studies of physical fitness and all-cause mortality were not reviewed in the same detail as
studies of physical activity because the former studies do not provide direct information that
can be translated to public health recommendations for physical activity (e.g., How much?
What intensity? What duration? What frequency?). However, physical fitness, which
includes cardiorespiratory fitness, is closely related to physical activity. In particular, among
most individuals and particularly in those who are sedentary, increases in physical activity
result in increases in cardiorespiratory fitness. Thus, cardiorespiratory fitness is an objective
and reproducible marker of recent physical activity patterns. The findings from studies of
cardiorespiratory fitness mirror those from studies of physical activity in showing inverse
associations with all-cause mortality (see Part G. Section 2: Cardiorespiratory Health for a
detailed discussion of this issue). In fact, the magnitude of association is stronger for studies
of cardiorespiratory fitness, which may be due in part to the higher precision of
measurement, as, most of these studies use objective measurements of fitness (instead of,
typically, self-reported physical activity). For example, in the Aerobics Center Longitudinal
Study, the relative risks for mortality among the most fit men and women were 0.49 and
0.37, respectively, while the associations for physical activity were much weaker (25). In a
recent review (26), the median relative risk for all-cause mortality, comparing most fit with
least fit men in 10 studies was 0.55; for women in 6 studies, this also was 0.55. Thus, the
findings from studies of physical fitness support those from studies of physical activity, with
regard to an inverse relation with all-cause mortality.
Question 2: What Is the Minimum Amount of Physical Activity
Associated With Significantly Lower Risk of All-Cause Mortality?
Conclusions
The studies in the evidence base have assessed different domains of physical activity
(including one of more of the following: leisure-time activity, occupational activity,
household activity, and commuting activity), with most assessing primarily leisure-time
physical activity (LTPA), including walking. Some evidence indicates that it may be the
overall volume of energy expended — regardless of which activities produce this energy
expenditure — that is important to lower the risk of mortality. The studies also have used
different measures or units, such as kilocalories per week, metabolic equivalent
(MET)-hours per week, or hours per week to categorize physical activity levels in analyses.
Thus, combining the findings across studies posed a challenge.
Physical Activity Guidelines Advisory Committee Report G1–5
Part G. Section 1: All-Cause Mortality
In synthesizing the data across studies and expressing their findings in a fashion that can be
readily translated for public health purposes, the evidence base is clear in showing that the
equivalent of at least 2 to 2.5 hours per week of moderate-intensity physical activity is
sufficient to significantly decrease all-cause mortality rates (see Table G1.1, below). Several
studies investigated walking specifically, and it is reasonably clear that walking 2 or more
hours per week is associated with a significantly lower risk of all-cause mortality (see
Table G1.2, below). Additionally, faster pace of walking, compared with slower pace, is
associated with lower risk.
Table G1.1. Minimum Amounts of Physical Activity Associated With Significantly
Lower Risks of All-Cause Mortality
The data are presented according to different classifications of physical activity in the studies
reviewed. Within each classification scheme, studies are ordered according to their findings
regarding the minimum amount of activity observed to be associated with significantly lower risk of
all-cause mortality (lowest to highest).
Studies with subjects classified by energy expended in physical activity:
Reference Men Women
Both Sexes
Analyzed Together
Yu et al., 2003 (27) 23.9-2142.9 kcal/day
vigorous LTPA
(vs. 0-0.6 kcal/day)
– –
Lee et al., 1995 (28) 750-1499 kcal/wk
vigorous LTPA
(vs. <150 kcal/wk)
– –
Tanasescu et al.,
2003 (22)
12.1-21.7 MET-hr/wk
LTPA (vs. 0-5.1
MET-hr/wk); ≥16.1
MET-hr/wk walking
(vs. 0-1.4)
– –
Bucksch 2005 (29) – 14-<33.5 kcal/kg/wk
LTPA; i.e., ~910-2200
kcal/wk (65 kg woman)
(vs. 0 kcal/kg/wk)

Fried et al., 1998 (30) – – 980-1890 kcal/wk
LTPA (vs. ≤67.5
kcal/wk)
Lee & Paffenbarger
2000 (31)
1000-1999 kcal/wk
LTPA (vs. < 1000
kcal/wk)
– –
Janssen & Jolliffe 2006
(17)
– – 1000-1999 kcal/wk
LTPA (vs. < 500
kcal/wk)
Physical Activity Guidelines Advisory Committee Report G1–6
Part G. Section 1: All-Cause Mortality
Table G1.1. Minimum Amounts of Physical Activity Associated With Significantly
Lower Risks of All-Cause Mortality (continued)
Studies with subjects classified by energy expended in physical activity (continued):
Reference Men Women
Both Sexes
Analyzed Together
Lan et al., 2006 (15) – – 1000-1999 kcal/wk
LTPA (vs. < sedentary)
Haapanen et al., 1996
(32)
>2100 kcal/wk LTPA,
household activities,
commuting (vs. <800
kcal/wk)
– –
Matthews et al.,
2007 (4)
– 10.0-13.6 MET-hr/day
LTPA, work,
household, walking/
cycling commute
(vs. ≤9.9 MET-hr/day)

Manini et al., 2006 (10) – – >770 kcal/day all
activities (doublylabeled water)
(vs. <521 kcal/day)
Carlsson et al., 2006
(33)
– >50 MET-hr/day LTPA,
work, household,
walking/cycling
(vs. <35 MET-hr/day)

Studies with subjects classified by duration of physical activity:
Reference Men Women
Both Sexes
Analyzed Together
Bijnen et al.,1999 (34) At least 20 min/day,
3 day/wk walking and
cycling (vs. lesser
amount)
– –
Rockhill et al., 2001
(35)
– 1-1.9 hr/wk moderateto vigorous LTPA
(vs. <1 hr/wk)

Gregg et al., 2003 (7) – – ≥2 hr/wk walking
(vs. none)
≥2 hr/wk LTPA
(vs. none)
Landi et al., 2004 (36) – – ≥2 hr/wk LTPA and
chores (vs. <2 hr/wk)
Physical Activity Guidelines Advisory Committee Report G1–7
Part G. Section 1: All-Cause Mortality
Table G1.1. Minimum amounts of physical activity associated with significantly
lower risks of all-cause mortality (continued)
Studies with subjects classified by duration of physical activity (continued):
Reference Men Women
Both Sexes
Analyzed Together
Mensink et al.,
1996 (37)
>2 hr/wk sports
(vs. none)
– –
Leon et al., 1997 (18) 140 min/day LTPA
(vs. 4.9 min/day)
– –
Schooling et al.,
2006 (16)
– – ≤30 min/day LTPA
(vs. none)
Hu et al., 2004a (3) – ≥3.5 hr/wk moderate-to
vigorous LTPA
(vs. ≤0.5 hr/wk)

Fujita et al., 2004 (13) – ≥1 hr/day walking
(vs. ≤0.5 hr/day)

Studies with subjects classified by frequency of physical activity:
Reference Men Women
Both Sexes
Analyzed Together
Sundquist et al.,
2004 (38)
– – Occasional LPTA
(vs. none)
Lam et al., 2004 (14) 1/mo to 1-3/wk LTPA
of ≥30 min (vs. <1/mo)
1/mo to 1-3/wk LTPA
of ≥30 min (vs. <1/mo)

Kushi et al., 1997 (39) – Few/mo to 1/wk to
moderate LPTA
(vs. never/rarely)

Hillsdon et al.,
2004 (40)
– – 1/wk vigorous
sports/recreation
(vs. <1/mo)
LTPA, leisure-time physical activity
Table G1.2. Walking and All-Cause Mortality
For each study, the data* presented are for the lowest walking level significantly associated
with decreased relative risk of all-cause mortality. For studies without significant results, the
non-significant relative risk (shown in bold italics) associated with the highest walking level is given.
Further, the studies are grouped according to different classifications of walking in the studies
reviewed. Within each classification scheme for walking, studies are ordered from lowest to highest
walking level.
Physical Activity Guidelines Advisory Committee Report G1–8
Part G. Section 1: All-Cause Mortality
Table G1.2. Walking and All-Cause Mortality (continued)
Studies with subjects classified by energy expended on walking:
Reference Men Women
Both Sexes
Analyzed Together
Tanasescu et al.,
2003 (22)
≥16.1 MET-hr/wk
(vs. 0-1.4):
RR = 0.60 (0.41-0.88)
– –
Matthews et al.,
2007 (4)
– ≥7.1 MET-hr/day
(vs. 0.3.4):
RR = 0.86 (0.75-
1.05)

Studies with subjects classified by time spent walking:
Reference Men Women
Both Sexes
Analyzed Together
Gregg et al., 2003 (7) ≥2 hr/wk (vs. 0):
RR = 0.61 (0.48-0.78)
≥2 hr/wk (vs. 0):
RR = 0.71 (0.59-0.87)

Stessman et al.,
2000 (41)
– – ~4 hr/wk (vs. <4
hr/wk):
RR = 0.41 (0.19-0.91)
LaCroix et al.,
1996 (42)
– – >4 hr/wk:
RR = 0.91 (0.58-1.42)
Fujita et al., 2004 (13) ≥1 hr/day (vs. ≤0.5):
RR = 0.91 (0.80-1.04)
≥1 hr/day (vs. ≤0.5):
RR = 0.75 (0.62-0.90)

Wannamethee et al.,
1998 (43)
>60 min/day (vs. 0):
RR = 0.62 (0.37-1.05)
– –
Schnohr et al.,
2007 (44)
>2 hr/day (vs. <0.5):
RR = 0.80 (0.59-1.10)
>2 hr/day (vs. <0.5):
RR = 0.89 (0.69-1.14)

Studies with subjects classified by distance walked:
Reference Men Women
Both Sexes
Analyzed Together
Smith et al., 2007 (21) – – ≥1 mile/day (vs. 0):
RR = 0.89 (0.67-1.18),
normoglycemics
RR = 0.54 (0.33-0.88),
diabetics
Hakim et al., 1998 (12) 1.0-2.0 miles/day
(vs. <1)
RR = 0.68 (no CI
provided)
– –
Physical Activity Guidelines Advisory Committee Report G1–9
Part G. Section 1: All-Cause Mortality
Table G1.2. Walking and All-Cause Mortality (continued)
Studies with subjects classified by distance walked (continued):
Reference Men Women
Both Sexes
Analyzed Together
Lee & Paffenbarger
2000 (31)
≥12.5 miles/wk
(vs. <3.1):
RR = 0.84 (0.75-0.94)
– –
Studies with subjects classified by pace of walking:
Reference Men Women
Both Sexes
Analyzed Together
Davey Smith et al.,
2000; (45)
Batty et al., 2002; (19)
Batty et al., 2003 (46)
P, trend across slower,
the same, faster pace
(compared to others)
all < 0.01
– –
Schnohr et al., 2007
(44)
Average walking pace
(vs. slow):
RR = 0.75 (0.61-0.92)
Average walking pace
(vs. slow):
RR = 0.54 (0.45-0.67)

Studies with subjects classified by walking/cycling combined:
Reference Men Women
Both Sexes
Analyzed Together
Bijnen et al., 1998 (47) ≥20 min, 3 days/wk:
RR = 0.71 (0.58-0.88)
– –
Barengo et al.,
2004 (48)
≥30 min/day commute
(vs. <15):
RR = 1.07 (0.98-1.17)
≥30 min/day commute
(vs. <15):
RR = 0.98 (0.88-1.09)

Hu et al., 2004b (20) – – ≥30 min/day commute
(vs. 0):
RR = 0.88 (0.75-1.04)
Carlsson et al.,
2006 (33)
– >1.5 hr/day (vs. almost
never):
RR = 0.58 (0.45-0.75)

*Data shown are relative risk, RR (95% CI).
Physical Activity Guidelines Advisory Committee Report G1–10
Part G. Section 1: All-Cause Mortality
It is important to note that this amount — 2 to 2.5 hours per week of moderate-intensity
physical activity — does not represent a threshold level for risk reduction. Rather, the data
consistently support an inverse dose-response relation for the total volume of energy
expended, supporting a “some is good; more is better” message (see discussion under
Question 3 below).
Rationale
Assessment of Physical Activity
The different studies reviewed in this chapter primarily have used questionnaires to assess
physical activity. These questionnaires were different across the various studies and assessed
one or more domains of physical activity — leisure-time, household, occupation, and
commuting activity — with most assessing primarily leisure-time physical activity. In
analyses, the studies classified subjects using different classification schemes, such as by
energy expended, duration of activity, and frequency of activity. Several studies classified
subjects by ordinal groupings of physical activity (e.g., groups denoted as “sedentary,”
“light,” “moderate,” and “heavy”), but the amount of activity attributable to each category
was unclear. Thus, combining the data across studies and translating the findings into a
fashion that could be readily translated for public health purposes was challenging. Future
studies should attempt to collect detailed information on physical activity, as well as
categorize this in ways that make comparison across studies feasible. One helpful strategy
may be to use standardized units, such as energy expenditure (e.g., MET-hours per week) of
duration in activities of specified intensity (e.g., hours per week of moderate-intensity
physical activity).
Minimum Amount of Physical Activity Needed
Table G1.1 lists the studies with quantifiable amounts of physical activity, and shows that
most of the physical activity assessments were derived from leisure-time activities. For
studies classifying subjects by energy expended, it appears that some 1,000 kilocalories per
week or 10 to 12 MET-hours per week (approximately equivalent to 2.5 hours per week of
moderate-intensity activity) or more is needed to significantly lower the risk of all-cause
mortality. For studies classifying subjects by the duration of their physical activity, it
appears that some 2 hours per week or more is needed for significantly lower risks. A few
studies classified subjects by the frequency of physical activity (with or without duration
built in). These sparse data show that even 1 per month to 1 to 3 times per week of physical
activity, lasting at least 30 minutes in duration, is significantly associated with lower risk.
Across all studies, the minimum amount of activity did not appear to differ for men and
women.
Walking
Many studies have included walking in their assessment of physical activity, although
several combined this activity into an overall estimate of physical activity (e.g., as
kilocalorie energy expenditure). In recent years, however, investigators have been interested
Physical Activity Guidelines Advisory Committee Report G1–11
Part G. Section 1: All-Cause Mortality
in walking as an activity to be promoted for public health, and several studies have
presented data specifically on walking in relation to all-cause mortality rates.
Table G1.2 summarizes the findings from studies that have specifically investigated
walking. In these studies, investigators classified walking according to the energy expended
on walking, the time spent walking, the distance walked, the pace of walking, and walking
combined with bicycling, primarily for the purpose of commuting. Only 2 studies examined
the energy expended on walking and all-cause mortality rates; the data are inconsistent.
With regard to the time spent walking, for which most data are available, the findings are
reasonably consistent in showing that walking some 2 or more hours per week is associated
with a significantly lower risk. A small body of data suggests that walking 1 to 2 miles per
day is associated with lower risk. Additionally, faster pace of walking, compared with
slower pace, is consistently associated with lower risk. Few data are available on walking or
cycling as part of active commuting in relation to all-cause mortality, with investigators
typically examining 30 minutes or more per day of active commuting versus lesser levels.
These data are inconsistent and do not indicate that 30 minutes or more per day of active
commuting is associated with lower risk.
What Activities “Count”?
As mentioned previously, the studies reviewed in this chapter that have shown an inverse
relation between physical activity and all-cause mortality primarily have assessed leisuretime physical activity, including walking. However, some evidence indicates that it may be
the overall volume of energy expended — regardless of where this energy is derived —that
is important to lower the risk of mortality. Studies that have attempted to assess the total
amount of energy expended in leisure-time, occupational, household activity, and
commuting activity have reported significant inverse associations with the overall volume of
physical activity, as well with most of the individual domains analyzed separately (except
for commuting activity). These studies have included the Swedish Mammography Cohort
Study (33) and the Shanghai Women’s Health Study (4). In the Shanghai Women’s Health
Study (Figure G1.1), as amounts of energy expended on what investigators termed
“nonexercise activities” (i.e., activities other than leisure-time activity, including household
chores, walking and cycling as part of commuting, and climbing stairs) increased, rates of
all-cause mortality declined steadily.
Within each category of “nonexercise activities,” the addition of “regular exercise” (i.e.,
regular leisure-time physical activity) further reduced risk, except at the highest level of
nonexercise energy expenditure. This observation is compatible with the postulated doseresponse relation between physical activity and all-cause mortality, described in detail under
Questions 3 and 4 below. That is, the dose-response is likely curvilinear such that at higher
levels of energy expended, the curve flattens out. So in the Shanghai Women’s Health
Study, women at the highest level of nonexercise activities may have been at the upper end
of the dose-response curve, and the addition of further amounts of energy expended on
exercise activities did not appreciably reduce all-cause mortality rates further.
Physical Activity Guidelines Advisory Committee Report G1–12
Part G. Section 1: All-Cause Mortality
Figure G1.1. Relative risks of all-cause mortality according to exercise and
nonexercise activities, Shanghai Women’s Health Study
0.0
0.2
0.4
0.6
0.8
1.0
1.2
H
az ar d ra tio
0 0 0 0 0 0 0 0
Non-exercise activities (MET-hours/day)
0-9.9 10-13.6 13.7-18.0 18+
No regular exercise
Regular exercise
Referent
Source: Matthews et al., 2007 (4), with permission
Values are hazard ratios and 95% confidence intervals.
Adjusted for age (years), marital status (yes, no), education (elementary school or less, junior high school, high school,
college/post-high school), household income (low, middle, high), smoking (ever, never), alcohol drinking (ever, never), number
of pregnancies, oral contraceptive use (ever, never), menopausal status (yes, no), and several chronic medical conditions,
such as diabetes (yes, no), hypertension (yes, no), respiratory disease (yes, no; asthma, chronic bronchitis, or tuberculosis),
and chronic hepatitis (yes, no).
Figure G1.1. Data Points
Non-exercise
activities
(MET-hrs/d)
No regular
exercise
Hazard Ratio
No regular
exercise
(95% CI)
Regular
exercise
Hazard Ratio
Regular
exercise
(95% CI)
0–9.9 1.00 – 0.78 (0.62–0.99)
10–13.6 0.77 (0.62–0.95) 0.67 (0.54–0.83)
13.7–18.0 0.65 (0.52–0.81) 0.47 (0.36–0.61)
18.1+ 0.61 (0.49–0.77) 0.57 (0.44–0.74)
Physical Activity Guidelines Advisory Committee Report G1–13
Part G. Section 1: All-Cause Mortality
Further support for the premise that all activities “count,” and that it is the total amount of
energy expended that is relevant for all-cause mortality, comes from the Health ABC study
(10). In this study, which objectively measured total energy expenditure using doublylabeled water, the relative risk for all-cause mortality was significantly lower (0.65) among
men and women who expended more than 770 kilocalories per day in physical activity,
compared with less than 521 kilocalories per day. (The energy expended in physical activity
was estimated as: [total energy expenditure*0.90] — resting metabolic rate; i.e., assuming
the thermic effect of food to be 10%.) Among those expending 521 to 770 kilocalories per
day, the relative risk was 0.64, well below 1.0 but not statistically significant, which is a
likely consequence of reduced power due to the small number of deaths (n=55) in this study.
Findings from Studies of Physical Fitness That Can Inform on the Minimum Amount
of Physical Activity Needed
As stated previously, studies of cardiorespiratory fitness and all-cause mortality do not
provide direct information on the minimum amount of physical activity needed. However,
these studies can provide indirect information, in that the physical activity levels of groups
of fit subjects, who have lower mortality rates compared with unfit subjects, can be
ascertained. In a large prospective cohort study where moderate and high levels of
cardiorespiratory fitness were associated with lower rates of all-cause mortality, compared
with low levels of fitness in both men and women, the physical activity levels of subjects
were obtained by questionnaire (49). Men in the moderate and high cardiorespiratory fitness
groups reported an average of 130 and 138 minutes per week of walking, respectively.
Among women, the corresponding amounts were 148 and 167 minutes per week,
respectively. Thus, these data are compatible with data from the overall body of literature on
physical activity and all-cause mortality, which suggest that walking at least 2 hours per
week is needed to significantly lower mortality rates.
Question 3: Is There a Dose-Response Relation Between Physical
Activity and All-Cause Mortality?
Conclusions
The dose-response relation can be assessed with respect to specific dimensions of physical
activity, such as the total volume of energy expended, the intensity of the physical activity
carried out, the duration of physical activity, or the frequency of physical activity. The
largest amount of data, as well as the clearest, pertains to the total volume of energy
expended. These data consistently show an inverse dose-response relation between volume
of energy expended and all-cause mortality. Thus, while the answer to Question 2 above
indicates that at least 2 to 2.5 hours per week of moderate-intensity physical activity is
needed to significantly decrease all-cause mortality rates, this amount does not represent a
minimum threshold level for risk reduction. Rather, the dose-response relation for the total
volume of energy expended supports a “some is good; more is better” message. Some data
indicate that among populations where physical activity levels are likely to be low (e.g.,
middle-aged and older women, older men), significantly lower mortality rates are observed
Physical Activity Guidelines Advisory Committee Report G1–14
Part G. Section 1: All-Cause Mortality
at levels below 2 to 2.5 hours per week of moderate-intensity physical activity. Taken as a
whole, the data support a target of 2 to 2.5 hours per week of moderate-intensity physical
activity for lowering all-cause mortality rates, yet also encourage any level of activity below
the target for inactive groups of individuals.
Limited data suggest that vigorous-intensity physical activity is associated with additional
risk reduction compared with lower-intensity activities, beyond its contribution to the total
energy expended. There are no data to clarify dose-response relations for duration and
frequency of physical activity that are independent of their contributions to the total volume
of energy expended. In other words, it is unknown whether multiple, short bouts of physical
activity versus a single, long bout that expends the same energy are differentially associated
with all-cause mortality rates.
Rationale
The concept of “physical activity” is complex, in that it includes many different aspects,
such as the kinds of activities carried out, the intensity with which they are conducted, and
their duration and frequency. In examining the dose-response relation between physical
activity and all-cause mortality, we can investigate the association with regard to several
specific dimensions of physical activity: the total volume of energy expended, the intensity,
the duration, or the frequency. The dose-response relation for each of these dimensions is
discussed separately below.
Dose-Response Relation for Total Volume of Physical Activity
As Table G1.A1 indicates, the studies reviewed have used different methods (primarily
questionnaires, which differed across studies) to assess physical activity. However, all of
them possessed a measure that reflected the total volume of energy expended. This is
because any assessment of physical activity, no matter how simple, provides some
indication of the total volume of energy expended. For example, in the NHANES I
Epidemiologic Follow-up Study (50), physical activity during recreation was assessed by
asking, “Do you get much exercise in things you do for recreation, or hardly any exercise, or
in between?” Response options were: much exercise, moderate exercise, and little or no
exercise. Although it is impossible to equate the different activity categories to actual
kilocalories or MET-hours of energy expended, it is clear that the categories represent
ordered levels representing the total volume of physical activity.
Of the studies reviewed, 59 of the 73 studies classified subjects according to at least 3 levels
of physical activity, allowing for assessment of dose-response related to the total volume of
energy expended. Among these 59 studies, 33 reported significant, inverse trends between
physical activity and all-cause mortality rates. Another 21 studies showed apparent inverse
trends that were not formally tested for statistical significance. The remaining 5 studies
showed a non-significant trend (n=1) or apparent lack of trends that were not formally tested
for significance (n=4).
Physical Activity Guidelines Advisory Committee Report G1–15
Part G. Section 1: All-Cause Mortality
As discussed above under Question 2, at least 2 to 2.5 hours per week of moderate-intensity
physical activity is needed to significantly decrease all-cause mortality rates. However,
rather than representing a minimum threshold level for risk reduction, the dose-response
relation for the total volume of energy expended indicates that though this is a desired
minimum level of physical activity, risk reductions already begin to occur below this level,
supporting a message of “some is good; more is better.” Additionally, some data indicate
that among populations where physical activity levels are likely to be low (e.g., middle-aged
and older women, older men) significantly lower mortality rates are observed at levels
below 2 to 2.5 hours per week of moderate-intensity physical activity. In a study of
middle-aged and older women, significantly lower rates of mortality were observed among
women engaging in 1 to 1.9 hours per week of moderate-to-vigorous intensity leisure-time
physical activity (35). In another study of older men and women aged 65 years and older,
“occasional” leisure-time physical activity also was associated with significantly lower
mortality rates (38). This association also held true for walking or cycling for at least 20
minutes, 3 days a week, among men aged 64 to 84 years (47).
Further support for the “some is good; more is better” message comes from a recent
randomized clinical trial of physical activity to increase cardiorespiratory fitness levels —
higher levels of which are associated with lower all-cause mortality rates — among
sedentary, postmenopausal women (51). In this trial, a dose-response relation was observed
such that graded increased in fitness were observed for 3 groups exercising at 50%, 100%,
and 150% of the Surgeon-General’s recommendation (with 100% being equivalent to
150 minutes per week of moderate-intensity physical activity). Thus, these data support a
target of 2 to 2.5 hours per week of moderate-intensity physical activity for lowering
all-cause mortality rates, yet also encouraging any level of activity below the target for
inactive groups of individuals.
Dose-Response Relation for Intensity of Physical Activity
In 11 studies, investigators examined the dose-response relation for intensity of physical
activity. All but one reported significantly reduced risks for vigorous-intensity activity
compared with lesser-intensity physical activity. However, the interpretation of these
findings is not straightforward because the intensity of physical activity is related to the total
volume of energy expended. That is, when carried out for the same total duration,
higher-intensity physical activities expend more total energy than do lower-intensity
physical activities. Thus, if studies do not account for this correlation, it is unclear whether
the significantly reduced risk associated with vigorous-intensity physical activity can be
attributed to the intensity of the activity, or whether it is merely due to the increase in the
total volume of energy expended (i.e., confounding of intensity by volume of energy
expended). In other words, for the same volume of energy expended, does vigorous intensity
activity confer additional benefits compared to moderate- or light-intensity activity?
Of the 11 studies, 4 did attempt to account for confounding by the volume of energy
expended. All 4 reported significant, inverse dose-response relations with intensity of
physical activity. Thus, these limited data suggest that higher intensities of physical activity
Physical Activity Guidelines Advisory Committee Report G1–16
Part G. Section 1: All-Cause Mortality
are associated with additional risk reductions for all-cause mortality, beyond their
contribution to greater total volume of energy expended.
Dose-Response Relation for Duration and Frequency of Physical Activity
Longer duration of physical activity, as well as greater frequency of physical activity, results
in greater total volume of energy expended, compared with shorter durations or lower
frequencies of activity. However, just as with the dose-response relation to the intensity of
physical activity, the relation between dose and duration or frequency has the potential to be
confounded by the total volume of energy expended. Therefore, the total volume must be
taken into account in order to make conclusions regarding duration and frequency that are
independent of the total volume of energy expended.
Ten studies examined the dose-response relation between duration of physical activity and
all-cause mortality. These studies indicated that longer durations of activity were associated
with lower mortality rates. However, these studies did not adjust for confounding by volume
of physical activity and so the data on duration may be reflecting the dose-response relation
between the total volume of energy expended and risk of all-cause mortality. These data
cannot provide any conclusion regarding whether multiple, short bouts of physical activity
versus a single, long bout that expends the same energy are differentially associated with
all-cause mortality rates.
Three studies examined the dose-response relation for frequency of physical activity. Again,
these studies did not adjust for confounding by volume of physical activity; thus, the data on
frequency may be reflecting findings for the dose-response of total volume of energy
expended and all-cause mortality rates. These data also cannot clarify the relative benefits of
multiple, short bouts of physical activity versus a single, long bout that expends the same
energy for all-cause mortality rates.
Finally, 1 study examined the association of all-cause mortality and physical activity carried
out 1 to 2 days a week and that generates sufficient energy expenditure to meet current
physical activity recommendations (i.e., the so-called “weekend warrior” pattern) (52).
Overall, the relative risk for mortality among weekend warriors, compared with sedentary
men, was 0.85 (95% confidence interval [CI], 0.65, 1.11). In stratified analysis, however,
among men without major cardiovascular risk factors, weekend warriors had a significantly
lower risk of dying, compared with sedentary men (RR = 0.41 [0.21, 0.81]). This was not
seen among men with at least 1 major risk factor (corresponding RR = 1.02 [0.75, 1.38]).
Question 4: What Is the Shape of the Dose-Response Relation
Between Physical Activity and All-Cause Mortality?
Conclusions
The dose-response curve relating different amounts of physical activity to all-cause
mortality rates appears curvilinear. On average across studies, compared to less than
Physical Activity Guidelines Advisory Committee Report G1–17
Part G. Section 1: All-Cause Mortality
0.5 hours per week of moderate-to-vigorous physical activity, engaging in approximately
1.5 hours per week of such activity is associated with about a 20% reduction in risk.
Additional amounts of activity are associated with additional risk reductions, but at smaller
magnitudes, such that an additional approximately 5.5 hours per week is required to observe
a further 20% in risk (i.e., approximately 7.0 hours per week is associated with about a 40%
reduction in risk, compared with less than 0.5 hour per week).
Rationale
To describe the dose-response curve in detail, studies in which subjects were classified into
at least 5 categories of physical activity were selected. Eleven studies defined 5 levels of
physical activity; one defined 6 levels. Figure G1.2 shows the dose-response curve for each
of the 12 studies. These categories were defined according to ordinal levels of activity
(5;43), the frequency of activity (38), the time per week spent in physical activity (35), or
the energy expended on physical activity (either as kilocalories per week, MET-hours per
week, or MET-hours per day)(15;17;22;28;30;31;33;53). In a first analysis, we did not
attempt to quantify the amount of physical activity, but merely designated these categories
as 1 to 6, and plotted the relative risks of all-cause mortality associated with each of these
categories. In general, these studies support a curvilinear shape to the dose-response curve.
Next, we attempted to synthesize the results across the different studies to obtain an
“average” shape of the dose-response curve. Because the physical activity categories
represented different amounts of physical activity, we translated them, where possible, into a
common measure of hours per week spent on moderate-to-vigorous physical activity. We
excluded from the analysis the one study that had 6 categories of physical activity because it
used ordinal groupings that did not allow interpretation of the amount of physical activity.
For the remaining studies, we assigned to each of their 5 categories of physical activity the
median value of that category, in hours per week of moderate-to-vigorous physical activity.
We plotted the median relative risk of all-cause mortality against each of these 5 categories
of physical activity.
Figure G1.3 shows that this analysis supports the curvilinear shape observed for most of the
individual studies in Figure G1.2. The largest risk reduction is seen at the lowest end of the
physical activity spectrum, and additional risk reductions — at smaller magnitudes — are
seen at higher levels of physical activity. On average, it appears that compared to less than
0.5 hour per week of moderate-to-vigorous physical activity, engaging in approximately
1.5 hours per week of such activity is associated with about a 20% reduction in risk of
all-cause mortality. Additional amounts of physical activity are associated with additional
risk reductions, but at smaller magnitudes, such that an additional approximately 5.5 hours
per week are required to observe a further 20% decline in risk (i.e., approximately 7.0 hours
per week is associated with approximately 40% reduction in risk, compared with less than
0.5 hour per week).
Physical Activity Guidelines Advisory Committee Report G1–18
Part G. Section 1: All-Cause Mortality
Figure G1.2. Shape of the Dose-Response Curve: Relative Risks of All-Cause
Mortality by Physical Activity Level (Studies With at Least 5 Levels
of Physical Activity)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
R
el at iv e R
is k of A
llC
au se M
or ta lit
y 1 2 3 4
Level of Physical Activity
5
Lee 95 Fried 98 Kujala 98
Wannamethee 98 Lee 00 Rockhill 01
Tanasescu 03 Sundquist 04 Trolle-Lagerros 05
Carlsson 06 Janssen 06 Lan 06
Figure G1.2. Data Points
Author/Year Level 1 Level 2 Level 3 Level 4 Level 5 Level 6
Lee 95 1 0.88 0.92 0.87 0.87
Fried 98 1 0.78 0.81 0.72 0.56
Kujala 98 1 0.85 0.72 0.68 0.6
Wannamethee 98 1 0.79 0.69 0.64 0.63 0.54*
Lee 00 1 0.8 0.74 0.8 0.73
Rockhill 01 1 0.82 0.75 0.74 0.71
Tanasescu 03 1 0.88 0.64 0.64 0.65
Sundquist 04 1 0.72 0.6 0.5 0.6
Trolle-Lagerros 05 1 0.78 0.62 0.58 0.46
Carlsson 06 1 0.49 0.43 0.41 0.39
Janssen 06 1 0.87 0.77 0.54 0.63
Lan 06 1 0.8 0.74 0.5 0.43
*Not shown.
Physical Activity Guidelines Advisory Committee Report G1–19
Part G. Section 1: All-Cause Mortality
Figure G1.3. “Median” Shape of the Dose-Response Curve
0.0
0.2
0.4
0.6
0.8
1.0
1.2
R
el at iv e R
is k of A
llC
au se M
or ta lit
y 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Moderate to Vigorous Leisure-Time Activity, Hr/Wk
Figure G1.3. Data Points
Hr/wk RR
0.5 1
1.5 0.8
3 0.73
5.5 0.64
7 0.615
Question 5: Is the Relation Between Physical Activity and
All-Cause Mortality Independent of Adiposity?
Conclusions
The inverse relation between physical activity and all-cause mortality appears independent
of adiposity. Further, this inverse relation appears to hold regardless of whether subjects are
normal weight, overweight, or obese.
Physical Activity Guidelines Advisory Committee Report G1–20
Part G. Section 1: All-Cause Mortality
Rationale
Debate exists regarding whether adiposity should be adjusted for when examining the
relation between physical activity and all-cause mortality rates. The argument against
adjusting is that adiposity represents one pathway through which physical activity favorably
influences mortality rates; thus, adjustment for adiposity minimizes the effect of physical
activity. Nonetheless, almost 60% of the studies (43 of 73) adjusted their results for BMI or
some other measure of adiposity (e.g., weight or waist-hip ratio). These studies, after
adjustment for adiposity, continued to observe significant, inverse associations between
physical activity and all-cause mortality.
Additionally, a few studies have stratified their findings by BMI, to examine the relation
between physical activity and all-cause mortality among subjects with different BMI
(3;11;31;54). These studies indicate that the inverse association between physical activity
and all-cause mortality holds for persons who are normal weight, overweight, and obese. For
example, among men in the Harvard Alumni Health Study (31), compared with inactive and
overweight men, those who were active but overweight had a relative risk of 0.80 (95% CI,
0.71-0.91). Corresponding results were 0.90 (0.79-1.02) for men who were inactive but of
normal weight, and 0.67 (0.60-0.75) for active and normal weight men. Among women in
the Nurses’ Health Study (3), using normal weight, active women as referent, normal
weight women who were inactive had an elevated relative risk of dying during follow-up,
1.55 (1.42-1.70). Using the same referent, the relative risk for overweight, active women
was 1.28 (1.12-1.46); for overweight, inactive women, this was 1.64 (1.46-1.83). For obese,
active women, the relative risk was 1.91 (1.60-2.30); for obese and inactive women, this was
2.42 (2.14-2.73).
Overall Summary and Conclusions
The overall conclusions of this chapter on physical activity and all-cause mortality may be
summarized as the following:
• A large body of scientific evidence, all from observational epidemiologic studies,
exists on the association of physical activity with all-cause mortality rates.
• The data very consistently show an inverse relation, with the most active
individuals — both men and women — experiencing approximately a 30% reduction
in risk of mortality during follow-up, compared with the least active.
• The inverse relation extends to older persons, aged 65 years and older.
• Although this inverse relation has been observed in many countries throughout the
world, the data that are specific to non-white populations are limited compared to
those on white populations. The inverse relation appears to be similar for both white
and non-white populations.
Physical Activity Guidelines Advisory Committee Report G1–21
Part G. Section 1: All-Cause Mortality
• Studies primarily have assessed leisure-time physical activity, including walking.
There is, however, some evidence to indicate that it may be the overall volume
of energy expended — regardless of which activities produce this energy
expenditure — that is important to lower the risk of mortality.
• With regard to the minimum amount of physical activity needed, it appears that at
least 2 to 2.5 hours per week of moderate-intensity physical activity are required to
significantly lower all-cause mortality rates. Walking has been specifically
investigated in several studies, and it also appears that walking at least 2 hours per
week is associated with significantly lower all-cause mortality rates.
• However, this amount — 2 to 2.5 hours per week of moderate-intensity physical
activity — does not represent a minimum threshold level for risk reduction. The data
consistently support an inverse dose-response relation for the total volume of energy
expended, which supports a “some is good; more is better” message. In particular,
the data support a target of 2 to 2.5 hours per week of moderate-intensity physical
activity for lowering all-cause mortality rates, and encourage any level of activity
below this target for inactive groups of individuals.
• It appears that the shape of the dose-response curve is curvilinear (see Figure G1.2).
On average across studies, compared to less than 0.5 hour per week of moderate-tovigorous physical activity, engaging in approximately 1.5 hours per week of such
activity is associated with about a 20% reduction in risk. Additional amounts of
activity are associated with additional risk reductions, but at smaller magnitudes,
such that another approximately 5.5 hours per week is required to observe a further
20% decline in risk (i.e., approximately 7.0 hours per week is associated with about a
40% reduction in risk, compared with the risk associated with less than 0.5 hour per
week).
• Limited data support vigorous-intensity physical activity being associated with
additional risk reduction, compared with lower intensity activities, beyond its
contribution to the total volume of energy expended.
• No data are available to inform whether multiple, short bouts of physical activity
versus a single, long bout that expends the same energy are differentially associated
with all-cause mortality rates.
• Finally, the inverse relation between physical activity and all-cause mortality appears
independent of adiposity. Importantly, this inverse relation appears to hold regardless
of whether subjects are normal weight, overweight, or obese.
Physical Activity Guidelines Advisory Committee Report G1–22
Part G. Section 1: All-Cause Mortality
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Physical Activity Guidelines Advisory Committee Report G1–26
Part G. Section 1: All-Cause Mortality
Physical Activity Guidelines Advisory Committee Report G1–27
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Part G. Section 2:
Cardiorespiratory Health
Introduction
Cardiovascular diseases (CVD) account for the majority of premature morbidity and
mortality in the developed world. The influence of physical activity and the prevention and
treatment of cardiovascular disease is therefore of great importance. In considering the
effects of physical activity on cardiovascular health, one must address not only its influence
on the development of symptomatic disease (e.g., heart attack and stroke) but also the
influence on risk factors that are known to contribute to the development of symptomatic
disease and are often indicative of sub-clinical asymptomatic vascular pathology. Most of
the modifiable risk factors for cardiovascular diseases are metabolic in nature and are, in
turn, modifiable by changes in physical activity. These metabolic risk factors include
hypertension, atherogenic dyslipidemia, the axis of insulin resistance to metabolic syndrome
to frank type 2 diabetes, and obesity. In turn, both physical inactivity and poor
cardiorespiratory fitness are major risk factors for cardiovascular diseases.
Review of the Science
Overview of Questions Addressed
In this critical review of the knowledge base about the relations between cardiovascular
disease and physical activity, cardiovascular disease should be construed to include coronary
heart disease, cerebrovascular disease, and peripheral arterial disease. This section of the
report reviews the data regarding this relation in two parts, sequentially addressing a series
of questions about the presence and the nature of the relationship between physical activity
and cardiorespiratory health. First, the section addresses the primarily observational data
about physical activity and cardiovascular disease in separate sections dealing with coronary
heart disease, cerebrovascular disease and stroke, and peripheral arterial disease. Then, using
data from experimental studies, it explores the evidence of the relation between physical
activity and several cardiovascular disease risk markers: hypertension, atherogenic
dyslipidemia, vascular health and cardiorespiratory fitness. Influences of physical activity on
insulin resistance, glucose control, metabolic syndrome and diabetes are addressed in
Part G. Section 3: Metabolic Health and relations between physical activity and obesity are
addressed in Part G. Section 4: Energy Balance. Within each disease or risk factor
Physical Activity Guidelines Advisory Committee Report G2–1
Part G. Section 2: Cardiorespiratory
category, this section reviews the supporting evidence and provides conclusions about the
following 3 questions.
1. What is the nature of the relationship with physical activity?
2. What is known about the dose-response relationship with different characteristics of
physical activity?
3. What is known about whether the effects of physical activity exposure can be
obtained in smaller multiple bouts per day (accumulation) versus single daily bouts?
Data Sources and Process Used To Answer Questions
The Cardiorespiratory Subcommittee focused its review on studies performed since the
publication of the Surgeon General’s Report on Physical Activity and Health in 1996 (1),
emphasizing disease prevention as opposed to disease treatment. The subcommittee drew
heavily from the Physical Activity Guidelines for Americans Scientific Database (see
Part F: Scientific Literature Search Methodology, for a detailed description of the
Scientific Database). In addition, the subcommittee relied on expert knowledge of the
authors to identify specific published studies that are critical for the knowledge base that
may predate 1996, post-date the collation of the Scientific Database, or for outcomes that
were not identified as part of the Scientific Database process (e.g., vascular health markers).
Also, reviews in some subject areas (hypertension and atherogenic dyslipidemia) relied in
part upon meta-analyses. Finally, for some topics (e.g., cardiorespiratory fitness), separate
literature searches were performed in the PubMed database.
All of the prospective cohort and case-control studies included in this review provide
self-report information on the habitual physical activity of the subjects, a standardized
assessment of CVD clinical events and a comparison of event rates in subjects assigned to
2 or more categories of physical activity. For interventional experimental studies, the
analysis was restricted to randomized controlled trials (RCTs) that had a sedentary
(non physical activity intervention control arm or period) and studied at least 25 subjects
per arm, unless the findings were highly significant with a lower number.
In general, the reviews and discussions address physical activity performed in the context of
dedicated sessions of exercise. The assumption is that the specified exercise activity is
performed in addition to and on top of normal physical activity performed as a part of
activities of daily living. The data are primarily confined to dynamic aerobic (endurance)
exercise, as the long-term cardiovascular prevention benefits of resistance and flexibility
exercises are relatively little studied to date (2). An exception to this approach occurs when
measures of total activity or occupational activity are use as exposure variables in
prospective cohort or case-control studies.
Physical Activity Guidelines Advisory Committee Report G2–2
Part G. Section 2: Cardiorespiratory
Special Considerations and Limitations
The relation between dynamic aerobic exercise and cardiovascular health outcomes,
including cardiorespiratory fitness is complex and can be thought of as a series of point
estimates within a 3-dimensional matrix of continuous variables: exercise exposure, disease
activity, and the magnitude of the response. The major limitation to exercise exposure
recommendations for cardiovascular health outcomes is that any recommendation poorly
conveys the concept that the location of any point estimate along each of these 3 axes is
along a continuum of exposure and response, and should not be viewed as an absolute
threshold below which no benefits accrue and above which benefits always accrue.
Continuum of Exercise Exposure
It is well accepted that aerobic exercise exposures can be characterized by an interaction
between bout intensity, frequency, duration, and longevity of the program (3;4). The product
of these characteristics can be thought of as volume and can be represented by the total
energy expenditure (EE) of the exercise exposure. Exercise volume is referred to as the
major focus of the exercise recommendation in some recent statements (5), thus allowing for
the mixing of exercise bouts of varying intensity, frequency and duration. As
recommendations are intended to be adopted for an individual’s life-time, longevity is not
considered here. However, it is clear that most benefits resulting from changes in physical
activity and exercise patterns accrue over days, weeks, months and even years of exposure,
and that the study and understanding of such time lines are of scientific and clinical interest
and should be investigated further. Most of the data from experimental studies presented
here regarding dose-response associations address the issue of varying intensities of exercise
and do not control for bout duration, frequency, or total volume of the exercise exposure. In
most observational studies, the major variable used as an exposure is activity amount (e.g.,
minutes, metabolic equivalent [MET]-minutes per day, miles per week) with the other
exposure frequently being activity intensity. However, because total weekly EE usually is
not controlled, it is possible that the effects of higher intensities observed in these studies
might reflect the higher volumes performed, and that the volume of the activity exposure is
the important operative. As will be apparent from the relation of exercise volume to the
other variables, one cannot fix volume and also simultaneously study either intensity,
frequency, or duration effects while controlling the other two. Relatively few interventional
experimental studies examine exercise intensity while controlling for EE and even fewer
study frequency or duration effects while controlling for EE. This makes the construction of
a precise exercise dose for any given response problematic.
Continuum of Disease Progression
Cardiovascular disease is a continuum from asymptomatic fatty vascular streaks, to severe
symptomatic coronary heart disease, to fatal myocardial necrosis and death. The same is true
for cerebrovascular disease and stroke. The goal of this section is to focus primarily on
primary cardiovascular disease prevention. As part of that process, we have explored some
Physical Activity Guidelines Advisory Committee Report G2–3
Part G. Section 2: Cardiorespiratory
treatment effects on cardiovascular risk factors (e.g., atherogenic dyslipidemia and
hypertension), the favorable modulation of which, by pharmacologic or lifestyle therapy,
have been shown to be related to reductions in cardiovascular risk as well. The modulation
of these risk markers may be the mechanism through which physical activity acts to reduce
cardiovascular clinical events, as well. One should be aware that the activity exposure
beneficial for primary cardiovascular health (the factors studied in this chapter) and
prevention may or not apply to patients with clinically active and apparent cardiovascular
disease, such as those in rehabilitation programs.
Role of Physical Inactivity in Disease Progression
A note about the importance of acknowledging the health risks of inactivity in studies of the
effects of physical activity on cardiovascular risk factors is indicated here. In studies that
include a sedentary inactive non-intervention control group for comparison to the exercise
intervention groups, the inactive group consistently tends to demonstrate a worsening in
health parameters over time. This is the health cost of physical inactivity, to be contrasted
with the health benefits of regular physical activity. That is, the lack of physical activity in
normal life leads to worsening in some parameters absent other life style changes, such as in
diet. In some instances, the lack of worsening in some parameters over time demonstrated in
intervention groups would appear to be an indication that the exercise or physical activity
intervention has no effect, whereas, in fact, when compared to inactive control groups, a
significant difference in response over time is observed.
Continuum of the Response
The response of biological parameters to dynamic aerobic exercise, and likely to resistance
training as well, is a continuum from undetectable changes to highly significant, robust and
clinical important ones that are highly dependent on the exercise exposure variables
previously discussed. Consequently, it is likely that no given minimal intensity, frequency,
duration or volume of exercise will result in a favorable response for any given outcome.
Similarly, it is unlikely that any of these exercise variables has a level for optimal outcome.
Furthermore, increases in exercise exposure do have tangible adverse outcomes that are
primarily musculoskeletal and cardiovascular (see Part G. Section 10: Adverse Events).
Thus, potential increases in favorable outcomes of increasing exercise exposure must be
balanced by the potential for increases in unfavorable outcomes.
Question 1: What Is the Relationship Between Physical Activity
and Cardiovascular Morbidity and Mortality?
Conclusion
The results of recently published studies continue to support a strong inverse relation
between the amount of habitual physical activity performed and CHD and CVD morbidity
or mortality. For both men and women at middle age or older, remaining sedentary is a
Physical Activity Guidelines Advisory Committee Report G2–4
Part G. Section 2: Cardiorespiratory
major independent risk factor, with persons reporting moderate amounts of activity having a
20% lower risk and those reporting activity of higher amounts or intensity having
approximately a 30% lower risk than least active persons. These may be underestimates of
the risk reductions (with the underestimate being on the order of 10%) because multivariate
models in many studies include adjustments for hypertension, dyslipidemia, and glucose
tolerance, conditions that may represent biological intermediates in the causal pathway.
Although still limited, data also indicate habitual physical activity benefits the
cardiovascular health of people of various races and ethnicities.
Introduction
Physical Activity and Health: A Report of the Surgeon General concluded by saying, “The
epidemiologic literature supports an inverse association and a dose-response gradient
between physical activity level or cardiorespiratory fitness and both CVD in general and
CHD in particular. A smaller body of research supports similar findings for hypertension.
The biological mechanisms for these effects are plausible and supported by a wealth of
clinical and observational studies. It is unclear whether physical activity provides a
protective role against stroke” (1, p.112). Since 1996, a large volume of research has been
directed at better defining the relation between physical activity and various CVD clinical
outcomes, the mechanisms by which the cardiovascular benefits of physical activity are
likely mediated, and the characteristics of the dose of activity (type, intensity, frequency,
session duration, and total volume) associated with lower CVD clinical event rates.
The following material provides an overview of the scientific literature since 1996 directed
at establishing the effects of physical activity on various clinical cardiovascular outcomes
and the issue of dose-response. The main focus is on the primary prevention of clinical
events; therefore, most of the evidence comes from prospective cohort studies of at-risk
populations. All of the studies included in this review provide self-report information on the
habitual physical activity of the subjects, a standardized assessment of cardiovascular
clinical events, and a comparison of event rates in subjects assigned to 2 or more categories
of physical activity. These comparisons consisted of a measure of the relative risk (RR) for
the groups and 95% confidence intervals for the measure of risk, including risk ratios,
hazard ratios or odds ratios. In all the cited studies, the multivariate adjusted relative risks
were recorded and used in any analysis. These adjustments varied from study to study but
usually included at a minimum age, body mass index (BMI), cigarette smoking, blood
pressure, and blood lipid concentrations. It is understood that using multivariate
adjustments, which in some cases include measures of BMI, blood pressure, and blood
lipids, could inappropriately decrease the magnitude of the relation between the physical
activity exposure and the clinical outcome because some of the benefit of the activity might
be mediated through these variables (“intermediate” or “mediator” variables). However, we
considered this a more conservative approach than adjusting just for age and other selected
demographic variables. In studies where RRs for more active versus the least active persons
are presented using both limited adjustments and multivariate adjustments that accounted for
potential “intermediate” variables, the RRs for limited adjustments show greater effects in
Physical Activity Guidelines Advisory Committee Report G2–5
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–6
the range of 10% (6-8). To determine whether a dose-response pattern existed between
physical activity characteristics and the clinical outcome, data for at least 3 activity
categories needed to be provided. The Physical Activity Guidelines for Americans Scientific
Database was used to identify eligible studies published between January 1996 and June
2007. Also, selected studies that did not meet criteria for inclusion in the Database but
provided ancillary data related to specific issues have been considered in this review,
including meta-analyses and systematic reviews.
Rationale
Between January 1995 and June 2007, more than 60 studies were published that met the
subcommittee’s search criteria investigating the effects of habitual physical activity on
cardiovascular morbidity and/or mortality in men and women throughout a wide age span
and of various race and ethnicities. Much of the self-reported physical activity was
performed during leisure time, but also included are data from occupational, household, and
commuting activities. A majority of these data come from prospective cohort studies with
the results from a limited number of case-control studies included. Studies tended to report
outcomes for various clinical manifestations of coronary heart disease (e.g., fatal or nonfatal
myocardial infarction, ischemic heart disease, cardiac death), a more general category of
cardiovascular disease that could include a variety of manifestations of atherothrombotic
vascular disease (e.g., coronary heart disease, stroke, other vascular disorders), and stroke or
cerebrovascular disease. Data were organized from these studies by CHD, CVD, and stroke
and then by sex with an emphasis on the magnitude of any relation and whether evidence of
a dose response existed. The relation between a measure of physical activity and a CVD
clinical outcome was considered significant if the 95% confidence interval did not include
1.0. A significant dose-response relation usually was based on P for trend being <0.05.
Coronary Heart Disease
The results of studies investigating the relation between habitual physical activity and CHD
morbidity and/or mortality published since 1996 quite consistently show lower event rates in
more physically active men and women than for their least active counterparts. Most notable
has been the large increase in the number of studies that have included data on women, with
19 studies reporting data on women and 9 with data on men and women combined (see
Table G2-1 for a summary of the studies and Table G2-A1 for selected data from individual
studies) (Table G2-A1 can be accessed at http://www.health.gov/paguidelines/report/).
The studies of women reporting CHD clinical events included more than 200,000 subjects
aged 20 to 85 years. For the prospective cohort studies, the median RR of having a CHD
clinical event for women reporting participation in moderate intensity or amount of physical
activity compared to women reporting no or only light intensity activity was 0.78, while the
RR for women performing vigorous or high amounts of activity as compared to women
eporting no or light activity was 0.62. These RRs are quite similar to those resulting from a
Part G. Section 2: Cardiorespiratory
Table G2.1. Summary of Prospective Cohort Studies and Case-Control Studies Published in the English Language Since
1996 Reporting on the Relation Between Habitual Physical Activity and the Prevention of Coronary Heart
Disease, Cardiovascular Disease, or Stroke
Data summaries for each study in this review are included in the Appendix.
Men
Condition
Prevented
Prospective
Cohort
Studies
Number of
Studies
Reporting RR
Prospective
Cohort
Studies
Median RR
M/L
Prospective
Cohort
Studies
Median RR
H/L
Prospective
Cohort
Studies
Number of
Studies
Reporting
D-R
Prospective
Cohort
Studies
Number of
Studies
D-R Sig.
CaseControl
Studies
Number of
Studies
Reporting
RR
CaseControl
Studies
Median
RR M/L
CaseControl
Studies
Median
RR H/L
CaseControl
Studies
Number of
Studies
Reporting
D-R
CaseControl
Studies
Number
of Studies
D-R Sig.
Coronary Heart
Disease 17 0.81 0.68 11 7 6 0.65 0.53 2 2
Cardiovascular
Disease 10 0.78 0.70 3 2 1 0.65 0.67 0 0
Total Stroke 11 0.65 0.72 6 5 0 – – – –
Women
Condition
Prevented
Prospective
Cohort
Studies
Number of
Studies
Reporting RR
Prospective
Cohort
Studies
Median RR
M/L
Prospective
Cohort
Studies
Median RR
H/L
Prospective
Cohort
Studies
Number of
Studies
Reporting
D-R
Prospective
Cohort
Studies
Number of
Studies
D-R Sig.
CaseControl
Studies
Number of
Studies
Reporting
RR
CaseControl
Studies
Median
RR M/L
CaseControl
Studies
Median RR
H/L
CaseControl
Studies
Number of
Studies
Reporting
D-R
CaseControl
Studies
Number
of Studies
D-R Sig.
Coronary Heart
Disease 13 0.78 0.62 8 5 6 0.62 0.44 3 1
Cardiovascular
Disease 12 0.80 0.72 6 5 1 0.89 0.71 0 0
Total Stroke 8 0.82 0.72 5 4 0 – – – –
Physical Activity Guidelines Advisory Committee Report G2–7
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–8
Table G2.1. Summary of Prospective Cohort Studies and Case-Control Studies Published in the English Language Since
1996 Reporting on the Relation Between Habitual Physical Activity and the Prevention of Coronary Heart
Disease, Cardiovascular Disease, or Stroke (continued)
Men and Women (Data Combined)
Condition
Prevented
Prospective
Cohort
Studies
Number of
Studies
Reporting RR
Prospective
Cohort
Studies
Median RR
M/L
Prospective
Cohort
Studies
Median RR
H/L
Prospective
Cohort
Studies
Number of
Studies
Reporting
D-R
Prospective
Cohort
Studies
Number of
Studies
D-R Sig.
CaseControl
Studies
Number of
Studies
Reporting
RR
CaseControl
Studies
Median
RR M/L
CaseControl
Studies
Median RR
H/L
CaseControl
Studies
Number of
Studies
Reporting
D-R
CaseControl
Studies
Number
of Studies
D-R Sig.
Coronary Heart
Disease 5 0.74 0.63 1 1 4 0.61 0.48 3 1
Cardiovascular
Disease 5 0.87 0.72 2 1 0 – – – –
Total Stroke 4 0.67 0.75 2 1 2 0.68 0.48 0 0
D-R, dose-response; H/L, high intensity or high amount vs. light intensity/amount; M/L, moderate intensity/amount vs. light intensity/amount; RR, relative risk (includes risk ratio, odds
ratio or hazard ratio); Sig., significant.
Part G. Section 2: Cardiorespiratory
meta-analysis of many of the same studies that were published between 1996 and 2003 (9).
The conclusion from this meta-analysis for CHD was that physical activity was associated
with a lower risk of CHD (as well as CVD and stroke) in a dose-response fashion with
pooled RRs for both moderate amounts and high amounts being significant when compared
to no or light activity. In the 6 case-control studies reported for women, the median RR was
0.62 for moderate versus no or light activity and 0.44 for vigorous intensity or high amounts
of activity versus no or light activity.
Of the studies reporting on CHD in men, 16 were prospective cohort studies and 4 were
case-control studies. Approximately 124,000 men aged 15 to 96 years at baseline were
included as subjects. Most studies reported on leisure-time physical activity (LTPA) with a
few studies including occupational activity, commuting, and sports participation. Among the
prospective cohort studies, the median RR was 0.81 for moderate intensity or amount of
activity versus no or light activity and 0.68 for vigorous intensity or high amounts versus
light or no activity. For the 6 case-control studies, the median RR was 0.65 for moderate
versus no or light activity and 0.53 for vigorous intensity or high amounts versus no or light
activity. These values are of a similar magnitude to those reported in a systematic review of
studies published between 1953 and 2000 (10) and in a meta-analysis published in 2001 that
included data from studies published before and after the Surgeon General’s Report on
Physical Activity and Health (11). The lower CHD event rate for more active men was
reported for both nonfatal and fatal CHD with no systematic difference in CHD incidence
versus CHD mortality.
Five prospective cohort studies and 4 case-control studies were published in which the
results for CHD events for men and women were combined. In the prospective cohort
studies, the median RR was 0.74 for moderate intensity or amount versus no or light activity
and 0.63 for high intensity or amount versus no or light activity. In the case-control studies,
the RR was 0.61 for moderate activity versus no or light activity and 0.48 for high amounts
or intensity versus no or light activity.
Cardiovascular Disease
In prospective cohort studies published since 1996 that included data on the relation between
habitual physical activity and CVD in women (n=12), the median RR was 0.80 for those
reporting moderate intensity or amount versus no or light activity and 0.72 for vigorous
versus no or light activity. In the one case-control study reporting on CVD in women, the
RR was 0.89 for moderate intensity versus no or light activity and 0.71 for high versus no or
light activity. (See Table G2-A2 for selected data from these prospective cohort and casecontrol studies. This table can be accessed at http://www.health.gov/paguidelines/report/.)
Here again, the amount and quality of data evaluating the relation between physical activity
and CVD clinical events in women has substantially increased since 1996, with at least
350,000 women included in the reported studies. Overall, the CVD data reported on men are
very similar to those for women: In 10 prospective cohort studies the median RR for CVD
events was 0.78 for moderate versus no or light activity and 0.70 for high intensity or
amount versus no or light activity. In the one case-control study, the RR was 0.65 for
Physical Activity Guidelines Advisory Committee Report G2–9
Part G. Section 2: Cardiorespiratory
moderate versus light activity and 0.67 for high versus no or light activity. Although data are
not provided in the reports, it is very likely that a majority of the CVD events included in
these studies were the result of coronary heart disease.
Effects of Sex, Age, or Race and Ethnicity
Although the magnitude of median RRs for CHD for both moderate versus light activity and
high versus light activity are somewhat lower in women than in men (Table G2-1),
physically active men and women both typically have a lower risk for CHD than do their
least active counterparts. Comparisons between the sexes are difficult across studies because
of some evidence that the activity levels in the least active women are less than for the least
active men, age distributions within age categories (e.g., 40 to 65 years, 65 to 79 years) are
different from study to study, and CHD event rates within age categories differ between men
and women. In the studies that included data for both men and women (12-20), even fewer
presented results for men and women separately and in some studies that do, the number of
CHD events in women is relatively small, thus substantially limiting the reliability of any
analysis (19). In a case-control study published by Fransson and colleagues (20) evaluating
the association between various types of physical activity and acute myocardial infarction,
women appeared to be somewhat more protected than men. The RR for fatal and nonfatal
MI in women comparing most active versus least active for total activity was 0.16 (95% CI
0.07-0.37), and the RR for the same comparison in men was 0.46 (95% CI 0.31-0.69). For
women, the RR for LTPA more than 3 times per week versus seldom was 0.31 (95% CI
0.15-0.66); for men the RR was 0.53 (95% CI 0.38-0.73). It should be noted that rarely is a
distinction made in these studies between associations in pre- and post-menopausal women,
and whether they are different in these two populations when studied separately.
Consequently, no evidence exists that effects of physical activity on CHD are different
whether the study population is men, pre-menopausal, or post-menopausal women.
The inverse association between physical activity and CHD events has been reported for
adults across a wide range of ages, with the magnitude of the association for older men and
women (aged 65 years and older) at least as strong as for younger adults. Because CVD
morbidity and mortality rates are low in men younger than age 45 years and women younger
than age 55 years, very few data are available on the relation between physical activity
levels and CVD clinical events in younger adults or youth. None of the meta-analyses on
physical activity and CVD events published since 1995 has evaluated the effect of age on
the magnitude of the relation, and only a limited number of studies have compared different
age categories within their population. Manson and colleagues (21) had a sufficiently large
sample of women (n=73,743) and cardiovascular events (n=1,551) in the Women’s Health
Initiative Observational Study to analyze the relation between LTPA and CVD incidence for
3 age groups, 50 to 59 years, 60 to 69 years, and 70 to 79 years. When activity was classified
by MET-hours per week in quintiles, all 3 age groups showed a significant difference (P for
trend <0.001) when the highest versus the lowest quintiles were compared (RR = 0.45, 0.50
and 0.64, respectively) with the lowest quintile being the reference (1.0) the adjusted RRs
for quintiles 2 through 5 for women aged 50 to 59 years were 0.68, 0.63, 0.54, 0.45,
respectively. For women aged 60 to 69, the RRs were 0.79, 0.63, 0.56, 0.50, respectively,
Physical Activity Guidelines Advisory Committee Report G2–10
Part G. Section 2: Cardiorespiratory
and for women aged 70 to 79, they were 0.93, 0.86, 0.75, 0.64, respectively. Other studies
have not showed any meaningful difference in the relation between physical activity level
and CVD events in different age categories. For example, women in the College Alumni
Health Study contrasting those younger than age 45 years versus those 45 years and older at
baseline (22), combined data on men and women contrasting aged 65 years and younger
versus those older than 65 years (23), or those aged 65 to 74 years versus aged 75 years and
older (24). In a small prospective cohort study in men evaluating various risk factors for
CHD, high-intensity activity was related to CHD events in those older than age 65 years
(0.36, 95% CI 0.13-1.05) but not in those aged 65 years and younger (25). In the Buffalo
Blood Pressure Study, older women (aged 60 years and older) were not protected from CVD
mortality by high levels of total activity, though physical activity provided some protection
for women younger than aged 60 years. However the number of CVD events was small in
both groups (26).
Few studies conducted in the United States have had an adequate sample size and clinical
outcomes to evaluate the association between physical activity and CVD clinical events in
race or ethnic groups other than non-Hispanic whites. The Women’s Health Initiative
Observational Study (21) included 61,574 white women and 5,661 black women with a
mean follow-up of 3.2 years. The relation between total physical activity level (quintiles of
MET-hours per week) and CVD clinical events was significant for both groups of women
with RR for the highest versus lowest quintile of activity for white women being 0.56 (P for
trend <0.001) and for black women 0.48 (P for trend = 0.02). In contrast to these results, a
report on the Atherosclerosis Risk in Communities (ARIC) study population indicated that
although activity level and CVD clinical events had a significant inverse relation in white
men and women, no such relation was found for either back men or women (19). The
authors suggested that this lack of association in blacks may be due to the limited number of
blacks reporting vigorous physical activity (5% in black men versus 15% in white men).
However, outside the United States, where the relation between physical activity level and
CVD clinical events has been evaluated in other race and ethnic populations, there is no
indication that the favorable association frequently reported for non-Hispanic white men and
women does not occur in other race and ethnic populations. For example, physically active
Japanese men and women living in Japan (27) and older Japanese men living in Hawaii (28)
had lower CVD mortality rates than the least active. Similar results have been reported for
Chinese women living in Shanghai (29) and Chinese men and women living in Hong Kong
(30). In a case-control study including men and women conducted in New Delhi and
Bangalore India, at least 145 MET-minutes per day of LTPA versus no activity had a RR for
myocardial infarction of 0.44 (95% CI 0.27-0.41). Time spent in non-work sedentary
activity also was directly associated with risk of myocardial infarction (the RR for at least
215 minutes per day of sedentary activity versus fewer than 70 minutes per day was 1.58
[95% CI 1.05-2.36]).
Change in Physical Activity and Cardiovascular Disease Clinical Events
Most reports from prospective observational studies have presented the relation between
physical activity measured on one occasion and the rate of CVD clinical events over various
Physical Activity Guidelines Advisory Committee Report G2–11
Part G. Section 2: Cardiorespiratory
periods of follow-up. However, a few studies have obtained self-reported activity 2 or more
times, typically 3 to 15 years apart, and related change in activity during this interval with
CVD clinical events during a follow-up period. The goal of this approach is to determine
whether an increase in activity is associated with lower event rates than observed for
subjects who remain inactive. Also, do subjects who move from an active to an inactive
category have higher CVD event rates than subjects who remain physically active? Men in
the Harvard Alumni Study who increased their physical activity index to 2,000 kilocalories
per week or more (measured in 1962 or 1964 and again in 1977) compared to men who
remained inactive had a 17% lower CHD death rate (P= 0.51), while men who took up
moderately vigorous sports had a 41% lower risk (P= 0.04) (31). Similar results have been
reported for British men. Those who reported an increase in activity over 12 to 14 years had
a RR for CVD mortality of 0.66 (95% CI 0.35-1.23) compared to men who remained
sedentary, while men who remained active had a RR of 0.54 (95% CI 0.31-0.94) compared
to continuously sedentary men (32).
Women in the Nurses’ Health Study who reported increases in their LTPA between 1980
and 1986 with follow-up to 1994 had lower CVD event rates than women who remained
sedentary (6). When the increase in activity for women who were sedentary in 1980 was
expressed in quartiles of METs, the RRs for quartile 1 through quartile 4 were 0.85, 0.79,
0.67 and 0.71, respectively (P for trend=0.03). Women aged 65 years of age and older who
had physical activity assessed twice (5.7 years apart) and changed from being inactive to
active had a RR for CVD mortality of 0.64 (95% CI 0.42-0.97) compared to women who
remained inactive, and women who remained active had a RR of 0.68 (95% CI 0.58-0.82).
Although data on the association between change in activity and CVD clinical events in
prospective observational studies does not provide the same level of evidence as data from
RCTs, these results do add to the strength of the evidence linking higher levels of physical
activity with lower CVD risk. In the studies cited, the change in activity preceded the
clinical events and the direction of the association is consistent with an increase in activity
causing a reduction in risk.
Question 2: What Are the Dose-Response Relations Between
Physical Activity and Cardiovascular Morbidity and Mortality?
Conclusion
The inverse association between CVD clinical events and habitual physical activity exists
across a wide range of types, amounts, and intensities of activity. People at highest risk are
those who are least active and spend much of their day in activities that consume low
amounts of energy. When compared to very sedentary persons, men and women who
perform small amounts of moderate-intensity activity, such as 60 minutes per week of
walking at a brisk pace, exhibit fewer CVD clinical events. People who perform more
activity and/or at a faster pace are at an even lower risk, with much of the benefit derived
when men and women are performing 150 or more minutes per week of moderate-intensity
(3 to less than 6 METs) physical activity. Greater amounts of activity appear to provide
Physical Activity Guidelines Advisory Committee Report G2–12
Part G. Section 2: Cardiorespiratory
greater benefit but the shapes of any dose-response relations have not been well defined.
Vigorous-intensity activity (equal to or more than 6 METs) when performed for a similar
duration as moderate-intensity activity results in greater energy expenditure and is
associated with lower CVD event-rates. Much of the recent data are based on LTPA, but
performing physical activity during an occupation, around the home, or while commuting all
appear to provide benefit as well.
Rationale
In the studies reporting on CHD or CVD, the median RR difference for high levels of
activity versus inactive or light activity categories was somewhat greater than the difference
in the median RR for moderate levels of activity versus inactive or light activity, thus
indicating a somewhat greater benefit from higher amounts or intensities of activity versus
moderate intensity and amounts of activity. In the cohort studies that had 3 or more physical
activity levels, authors frequently evaluated dose-response by calculating the linear trend
and testing this trend for significance. If the P for trend was ≤0.05, then the dose response
was considered significant. For CHD in women, 7 studies reported P values for dose
response, and 3 of them were significant. Six studies reported dose response for CVD in
women, with 5 reaching significance. For men, 7 of 11 studies reporting dose response for
CHD were significant as were 2 of the 3 studies reporting on CVD. For studies that
combined data on men and women, the one study that reported dose-response for CHD
found it to be significant, and 1 of the 2 studies reporting on CVD was significant.
From a public health perspective, it is important to recognize that when the reference group
in the population being studied is very sedentary, modest amounts of moderate intensity
activity are associated with significantly reduced rates of CHD and CVD. For example, in 3
large prospective cohort studies of women in the United States (6;7;21), those who walked
in the range of 1 to 2 hours per week versus non-walkers produced RRs for CVD or CHD
events of 0.75 (95% CI 0.63-0.89; (21), 0.70 (95% CI 0.51-0.95; (6)), and 0.49 (95% CI
0.28-0.86; (7)) (Figure G2-1). The P for trend with multivariate adjustment for categories of
walking amount (MET-minutes per week or duration (minutes per week) was significant
(P <0.001) in all 3 studies. Also, walking at a faster pace was associated with a lower risk of
CHD or CVD in these 3 studies, with those who walked at a pace 3.0 miles per hour and
greater having a significantly lower RR than non-walkers (0.76, 0.70 and 0.52). The P for
trend across walking pace was significant for all 3 studies. Other studies have reported on
walking and CVD with either significantly lower RRs for men and women who walk
regularly versus non-walkers (24) or favorable but non-significant trends for increased
walking (22;28;33;34). There was no difference in a large study of Chinese women living in
Shanghai where the least active reference group included walking from 0 to 3.4 MET-hours
per week (29). In this study, the amount of walking in the reference group of Chinese
women was sufficiently high that additional walking may not provided additional protection
against CVD. Overall, these data on walking and CVD indicate that when brisk walking is
performed 3 hours per week by otherwise sedentary persons, especially women, the CVD
clinical event rate is significantly lower than for persons who do little walking or other
physical activities.
Physical Activity Guidelines Advisory Committee Report G2–13
Part G. Section 2: Cardiorespiratory
Figure G2.1 Relative Risk of CVD in Women — Walking Amount/Week
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1 2 3 4 5
<0.5 0.6-2.0 2.1-3.8 3.9-9.9 ≥10.0 <0.001
0 0.1-2.5 2.6-5.0 5.1-10.0 >10.0 <0.001
MET-hrs/wk
MET-hrs/wk
Min/week
Quintile P for trend
0 1-59 60-90 >120 <0.001
Manson, 1999 (6)
Manson, 2002 (21)
Lee, 2001 (7)
Figure G2.1. Data Points
Studies 1 2 3 4 5
Manson, 1999 1 0.78 0.88 0.7 0.65
Manson, 2002 1 0.91 0.75 0.75 0.68
Lee, 2001 1 0.86 0.49 0.48
Physical Activity Guidelines Advisory Committee Report G2–14
Part G. Section 2: Cardiorespiratory
Question 3: What Is the Relationship Between Physical Activity
and Cerebrovascular Disease and Stroke?
Conclusion
More physically active men and women generally have a lower risk of stroke incidence or
mortality than the least active, with more active persons demonstrating a 25% to 30% lower
risk for all strokes. A favorable relation exists between physical activity level and stroke
(both for ischemic and for hemorrhagic stroke), but the data on these stroke subtypes are still
quite limited. The benefits appear to be derived from a variety of activity types, including
activity during leisure time, occupational activity, and walking. Overall, the relationship
between activity and stroke is not influenced by sex or age, and very little data exist for race
and ethnicity other than for non-Hispanic whites.
Rationale
The Surgeon General’s Report on Physical Activity and Health concluded that “the existing
data do not unequivocally support an association between physical activity and stroke risk”
(1, p.103). This conclusion was based on a review of 14 observational studies (4 included
women), of which 8 showed an inverse relationship between physical activity and stroke.
The other studies showed no significant association, with 2 studies suggesting a U-shaped
relationship with higher stroke risk in the least and most active categories. Since 1996,
studies meeting the criteria for this review include data from studies on women (n=8), men
(n=11), and men and women combined (n=6). (See Table G2-A3 for selected data from
these prospective cohort and case-control studies. This table can be accessed at
http://www.health.gov/paguidelines/report/.) In addition, 2 meta-analyses of physical
activity and stroke have been published (35;36). In most studies, data are reported on all
strokes, and in some studies data also are provided separately for ischemic and hemorrhagic
stroke. In women, the median RR was 0.82 for all strokes combined for moderate-intensity
activity versus no or light activity and 0.72 for high-intensity or amount versus no or light
activity. For all strokes in men, the median RR was 0.65 for moderate-intensity versus no or
light activity and 0.72 for high-intensity or amount versus no or light activity. In the studies
reporting combined data on men and women, the median RR for the prospective cohort
studies (n=4) was 0.67 for moderate-intensity versus no or light activity and 0.75 for highintensity or amount versus no or light activity. For the 2 case-control studies, the median RR
was 0.68 for moderate versus low activity and 0.48 for high versus low activity.
The meta-analysis by Wendel-Vos and colleagues (36) included data from 31 studies
published in English before 2001, including 24 prospective cohort studies and 7 case-control
studies. Based on these analyses, the authors concluded that moderately active men and
women had lower rates of ischemic, hemorrhagic, and all strokes than did the least active
subjects. When persons who reported moderate-intensity occupational activity were
compared with persons who reported light-intensity occupational activity, the RR was 0.64
(95% CI 0.48-0.87). They also observed an RR of 0.85 (95% CI 0.78-0.93) for moderate
Physical Activity Guidelines Advisory Committee Report G2–15
Part G. Section 2: Cardiorespiratory
versus light LTPA. High-level occupational activity appears to protect against ischemic
stroke compared with both moderate (0.77, 95% CI 0.60-0.98) and inactive occupational
levels (0.57, 95% CI 0.60-0.98). Persons reporting high-level compared to low-level LTPA
were at significantly lower risk for all strokes (0.78, 95% CI 0.71-0.85), ischemic stroke
(0.79, 95% CI 0.69-0.91), and hemorrhagic stroke (0.74, 95% CI 0.57-0.96). Both
moderately active men and women had a lower RR for hemorrhagic stroke than their
inactive counterparts (men = 0.54, 95% CI 0.36-0.81; women = 0.76, 95% CI 0.67-0.86;
P=0.07 for difference between men and women). Studies conducted in Europe showed a
stronger inverse association between active and inactive persons (0.47, 95% CI 0.33-0.66)
compared to studies conducted in the United States (0.82, 95% CI 0.75-0.90). The overall
results of the meta-analysis on physical activity and stroke published a year earlier (35) were
similar to the results of this meta-analysis. When Lee and colleagues included data from
both cohort and case-control studies, the RR for stroke incidence or mortality for the most
active versus the least active was 0.73 (95% CI 0.67-0.79) and for moderately active versus
the least active the RR was 0.80 (95% CI 0.74-0.86).
The inverse association between physical activity level and stroke risk appears very similar
for men and women in the few studies that report sex-specific data. Vatten and colleagues
(37) followed 34,868 Norwegian women and 32,872 men for 16 years and documented
cause-specific mortality. The P for trend for total activity and stroke mortality was 0.009 for
men and <0.001 for women, and the RR for high activity versus never active was significant
for both sexes. In Japan, 31,023 men and 42,242 women were followed for an average of 9.7
years, and walking and sports participation were inversely related to CVD mortality (27).
The relationship of walking time to all stroke or ischemic stroke mortality was very similar
for men and women as was the time spent in sports participation. Because the occurrence of
stroke is very low for those younger than age 55 years, very few reports are available on the
relation of physical activity to stroke morbidity or mortality in younger and middle-aged
populations. Data from the National Health and Nutrition Examination Survey
Epidemiologic Follow-up Study (38) indicate no systematic difference in the relationship of
LTPA amount to either total or non-hemorrhagic stroke in men or women aged 45 to 64
years versus 65 to 74 years at baseline (the age x low activity interaction term was not
significant). Overall, the strongest and most consistent association between activity level and
stroke in this study was seen in white women.
Although stroke rates tend to be higher in African American men and women than in other
race/ethnicities in the United States, no studies have adequately addressed the relation of
physical activity level and stroke risk in any race/ethnicity other than non-Hispanic whites.
Physical Activity Guidelines Advisory Committee Report G2–16
Part G. Section 2: Cardiorespiratory
Question 4: What Is the Relationship Between Physical Activity
and Peripheral Arterial Disease?
Conclusion
No large RCTs have been conducted to investigate exercise training in peripheral arterial
disease (PAD). Little is known regarding exercise dose response (intensity, duration or
frequency) or different modalities (walking, cycling, resistance training) of exercise to
prevent PAD because most of the studies have followed the same exercise prescription,
which has used supervised treadmill walking at a similar dose. Furthermore, even less is
known about how subpopulations differ in responses to exercise training, such as whether
sexes respond differently or whether an interaction exists between type 2 diabetes and
exercise responsiveness in persons with PAD.
Rationale
Exercise for Primary Prevention of Peripheral Arterial Disease
Only a handful of cross-sectional primary prevention studies have been performed to relate
ankle brachial index (ABI), an indicator of severity of peripheral lower extremity arterial
occlusion, with physical activity (Table G2-A4, which summarizes these studies, can be
accessed at http://www.health.gov/paguidelines/report/.) Activity questionnaires have been
used to examine retrospectively the relationship between physical activity and abnormal
ABIs. In the Edinburgh Artery Study (39), for example, the amount of physical activity
performed between the ages of 35 to 45 years was inversely related to prevalence of PAD at
ages 55 to 74 years, but only in men. Further, this relation held only for men who had
smoked at some time in the past. Gardner and colleagues (40) observed that the amount of
physical activity was related to ABI measures in those without PAD, suggesting that regular
habitual exercise may be related to the presence of sub-clinical asymptomatic PAD.
Exercise for Secondary Prevention of Peripheral Arterial Disease
Exercise training is a powerful secondary preventive measure for those with established
PAD (Tables G2-A5 and G2-A6, which summarize these studies, can be accessed at
http://www.health.gov/paguidelines/report/). Several meta-analyses and review articles
summarize this body of literature (Table G2-A7, which summarizes these studies, can be
accessed at http://www.health.gov/paguidelines/report/) (41-49). Although these studies
unequivocally demonstrate exercise training to be beneficial for improving maximal walking
ability, many lack necessary criteria such as large sample sizes, randomized and controlled
designs, assessments of sex and dose-response effects, and differential responses in
symptomatic (intermittent claudication) versus asymptomatic individuals needed to make
strong specific clinical exercise recommendations. Despite these shortcomings, the data
demonstrate that adherence to a structured supervised exercise program is currently regarded
as the most effective treatment for symptomatic PAD. In all of the clinical studies noted
above, the 2 most commonly measured variables used to determine the effectiveness of a
Physical Activity Guidelines Advisory Committee Report G2–17
Part G. Section 2: Cardiorespiratory
PAD therapy are peak walking time (PWT) and claudication onset time (COT). It is clear
that exercise improves both PWT and COT in patients with PAD (50-64).
Based on the evaluation of meta-analyses and clinical studies, the average improvement
following exercise training in PWT is near 100%, with COT improving consistently to an
even greater degree (to the magnitude of 130% or more). Other responsive variables,
primarily measured in small studies, are peak oxygen consumption, walking economy, daily
physical activity, 6-minute walk time, leg blood flow, and quality of life. Interestingly,
although some studies have demonstrated improved leg blood flow and ABI, these indices
have not convincingly been related to functional markers. It appears that improved oxidative
metabolism in the skeletal muscle may explain some of the improvements in exercise
tolerance (50;52). Whether increased growth of small blood vessels (angiogenesis) and
oxidative machinery (enzymes, mitochondria) are responsible for the improved muscle
metabolism following exercise training is being explored. Findings also suggest that
improvements can be augmented beyond those resulting from a traditional 12-week exercise
program. As much as an additional 50% improvement in PWT may be achieved with
continued therapy to up to 24 weeks (51). Twelve to 24 weeks of exercise training produced
improvements in free-living accelerometer-derived daily physical activity, walking economy
measured by constant workload oxygen consumption (slow component of VO2). Although a
traditional exercise prescription for PAD recommends that patients endure a moderate rather
than severe level of claudication pain during training bouts, limited evidence indicates that a
lower exercise intensity than the pain threshold elicits similar results as exercise above the
pain threshold as long as the same dose in minutes is maintained (63).
The Relationship Between Daily Physical Activity and Peripheral Arterial Disease
Studies have confirmed that the severity of PAD is related to daily free-living physical
activity. (Table G2-A8, which summarizes these studies, can be accessed at
http://www.health.gov/paguidelines/report/.) Studies show that, among individuals with
PAD, daily physical activity is reduced approximately 40% compared to matched healthy
controls and that the degree of claudication (as measured by ABI and PWT) is related to
daily physical activity within a PAD population (65;66). These findings have been
confirmed using accelerometers and performance score questionnaires that have related the
decrease in daily physical activity to impairments in the lower extremity. A progressive
decline in leisure-time activities of both moderate and high intensities has been identified in
individuals with PAD (67). The loss of daily physical activity corresponds with decreasing
ABI values and COT. Furthermore, a relation appears to exist between free-living physical
activity and microcirculation in the calf muscle (66). The natural progression of PAD has
been assessed and determined to be inversely related to self-reported physical activity as
assessed by COT, 6-minute walk test, and calf blood flow (68). All of these studies
demonstrate that, despite a lack of randomized controlled exercise studies to evaluate the
effect of exercise training on preventing PAD, a lack of exercise contributes to disease
progression, symptom status, and additional inactivity in those who have PAD.
Physical Activity Guidelines Advisory Committee Report G2–18
Part G. Section 2: Cardiorespiratory
Although most studies comparing supervised versus home-based programs conclude that
supervised exercise is better, this remains inconclusive. No study has investigated the effects
of an exercise program on asymptomatic patients with known PAD to determine whether
exercise can prevent the onset of claudication or disease worsening. In addition, little is
known about the role of resistance training, as no definitive trial has directly compared
traditional walking exercise to resistance training in the PAD population.
Question 5: What Is the Relationship Between Physical Activity
and Hypertension?
Conclusion
Both aerobic and progressive resistance exercise yield important reductions in systolic and
diastolic blood pressure (BP) in adult humans, although the evidence for aerobic exercise is
more convincing. Traditional aerobic training programs of 40 minutes of moderate- to
high-intensity exercise training 3 to 5 times per week and that involve more than 800 METminutes of aerobic exercise per week appear to have reproducible effects on BP reduction.
Rationale
In this section we update the evidence of the effects of chronic exercise on resting BP in
adults generated since the release of the Surgeon General’s Report on Physical Activity and
Health (1). This update is limited to a review of previous meta-analyses that met the
following criteria: (1) RCTs only, (2) meta-analyses published in the English language
between January 1, 1995 and September 30, 2007, (3) adults aged 18 years and older,
(4) aerobic or progressive resistance training as the only intervention, (5) non-intervention
control group, (6) resting or ambulatory systolic and diastolic BP as a primary outcome in
each meta-analysis.
Relationship Between Aerobic Exercise and Blood Pressure
Ten meta-analyses dealing with the effects of aerobic exercise on resting BP in adults have
been published since 1996 (69-78). Six of these meta-analyses were comprehensive
(69;72;74-77) and the remaining 4 focused on either women (71), older adults (73),
overweight and obese subjects (70), or walking as the only intervention (78). The most
recent and inclusive meta-analysis that included data partitioned according to hypertensive,
prehypertensive, and normotensive adults included a total of 72 studies, 105 exercise groups,
and 3,936 men and women with a between-study age range of 21 to 83 years (median age =
47 years) (76). Across all categories, mean reductions in resting BP ranged from 2 to 5
mmHg (2% to 4%) for resting systolic BP and 2 to 3 mmHg (2% to 3%) for resting diastolic
BP. Reductions were greater in hypertensive subjects (systolic BP, −6.9 mmHg; diastolic
BP, −4.9 mmHg) than in prehypertensive (systolic BP, −3.1 mmHg; diastolic BP, −1.7
mmHg) and normotensive (systolic BP, −2.4 mmHg; diastolic BP, −1.6 mmHg) subjects.
Changes were equivalent to relative reductions of approximately 5% for both resting systolic
and diastolic BP in hypertensive subjects, 1% (systolic BP) and 2% (diastolic BP) in
Physical Activity Guidelines Advisory Committee Report G2–19
Part G. Section 2: Cardiorespiratory
prehypertensive subjects, and 2% for both resting systolic and diastolic BP in normotensive
subjects. Significant reductions of 3.3 mmHg (2%) and 3.5 mmHg (4%) also were observed
for daytime ambulatory systolic and diastolic BP with no significant change in nighttime
BP. Changes in ambulatory BP are especially noteworthy because the assessment of the
measure may better predict target end-organ damage (79). Changes in both resting and
ambulatory BP were independent of changes in body weight (76). Similar changes in resting
BP also were found for the other inclusive meta-analyses (69;72;74-77) as well as metaanalyses that focused on women (71), older adults (73), overweight and obese subjects (70),
and walking (78).
Dose-Response Relations Between Aerobic Exercise and Blood Pressure
The vast majority of studies included in the meta-analyses conducted since the release of the
Surgeon General’s Report on Physical Activity and Health (1) have tended to follow
traditional guidelines for the prescription of aerobic exercise in adults as recommended by
the American College of Sports Medicine (5;80;81). For example, for the most recently
published meta-analysis dealing with the effects of aerobic exercise on resting BP (77), the
pooled median length of training was 16 weeks, with a frequency of 3 days per week.
However, the analysis included studies in which subjects exercised up to 7 days per week,
with a duration of 40 minutes per session and intensity of 65% of maximal heart rate
reserve. No consistent relations were observed between changes in resting systolic and
diastolic BP and the length, frequency, duration, and intensity of training (77). The most
common forms of exercise used in these RCTs were walking, jogging, and stationary
cycling, although other types of exercise, such as aerobic dance, also were included. Other
meta-analyses also have failed to find a relation between training program characteristics
and changes in resting BP (69-72;74-76;78). In contrast, one meta-analysis did report larger
decreases in resting systolic and diastolic BP with a greater duration (minutes) of training
per session as well as greater decreases in resting systolic BP with lower training intensities
(73).
Relation Between Progressive Resistance Exercise and Blood Pressure
Since the release of the Surgeon General’s Report on Physical Activity and Health (1),
3 meta-analyses (45;77;82) have been conducted on the effects of progressive resistance
exercise on resting systolic and diastolic BP. However, as 2 of these included the same data
(77;82), this discussion is limited to the one that contained more complete data on
progressive resistance training (82). This meta-analysis included 9 RCTs and 12 exercise
groups comprising 341 men and women aged 20 to 72 years (median age = 69 years). The
vast majority of subjects were not hypertensive (baseline resting systolic/diastolic BP
values, 131.6/80.9 mmHg) (82). With the one static (isometric) training study deleted from
the analysis, a statistically significant reduction of 3.1 mmHg was found for resting diastolic
BP with a trend for a reduction in systolic BP of 3.1 mmHg. Similar and statistically
significant reductions of 2% and 4% also were found for resting systolic and diastolic BP in
an earlier meta-analysis that excluded static training studies (45).
Physical Activity Guidelines Advisory Committee Report G2–20
Part G. Section 2: Cardiorespiratory
Progressive Resistance Exercise and Blood Pressure
For the most recent meta-analysis (82) progressive resistance training took place over a
mean duration of 16.4 weeks, 2 to 3 days per week at 61% of one-repetition maximum. The
mean number of exercises was 10 while the number of sets was 2. Omitting the static study,
the number of repetitions ranged from 8 to 25. Ten of the 12 groups (83%) used exercises
that involved both the upper and lower body. Three of the 9 studies in the meta-analysis
used a circuit training protocol, one used a static protocol, and the remainder used more
conventional types of training protocols. No differences in resting systolic and diastolic BP
were found between traditional and circuit training protocols.
Significance of Exercise-Induced Reductions in Blood Pressure
Although the reductions in BP as a result of aerobic and progressive resistance training may
appear to be small, especially for normotensive and prehypertensive groups, they are
clinically significant. It has been estimated that as little as a 2 mmHg reduction in population
average resting systolic BP can reduce mortality from coronary heart disease, stroke, and all
causes by 4%, 6% and 3%, respectively, while a reduction of 5 mmHg can reduce mortality
risk by 9%, 14%, and 7% (83). The potential numbers of annual lives saved in the United
States as a result of these reductions has been estimated at 11,800 for a 2 mmHg reduction in
resting systolic BP and 27,600 for a 5 mmHg reduction (83).
Question 6. What Is the Relationship Between Physical Activity
and Atherogenic Dyslipidemia?
Conclusion
For the purposes of this review, atherogenic dyslipidemia is defined as the presence of
abnormally low serum concentrations of high-density lipoprotein (HDL) cholesterol and
elevated concentrations of high triglycerides (TG) and small, dense low-density lipoprotein
(LDL) cholesterol. The response of serum lipoproteins to changes in habitual physical
activity have been well studied. In general, both HDL cholesterol and serum TG
reproducibly and favorably respond to changes in habitual physical activity, with increases
in HDL cholesterol and decreases in serum TG, mostly related to the volume of exercise
training and responding with threshold volumes in the range of 7 to 15 miles per week of
regular exercise (equating to an approximate 600 to 800 MET-minutes). Some evidence
indicates that women are less responsive than men to change in habitual exercise, perhaps
due to the observation that those with the largest baseline abnormalities (lower HDL and
higher TG) gain the greatest benefit and men on average have lower HDL and higher TG
than do women. However, when weekly volume or energy expenditure is controlled for men
and women, the sex-related differences seem to be mitigated. Some inconsistent evidence
suggests that LDL cholesterol may respond favorably to exercise training under some
conditions; when it does, it is at the same volume thresholds as observed for HDL and TG.
Finally, more recent studies have observed that fractionated serum lipoproteins respond
Physical Activity Guidelines Advisory Committee Report G2–21
Part G. Section 2: Cardiorespiratory
favorably to aerobic exercise training in a dose-response fashion that is related to the weekly
volume of exercise.
Rationale
A large volume of information is available on the exercise responsiveness of serum
lipoproteins and dose-response effects, much of it accumulated before the 1996 Surgeon
General’s Report. For this review of the literature regarding the relation between habitual
exercise and serum lipoproteins, we have relied mostly upon meta-analyses and reviews
assembled since 1996. The relevant information is well summarized in 2 relatively recent
reviews from Durstine and colleagues (84) and Leon and Sanchez (85). Most of the
information before 1996 is based upon responses in total cholesterol and fractionated lipids
(i.e., HDL, LDL, and TG). Recently some new information has emerged on the response of
lipoprotein sub-fractions to exercise training (86;87).
The response of HDL cholesterol to exercise training traditionally has been well studied. As
illustrated in a recent meta-analysis of exercise-induced effects on HDL cholesterol (88), the
volume of exercise exposure is the primary determinant of exercise-induced modulations of
HDL at a EE threshold of 10 to 12 MET-hours per week. Thus, although some evidence
exists that exercise intensity may be related to HDL increasing as a result of exercise, this
effect becomes insignificant when total exercise volume is controlled.
Women seem to be more resistant to modulation of TG through exercise interventions than
are men, although this is not a consistent finding. In some studies, TG appear to be more
responsive to lower volumes of exercise training than the volumes to which HDL is
responsive, mimicking the responses in insulin action to which TG levels are closely tied
(87). However, the sum of the literature seems to indicate that triglycerides are consistently,
reproducibly and robustly responsive to exercise training of volumes that are comparable to
those that induce changes in HDL (10 to 20 MET-hours per week) and that moderateintensity exercise results in more sustained changes in TG than does high-intensity exercise
once the training stimulus is removed (87).
LDL cholesterol is generally found not to be responsive to exercise training interventions.
However, in the few circumstances when LDL has been observed to be modulated by
exercise, it requires approximately 12 MET-hours per week of exercise to favorably
influence LDL. Recently, studies of the modulation of fractionated lipoproteins with
exercise training have shown that HDL, TG, and LDL size and number are favorably
modulated in a dose-response fashion to exercise training related to training volume and that
800 MET-minutes of exercise per week was required for an effect different from that of a
sedentary control group, whose LDL parameters tended to worsen over time in the absence
of other lifestyle changes (87). More work is needed to understand the magnitude,
consistency, and mechanism of these effects.
Physical Activity Guidelines Advisory Committee Report G2–22
Part G. Section 2: Cardiorespiratory
Question 7: What Is the Relationship Between Physical Activity
and Vascular Health?
Conclusion
Habitual aerobic exercise appears to induce favorable responses in measures of vascular
health. Exercise training initially increases brachial artery flow-mediated dilation
(BAFMD—a measure of endothelial vascular health) with later normalization of BAFMD as
vessels become structurally larger. Habitual aerobic exercise appears to slow the progression
of age-related central arterial stiffening in healthy subjects. Increased levels of habitual
physical activity are associated with slowed progression of carotid intimal medial thickening
(CIMT) in cross-sectional and prospective cohort studies. No significant dose-response data
are available for any of these measures.
Rationale
This section summarizes the effects of chronic aerobic exercise training on measures of
vascular health, including BAFMD, arterial stiffness, and CIMT.
Brachial Artery Flow-Mediated Dilation
Dysfunction of endothelial cells is an early event in the process of atherosclerosis (89), and
is associated with risk factors for cardiovascular disease (90-92). These relations have led to
the use of endothelium-mediated vascular responsiveness as a surrogate biomarker of
vascular health. Brachial artery flow-mediated dilation, a non-invasive measure of
endothelial function, has been shown to correlate with measures of coronary artery function
(93;94) and independently predicts cardiovascular events in patients with established disease
(95-100). Due to its non-invasive nature and relative ease of use, BAFMD has become
increasingly used as a research tool to monitor the efficacy of interventions on vascular
health.
This section provides a review of the current published data on the effects of exercise
training as the primary intervention on BAFMD. A total of 300 abstracts were initially
retrieved and reduced to 22 separate intervention groups (57;99;101-119). All data included
were from RCTs with a minimum exercise training intervention of at least 1 week and
BAFMD data reported at both pre- and post-exercise training. Studies include data from
both apparently healthy subjects as well as those with chronic heart failure, obesity,
dyslipidemia, coronary heart disease, metabolic syndrome, uncomplicated myocardial
infarction, heart transplant, and diabetes.
The results from this literature review provide convincing evidence that exercise training
produces significant changes in the vascular health biomarker BAFMD. Figure G2-2
graphically illustrates the effect sizes seen in all intervention groups. Fifteen of the
Physical Activity Guidelines Advisory Committee Report G2–23
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–24
Figure G2.2. Effect Sizes Seen in Interventions in Which BAFMD Is Used as a
Vascular Health Biomarker
-3.5-3-2.5-2-1.5-1-0.500.511.522.533.5
Watts et al. (2004) (115)
Watts et al. (2004) (114)
Walsh et al. (2003) (108)
Walsh et al. (2003) (109)
Walsh et al. (2003) (108)
Vona et al. (2004) (113)
Rakobowchuk et al. (2005) (119)
Moriguchi et al. (2005) (118)
Maiorana et al. (2001) (103)
Lavrencic et al. (2000) (102)
Kobayashi et al. (2003) (107)
Kelly et al. (2004) (112)
Hamdy et al. (2003) (106)
Guazzi et al. (2004) (111)
Gokce et al. (2002) (99)
Fuchsjager et al. (2002) (104)
Edwards et al. (2004) (110)
Clarkson (1999) (101)
Brendle et al. (2001) (57)
Blumenthal et al. (2005) (117)
Belardinelli et al. (2005) (116)
Allen et al. (2003) (105)
Standardized Effect Size
Figure developed from Clark O; Djulbegovic B. Forest plots in Excel software (data sheet). 2001. Available at
www.evidencias.com.
Part G. Section 2: Cardiorespiratory
Figure G2.2. Data Points
Upper
Limit of the
Confidance
Interval
Lower
Limit of the
Confidance
Interval
Point
Estimate Studies
1.96 0.36 1.16 Allen et al. (2003) (105)
3.18 1.82 2.5 Belardinelli et al. (2005) (116)
0.69 -0.14 0.27 Blumenthal et al. (2005) (117)
1.42 0.35 0.88 Brendle et al. (2001) (57)
1.15 0.27 0.71 Clarkson (1999) (101)
2.7 0.56 1.63 Edwards et al. (2004) (110)
1.44 -0.25 0.6 Fuchsjager et al. (2002) (104)
1.04 -0.09 0.47 Gokce et al. (2002) (99)
3.38 1.52 2.45 Guazzi et al. (2004) (111)
1.52 0.52 1.02 Hamdy et al. (2003) (106)
1.94 0.08 1.01 Kelly et al. (2004) (112)
0.72 -0.76 -0.02 Kobayashi et al. (2003) (107)
2.12 0.51 1.31 Lavrencic et al. (2000) (102)
2.42 0.88 1.65 Maiorana et al. (2001) (103)
2.23 0.46 1.35 Moriguchi et al. (2005) (118)
0.48 -0.26 0.11 Rakobowchuk et al. (2005) (119)
1.78 0.6 1.19 Vona et al. (2004) (113)
0.71 -0.47 0.12 Walsh et al. (2003) (108)
1.86 0.28 1.07 Walsh et al. (2003) (109)
1.68 0.23 0.96 Walsh et al. (2003) (108)
1.08 -0.04 0.52 Watts et al. (2004) (114)
1.43 0.36 0.89 Watts et al. (2004) (115)
Physical Activity Guidelines Advisory Committee Report G2–25
Part G. Section 2: Cardiorespiratory
22 intervention groups included in the analysis showed a statistically significant
improvement in BAFMD (confidence intervals did not contain zero) in response to exercise
training. Of the remaining 7 studies, only one produced a negative effect size (107).
Several factors modulate the magnitude of exercise-induced responses in BAFMD. The
most influential of these appears to be health status before the exercise training intervention.
That is, the magnitude of BAFMD improvement following training is, in part, a function of
the initial or pre-training level. Subjects with cardiovascular disease exhibit greater
improvements in BAFMD following exercise training but start with a lower pre-training
BAFMD. Apparently healthy subjects also show improvement in BAFMD but not to the
same degree as those with cardiovascular disease. The data on apparently healthy subjects
come from only 3 studies and so should be interpreted with some caution (101;105;119).
Interestingly, age does not appear to influence the magnitude of BAFMD response,
suggesting it is modifiable in both young and old.
A second important moderator of response is the type of exercise performed. Changes in
BAFMD were noted in most studies regardless of modality. However, the greatest affect
was seen in those studies using aerobic exercise alone (14 studies) or in combination with
resistance training (6 studies). The evidence for resistance training alone (2 studies) are less
convincing, suggesting resistance training by itself may not be as effective in improving
BAFMD.
A third moderator of response is length of the training period. Shorter periods of exercise
training (8 weeks or less) result in larger changes in BAFMD compared to longer periods of
training (more than 8 weeks). This implies that changes in BAFMD occur rapidly after
initiating training but may diminish with time. This is consistent with the theory that
vascular responses to aerobic exercise training consist of a series of stress-responseadaptation responses, where exercise is the stressor, increased BAFMD is the initial
response, and structural vessel enlargement is the eventual adaptation (with subsequent
normalization of the BAFMD response) (120).
As noted, the modality-specific (aerobic versus resistance) exercise training responses
requires further study. Similarly, the dose-response effects of aerobic exercise training are
notably understudied.
Carotid Intimal-Medial Thickening
Most studies on this outcome are prospective or case-control observational studies.
Relatively few studies have examined the effects of exercise training on CIMT or
progression. From 7 available cross-sectional studies, 4 report lower CIMT in subjects with
higher physical activity levels (121;122) or higher VO2peak (123;124). The remaining 3
studies found no difference between active and sedentary groups (125-127). The
discrepancies between these study results could be related to differences in age and health of
participants, methods of activity measurement and reporting, concomitant lifestyle changes,
length of measurement, and differences in the techniques used to quantify CIMT.
Physical Activity Guidelines Advisory Committee Report G2–26
Part G. Section 2: Cardiorespiratory
The results from interventional studies make it even more difficult to draw definitive
conclusions. From 8 available studies (127-134), only 3 appear to have reported the effects
of exercise training isolated from other concurrent treatments (127;130;132) and none of
these showed significant effects (135). Unfortunately, 2 of these studies were underpowered
to detect CIMT progression, and the third was a pharmaceutical trial where exercise served
as a control and no changes were observed after 4 years (132).
A lack of adequately powered exercise interventional studies is understandable if one
considers the small size of the pooled annual rates of changes in CIMT progression that
occur among control groups from randomized placebo-controlled trials. For studies using
multiple IMT measures from several interrogation angles and carotid segments, the mean
maximum progression rate was 0.0176 millimeters per year with a median SD of 0.05 (136).
Given that sample size calculations rely heavily on rates of change, precision of the
measurement, and projected effectiveness of the intervention, the subject numbers required
and length of exercise training assessment period would have to be much longer than is
traditional in such studies. For example, for a 30% treatment effect, average change in
mean-max CIMT of 0.0352 ± 0.05 millimeters over 2 years, and using as two-tailed alpha,
one would need 468 subjects in each arm of the trial to have 90% power.
Arterial Stiffness
Central arterial stiffening occurs with aging (137) but is often both a consequence and
mechanism of atherosclerotic vasculopathy. The investigation of arterial stiffness has
increased in recent years due to the development of noninvasive assessment techniques
(138-140). However, there appears to be a lack of consensus regarding the most accurate
and reliable method to measure arterial stiffness, complicating the determination of the
efficacy of exercise training responses. The most frequently reported assessment
methodologies are pulse wave velocity, pulse wave analysis, and distensibility/compliance
(change in diameter/change in pressure).
Using these outcome measures, habitual aerobic exercise appears to slow the progression of
age-related central arterial stiffening in healthy subjects as reported in several crosssectional studies (137;141-143). Furthermore, 4 training intervention studies report
significant improvements in measures of central stiffness across sex and age ranges
(141-144). Interestingly, the benefits in central elastic arteries were not replicated in
peripheral muscular arteries (142;145), suggesting that training-specific responses, or
different mechanisms are active in different arterial beds.
The benefits of short-term aerobic exercise training on central stiffness in patient
populations are less clear. One study reported a decrease in aortic pulse wave reflection in
chronic hemodialysis patients following 3 months of aerobic training. This measure returned
to pre-training levels 1 month after training ceased (detraining) (146). Another showed
favorable changes in coronary artery disease subjects within 12 weeks (110), although other
studies reported no effects of training in hypertensive (147;148) or diabetic (149) subjects.
Physical Activity Guidelines Advisory Committee Report G2–27
Part G. Section 2: Cardiorespiratory
Finally, the effects of resistance training on central arterial stiffness are conflicting. Two
cross-sectional studies report a decrease in central but not peripheral arterial compliance in
comparison to sedentary controls (143;150). In contrast, of 4 available case controlled
interventional studies, 2 report increases in measures of central arterial stiffness (151;152)
and 2 report no significant effect (153;154). These differences appear to be related to
intensity, with higher training intensities eliciting higher central stiffness values. Clearly,
large-scale prospective studies are warranted to clarify these discrepancies and to further
elucidate the possible mechanisms involved in the observed changes.
Question 8: What Is the Relationship Between Physical Activity
and Cardiorespiratory Fitness?
Conclusion
Cardiorespiratory fitness is a sensitive and useful measure of changes in response to physical
activity. It demonstrates dose-response relations with overall exercise volume and also with
each of the various components of exercise volume (intensity, frequency, duration, and
longevity). It appears that one can acquire improvements in cardiorespiratory fitness in bouts
as small as 10 minutes each, while holding volume constant. It is unclear whether there is a
relation between the duration of exercise bouts and fitness responses, when total volume is
held constant, especially for vigorous intensity exercise. Changes in fitness during exercise
interventions correspond with changes in cardiovascular risk, but do not always correspond
with changes in cardiovascular risk factors.
Rationale
Cardiorespiratory fitness, as measured by a number of relatively simple and inexpensive
clinical maneuvers, provides strong and independent prognostic information about overall
morbidity and mortality. This relationship extends to men, women, and adolescents. It is
valid in apparently healthy individuals; in patients with a broad range of maladies, including
several types of cancer and cardiovascular disease; and in at-risk individuals with type 2
diabetes, metabolic syndrome, and hypertension (1;155;156). Fitness is also a marker for
functional capacity and ability to perform activities of daily living, especially in older
individuals. Finally, it is used as an outcome measure of adherence and physical activity
exposure in intervention studies. For example, men who improve their fitness (as assessed
by exercise duration) improve their cardiovascular risk. In one report, long-term
cardiovascular risk decreased by 8% for every minute increase in exercise capacity (157).
Due to the correlation between fitness and health status, the responsiveness to changes in
physical activity, and its usefulness as a marker of physical activity levels, cardiorespiratory
fitness is an important health outcome measure in and of itself and is often quoted as an
outcome in health-related physical activity studies. That said, favorable changes in fitness do
not always correspond to change in health outcomes in response to exercise
recommendations (158). The data for this section was acquired from an independent
literature search of the PubMed database using “cardiorespiratory fitness” as a search term
Physical Activity Guidelines Advisory Committee Report G2–28
Part G. Section 2: Cardiorespiratory
and identifying meta-analyses and review articles from both the 1996 date to the present and
before 1996.
Cardiovascular fitness, as measured by any one of a number of parameters associated with
exercise testing (peak VO2, resting heart rate, lactate level or heart rate at submaximal
exercise level, VO2 at ventilatory threshold, time to exhaustion, and others) is extremely
sensitive to changes in physical activity levels and habitual exercise. This is often referred to
as a training effect. The training effect shows a strong dose-response relation to changes in
exercise pattern of various types. Changes in fitness are dependent upon the frequency,
duration, and intensity of exercise bouts and are also dependent upon the longevity of the
exercise training program or intervention (reviewed in 3). The product of exercise
frequency, bout duration, and intensity over time is often referred to as exercise volume and
is proportional to exercise-related energy expenditure. A rich literature exists about the
specific relation between the characteristics of exercise exposure and changes in
cardiorespiratory fitness in the short and long term (3;4;159;160) in individuals of all ages,
including older men and women (161-163). An example of the changes in cardiorespiratory
fitness with training programs of various intensities and amounts (volumes) is demonstrated
in Figure G2-3 (164). As shown, effects on cardiorespiratory fitness of exercise occur both
with increasing intensity at the same volume, and increasing volume at the same intensity.
The groups are clearly distinguishable by differences in group mean differences over time.
However, it is also clear that baseline fitness and the ability to respond to an exercise
intervention have numerous inputs other than physical activity pattern, one of which is
genetic (165). Using the same study population as in the previous figure, when individual
responses to training stimuli are displayed as individual data points ordered by magnitude of
response, it is apparent that the identical stimulus can result in a broad range of responses,
from negative to positive (Figure G2-4). That is, even a strong stimulus (high-volume, highintensity exercise) can result in no significant improvement or even deterioration in
cardiorespiratory fitness in some individuals, while resulting in a large magnitude of change,
much larger than the group mean, in others. This observation has implications for the
construction of physical activity recommendations, depending on whether the goal is to
significantly move the population mean (e.g., 50%) or to affect a significant response in the
vast majority of individuals, in which case a more robust exposure may be required.
As previously noted, changes in cardiorespiratory fitness in response to an exercise
intervention depend upon a number of parameters, including the characteristics of the
exercise stimulus, baseline fitness, sex, age, body mass index, and others. In addition, health
benefits that accrue with an exercise program are often, but not always, correlated with
changes in fitness (160). Two recent studies illustrate the dose-response relations between
exercise exposure and fitness, as well as to several seminal cardiovascular risk markers. The
results from the DREW (166) and STRRIDE (158;164) studies are summarized in
Table G2-2. Cardiorespiratory fitness (peak VO2) can be expressed in absolute terms (liters
of oxygen consumption per minute) or relative to body mass (ml/kg/min). Exercise exposure
in volume can be expressed as energy expenditure or as multiples of resting oxygen
consumption (METs), times duration (e.g., MET-hour), where 1 MET approximately equals
3.5 ml/kg/min).
Physical Activity Guidelines Advisory Committee Report G2–29
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–30
Figure G2.3. Changes in Peak VO2 by Exercise Group
0
5
10
15
20
Pe rc en t C
ha ng e Pe ak V
O
2
Exercise Training Group (volume & intensity)
Inactive Low Volume
Moderate
Low Volume
Vigorous
High Volume
Vigorous
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–31
Figure G2.4. Changes in Peak VO2 by Exercise Group and Ordered by Change
Mild Peak Control Peak
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59
Ordered by ChangeOrdered by Change
Moderate Change Peak High Peak VO 2High Peak VO2
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Ordered by Change Ordered by Change
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–32
Figure G2.4. Data Points
Control Peak
RVO2_1 RVO2_2 Diff 2-1 1-DX
26.88 21.22 0.79 -0.21
28.7 22.67 0.79 -0.21
24.55 20.13 0.82 -0.18
27.9 23.62 0.85 -0.15
23.8 20.2 0.85 -0.15
31.5 26.9 0.85 -0.15
29.55 25.4 0.86 -0.14
25.71 22.2 0.86 -0.14
35 30.4 0.87 -0.13
39.7 34.6 0.87 -0.13
29.4 26.6 0.90 -0.10
29.27 26.52 0.91 -0.09
25.3 23 0.91 -0.09
30.85 28.08 0.91 -0.09
20.4 18.6 0.91 -0.09
20.5 19.1 0.93 -0.07
42.4 39.6 0.93 -0.07
21.9 20.5 0.94 -0.06
32.39 30.44 0.94 -0.06
35.3 33.3 0.94 -0.06
28.1 26.6 0.95 -0.05
29.3 27.8 0.95 -0.05
37.77 35.9 0.95 -0.05
25.1 23.97 0.95 -0.05
RVO2_1 RVO2_2 Diff 2-1 1-DX
27.6 26.5 0.96 -0.04
27.2 26.2 0.96 -0.04
21.4 20.7 0.97 -0.03
15.17 14.73 0.97 -0.03
36 35 0.97 -0.03
22.8 22.2 0.97 -0.03
30.69 30 0.98 -0.02
33.7 33.1 0.98 -0.02
28.5 28 0.98 -0.02
26.8 26.4 0.99 -0.01
33.5 33.4 1.00 0.00
34.9 34.8 1.00 0.00
21.6 21.6 1.00 0.00
26.5 26.5 1.00 0.00
27 27 1.00 0.00
26 26.1 1.00 0.00
37.3 37.8 1.01 0.01
21 21.5 1.02 0.02
29.4 30.1 1.02 0.02
18.7 19.4 1.04 0.04
17.9 18.7 1.04 0.04
34.98 36.57 1.05 0.05
21.3 22.3 1.05 0.05
21.3 22.3 1.05 0.05
RVO2_1 RVO2_2 Diff 2-1 1-DX
24.4 25.8 1.06 0.06
23.1 24.7 1.07 0.07
30.4 32.7 1.08 0.08
17.57 19.23 1.09 0.09
25.3 28 1.11 0.11
21 23.9 1.14 0.14
24.1 27.6 1.15 0.15
25.8 29.9 1.16 0.16
19.81 23.27 1.17 0.17
18.1 21.7 1.20 0.20
22.4 26.9 1.20 0.20
27.9
21.4
33.8
22.5
22.7
23.5
28.6
19.1
33.6
32.75
28.7
33.43
19.2
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–33
Figure G2.4. Data Points (continued)
Mild Peak
RVO2_1 RVO2_2 Diff 2-1 1-DX
23.9667 20.4667 0.85 -0.15
24.3333 21.7667 0.89 -0.11
30.6 29.2 0.95 -0.05
43 41.2 0.96 -0.04
20.5667 19.8667 0.97 -0.03
33.2966 32.1774 0.97 -0.03
29.6 29.1 0.98 -0.02
26.3 25.9 0.98 -0.02
22.1 21.8 0.99 -0.01
32.5 32.1 0.99 -0.01
21.3067 21.1 0.99 -0.01
26.4 26.3 1.00 0.00
23.8 23.9 1.00 0.00
18.1 18.2 1.01 0.01
24.8 25.1 1.01 0.01
27.6 28.1 1.02 0.02
24 24.5 1.02 0.02
42.5 43.6 1.03 0.03
22.2 22.8 1.03 0.03
31.3 32.2 1.03 0.03
24.815 25.5333 1.03 0.03
21.7 22.5 1.04 0.04
33.5 34.8 1.04 0.04
27.6 28.7 1.04 0.04
23.8833 24.8667 1.04 0.04
21.3 22.2 1.04 0.04
30.6 32.1 1.05 0.05
35.7 37.5 1.05 0.05
24.6 25.9 1.05 0.05
RVO2_1 RVO2_2 Diff 2-1 1-DX
29.3 30.9 1.05 0.05
21.2 22.4 1.06 0.06
26.5 28.1 1.06 0.06
26.1 27.8 1.07 0.07
35 37.3 1.07 0.07
28.5 30.4 1.07 0.07
21.5907 23.0738 1.07 0.07
22.5 24.1 1.07 0.07
30.3 32.5 1.07 0.07
24.6 26.4 1.07 0.07
33.4 36.2 1.08 0.08
38.4 41.7 1.09 0.09
26.4373 28.7136 1.09 0.09
21.9033 23.9333 1.09 0.09
18 19.8 1.10 0.10
29.4755 32.803 1.11 0.11
31.4 35.1 1.12 0.12
19.5 21.8 1.12 0.12
24.1 27.2 1.13 0.13
17.84 20.3333 1.14 0.14
33.2833 38 1.14 0.14
26.5213 30.2995 1.14 0.14
20.1333 23.2 1.15 0.15
39.1 45.8 1.17 0.17
21.5 26.1 1.21 0.21
30 36.9 1.23 0.23
19.3667 24.8 1.28 0.28
24.6 32.4 1.32 0.32
22.023 29.503 1.34 0.34
RVO2_1 RVO2_2 Diff 2-1 1-DX
22.8 30.9 1.36 0.36
17.7
19.7
24
29.8
21.3
26.9
22.3
20.2
24.3
27.9
26
28
20.8
32.1
27.3
26.6
26.3
20.5
22
27.2
22.4
23.52
17.94
27.24
27.89
20.22
33.6
27.33
22.35
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–34
Figure G2.4. Data Points (continued)
Moderate Change Peak
RVO2_1 RVO2_2 Diff 2-1 1-DX
28.3712 23.6123 0.83 -0.17
29.3333 28.6 0.98 -0.02
23.8 23.4 0.98 -0.02
26.8 26.7 1.00 0.00
35.7 35.6 1.00 0.00
21.5 21.7 1.01 0.01
26.7667 27.0333 1.01 0.01
37.2 37.8 1.02 0.02
36.3 36.9 1.02 0.02
39.3 40 1.02 0.02
39.7 40.8 1.03 0.03
32.4 33.3 1.03 0.03
35.1 36.4 1.04 0.04
20.7 21.5 1.04 0.04
25 26 1.04 0.04
33.188 34.5905 1.04 0.04
27 28.2 1.04 0.04
27.7 29 1.05 0.05
33.3 35 1.05 0.05
36.4 38.3 1.05 0.05
32.5 34.3 1.06 0.06
31.4333 33.2333 1.06 0.06
39.6 42 1.06 0.06
35.1 37.3 1.06 0.06
34.4 36.7 1.07 0.07
34.4 36.8 1.07 0.07
31.7 34 1.07 0.07
24.4 26.2 1.07 0.07
38.3 41.3 1.08 0.08
20.7 22.4 1.08 0.08
RVO2_1 RVO2_2 Diff 2-1 1-DX
35.5 38.5 1.08 0.08
24 26.2 1.09 0.09
23.7 25.9 1.09 0.09
25.0233 27.5 1.10 0.10
26.1 28.8 1.10 0.10
25.4 28.1 1.11 0.11
33.1 36.9 1.11 0.11
31.2 35 1.12 0.12
28.6 32.1 1.12 0.12
30.2 34.2 1.13 0.13
34.0955 38.633 1.13 0.13
23.1 26.2 1.13 0.13
19.3 21.9 1.13 0.13
37.1 42.1 1.13 0.13
24.4 28.2 1.16 0.16
32.8 38 1.16 0.16
22.1533 25.7333 1.16 0.16
36.5 42.5 1.16 0.16
34 39.7 1.17 0.17
26.2 30.7 1.17 0.17
24 28.6 1.19 0.19
20.2 24.1 1.19 0.19
23.8 28.7 1.21 0.21
25.378 30.603 1.21 0.21
34.9 42.3 1.21 0.21
17.5 21.3 1.22 0.22
26.4 32.2 1.22 0.22
21.3 26.1 1.23 0.23
34.8 42.7 1.23 0.23
28 35.5 1.27 0.27
RVO2_1 RVO2_2 Diff 2-1 1-DX
31.9 41 1.29 0.29
30.4 39.1 1.29 0.29
27.2 35.1 1.29 0.29
35.9016 46.5667 1.30 0.30
25.8 33.5 1.30 0.30
19.64 27.1667 1.38 0.38
17.8155 31.978 1.79
21
23.1
22.8
20.5
19.3
22.9
31.3
28.4
23.9
22.7
17.3
38.4
37.5
41.8
37
23
26.1
39.9
33.1
24.3
22.3
26
21.9
RVO2_1 RVO2_2 Diff 2-1 1-DX
24.7
35.4
24.3
32.9
24.1
25
37.8
37.4
36.2
27.2
26.1
26.6
22.3
20.7
21
27.4
23.9
21.8
37.16
26.8
23.73
22.9
34.9
15.8
31.8
26.04
12.2
17.81
21.56
18.01
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–35
Figure G2.4. Data Points (continued)
High Peak VO2
RVO2_1 RVO2_2 Diff 2-1 1-DX
31.2714 29.8931 0.96 -0.04
24.2333 24.24 1.00 0.00
24.7 25.2 1.02 0.02
38.5 39.8 1.03 0.03
30.69 31.7367 1.03 0.03
29.6 30.8 1.04 0.04
36.9 39.2 1.06 0.06
35.3 37.6 1.07 0.07
31.6 33.7 1.07 0.07
34.1965 36.8 1.08 0.08
32.75 35.3333 1.08 0.08
26.1 28.2 1.08 0.08
31.7 34.7 1.09 0.09
20.2 22.4 1.11 0.11
25.0167 27.8 1.11 0.11
21.8615 24.3222 1.11 0.11
34.3 38.2 1.11 0.11
29.7643 33.1667 1.11 0.11
27.3 30.5 1.12 0.12
24.5333 27.5333 1.12 0.12
31.5 35.6 1.13 0.13
23.7 26.8 1.13 0.13
30.5 34.55 1.13 0.13
32.4667 36.9 1.14 0.14
27.3 31.2 1.14 0.14
28.3 32.4 1.14 0.14
36.1633 41.5333 1.15 0.15
RVO2_1 RVO2_2 Diff 2-1 1-DX
25.5 29.3 1.15 0.15
22.4267 25.8 1.15 0.15
23.9 27.5 1.15 0.15
21.8 25.1 1.15 0.15
19.933 23.013 1.15 0.15
29.7 34.5 1.16 0.16
31.5 36.6 1.16 0.16
26.5 30.8 1.16 0.16
36.4 42.4 1.16 0.16
30.1 35.2 1.17 0.17
21.8 25.5 1.17 0.17
21.5 25.3 1.18 0.18
29.9 35.3 1.18 0.18
19.4 23 1.19 0.19
34.6 41.1 1.19 0.19
19.5 23.3 1.19 0.19
24.8 29.7 1.20 0.20
32.2 38.8 1.20 0.20
30.8533 37.2 1.21 0.21
20.2 24.4 1.21 0.21
25.3 30.7 1.21 0.21
24.13 29.35 1.22 0.22
32.3 39.4 1.22 0.22
32.3667 39.6333 1.22 0.22
35.9 44.2 1.23 0.23
33.3 41.1 1.23 0.23
30.6 37.9 1.24 0.24
RVO2_1 RVO2_2 Diff 2-1 1-DX
21.3 26.4 1.24 0.24
31.4 39.2 1.25 0.25
20.2355 25.323 1.25 0.25
30.3 38.1 1.26 0.26
34.2 43.4 1.27 0.27
23.5 30 1.28 0.28
25.158 32.6655 1.30 0.30
33.3 43.3 1.30 0.30
26.3 35.1 1.33 0.33
29.5 39.8 1.35 0.35
29.9333 41.2 1.38 0.38
30.4357 42.2 1.39 0.39
33.2 46.2 1.39 0.39
22 30.7 1.40 0.40
28.1 40.6 1.44 0.44
17.1 28.9 1.69 0.69
14.5
17.8
27.2
21.3
18.3
26.9
25.6
23.9
26.3
32.7
27.8
RVO2_1 RVO2_2 Diff 2-1 1-DX
35
19.1
26.5
16.8
30.6
37.3
18.8
30.9
30.5
27.9
27.3
21.6
20.9
23.9
23.7
38.63
25.33
21.34
27.12
13.95
23.39
26
27.16
26.89
18.79
22.6667
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–36
Table G2.2. Table of Baseline Characteristics, Exercise Prescriptions, Training Programs, and Outcome Measures in Two
Randomized Controlled Aerobic Exercise Training Studies
Women: DREW (N~120) *
Group
Prescriptions
Training
Volume
(kcal/kg/wk)
Group
Prescriptions
Training
Intensity
(Percent Peak
VO2)
Baseline
Peak VO2
(mL/kg/min)
Training
Program
Training
Prescription
(MET-hr/wk)
Training
Program
Training
Prescription
(MET-
min/wk)
Training
Program
Training
METs
Training
Program
Training
Minutes
per
Week
Change
in Peak
VO2
Outcomes
Change in
Relative
Peak VO2
(mL/kg/min)
Outcomes
Change in
Peak VO2
(METs)
Outcomes
Change in
Body
Mass
Index
Outcomes
Change in
Waist
Circumference
Outcomes
Change in
Blood
Pressure
Outcomes
Change
in Blood
Blood
Lipids
Outcomes
Change in
FBG/ISI
4.0 50% 15.5 3.8 229 2.2 72 4.5% 0.70 0.20 NS Decrease NS NS NS
8.0 50% 14.9 7.6 457 2.2 136 7.0% 1.04 0.30 NS Decrease NS NS NS
12.0 50% 16.0 11.4 685 2.3 192 8.5% 1.36 0.39 NS Decrease Decr. SBP NS NS
Women: STRRIDE (N~30) †
Group
Prescriptions
Training
Volume
(kcal/kg/wk)
Group
Prescriptions
Training
Intensity
(Percent Peak
VO2)
Baseline
Peak VO2
(mL/kg/min)
Training
Program
Training
Prescription
(MET-hr/wk)
Training
Program
Training
Prescription
(MET-
min/wk)
Training
Program
Training
METs
Training
Program
Training
Minutes
per
Week
Change
in Peak
VO2
Outcomes
Change in
Relative
Peak VO2
(mL/kg/min)
Outcomes
Change in
Peak VO2
(METs)
Outcomes
Change in
Body
Mass
Index
Outcomes
Change in
Waist
Circumference
Outcomes
Change in
Blood
Pressure
Outcomes
Change
in Blood
Blood
Lipids
Outcomes
Change in
FBG/ISI
14.0 50% 23.4 13.3 800 3.3 193 6.5% 1.52 0.43 NS NS NS Decr. TG Lg. Incr. ISI
14.0 75% 23.9 13.3 800 5.1 134 14.3% 3.42 0.98 NS NS NS NS Incr. ISI
23.0 75% 24.1 21.9 1,314 5.2 195 16.4% 3.95 1.13 Decrease Decrease NS NS Incr. ISI
Men: STRRIDE (N~30) †
Group
Prescriptions
Training
Volume
(kcal/kg/wk)
Group
Prescriptions
Training
Intensity
(Percent Peak
VO2)
Baseline
Peak VO2
(mL/kg/min)
Training
Program
Training
Prescription
(MET-hr/wk)
Training
Program
Training
Prescription
(MET-
min/wk)
Training
Program
Training
METs
Training
Program
Training
Minutes
per
Week
Change
in Peak
VO2
Outcomes
Change in
Relative
Peak VO2
(mL/kg/min)
Outcomes
Change in
Peak VO2
(METs)
Outcomes
Change in
Body
Mass
Index
Outcomes
Change in
Waist
Circumference
Outcomes
Change in
Blood
Pressure
Outcomes
Change
in Blood
Blood
Lipids
Outcomes
Change in
FBG/ISI
14.0 50% 30.0 13.3 800 4.3 161 7.4% 2.22 0.63 Decrease Decrease NS Decr. TG Lg. Incr. ISI
14.0 75% 33.6 13.3 800 7.2 99 11.2% 3.76 1.08 NS Decrease NS NS Incr. ISI
23.0 75% 31.0 21.9 1,314 6.6 152 20.0% 6.20 1.77 Decrease Decrease Decr. SBP
Incr. HDL/
Decr. TG Lg. Incr. ISI
Part G. Section 2: Cardiorespiratory
Physical Activity Guidelines Advisory Committee Report G2–37
Table G2.2. Table of Baseline Characteristics, Exercise Prescriptions, Training Programs, and Outcome Measures in Two
Randomized Controlled Aerobic Exercise Training Studies (continued)
Men and Women: STRRIDE (N~60) †
Group
Prescriptions
Training
Volume
(kcal/kg/wk)
Group
Prescriptions
Training
Intensity
(Percent Peak
VO2)
Baseline
Peak VO2
(mL/kg/min)
Training
Program
Training
Prescription
(MET-hr/wk)
Training
Program
Training
Prescription
(MET-
min/wk)
Training
Program
Training
METs
Training
Program
Training
Minutes
per
Week
Change
in Peak
VO2
Outcomes
Change in
Relative
Peak VO2
(mL/kg/min)
Outcomes
Change in
Peak VO2
(METs)
Outcomes
Change in
Body
Mass
Index
Outcomes
Change in
Waist
Circumference
Outcomes
Change in
Blood
Pressure
Outcomes
Change
in Blood
Blood
Lipids
Outcomes
Change in
FBG/ISI
14.0 50% 26.8 13.3 800 3.8 176 7.0% 1.88 0.54 NS Decrease NS Decr. TG Lg. Incr. ISI
14.0 75% 29.1 13.3 800 6.2 116 12.6% 3.67 1.05 NS Decrease NS NS Incr. ISI
23.0 75% 28.2 21.9 1,314 6 170 18.5% 5.22 1.49 Decrease Decrease NS
Incr.
HDL/
Decr. TG Lg. Incr. ISI
* Church, JAMA, 2007 (166)
† Duscha, Chest, 2005 (164); Johnson, Am J Cardiol, 2007 (158)
Decr., decreased; FBG, fasting blood glucose; HDL, high-density lipoprotein cholesterol; Incr., increase; ISI, insulin sensitivity index, a parameter of insulin sensitivity derived from a frequently
sampled glucose tolerance test; lg., large; MET, metabolic equivalent; NS, not significant; SBP, systolic blood pressure; TG, triglycerides.
Part G. Section 2: Cardiorespiratory
Similarly, changes in fitness in response to an exercise intervention can be expressed in
percent change or absolute change. Examples of each of these in the two study populations
are illustrated in this table. Because relative VO2 is normalized to body mass, it is relatively
sensitive to changes in body mass during interventions. The observation that relative fitness
measures (relative peak VO2) at baseline are 50% lower in DREW women than in
STRRIDE women, may be due in part to the higher BMIs of DREW women
(30-40 kg•m-2) than in STRRIDE women (25-30 kg•m-2) and demonstrates the sensitivity of
maximal fitness measures, and exercise prescriptions when expressed as a percentage of
baseline fitness to BMI. However, the difference in body mass between the women in these
two study groups does not completely account for the differences in cardiorespiratory
fitness, as the mean absolute peak VO2 for women in DREW was approximately 1.2 L/min
and 1.8 L/min in STRRIDE women. Similarly, women generally have lower
cardiorespiratory fitness than do men and, therefore, the same relative intensity of exercise
(e.g., 50% peak VO2) represents a lower energy expenditure in women than it does in men.
Relative percent increases in fitness in response to a fixed intervention is highly dependent
on baseline fitness level, although absolute fitness measures are not. Finally, it is apparent
that fitness changes do not correlate with all outcome measures in a monotonic and linear
fashion (e.g., insulin sensitivity). Examination of these two studies in combination seem to
indicate that at least 800 MET-minutes per week of physical activity are required to produce
improvements in health outcomes, irrespective of the relative percent increases in
cardiorespiratory fitness.
Effects of Daily Fractionization (Accumulation) of Exercise Bouts on
Cardiorespiratory Fitness and Cardiovascular Health
Many groups are highly interested in whether multiple short bouts of exercise (e.g., 3 bouts
of 10 minutes) is equivalent to one long bout (e.g., 1 bout of 30 minutes) per day for
improving fitness levels. It should be evident that the choice of interval over which one
integrates and accumulates a physical activity exposure (e.g., day, week, month, or year) is
somewhat artificial, but interest remains in the issue of whether the benefits of activity are
the same when total daily activity is divided over the course of the day. Several
investigators have compared short versus long exercise regimens in an attempt to address
this question (167-179). Data for this section were obtained from a literature search. From
the appendix table (Table G2-A9, which summarizes these studies, can be accessed at
http://www.health.gov/paguidelines/report/), it is apparent that these studies do not provide a
clear answer to effects on cardiorespiratory fitness. Among these 11 studies, a single long
bout of exercise was superior to multiple daily bouts in 3 studies of improving
cardiorespiratory fitness. Multiple, shorter bouts were more effective in 2 studies, no
difference was observed in 5 studies, and 1 study reported no improvement in either single
long or multiple short exercise bouts. A pattern does appear to form within the few welldesigned studies, however. It appears that both single long bouts and multiple shorter bouts
of aerobic exercise training do elicit significant improvements in fitness, and that the
evidence is relatively strong that comparable fitness responses can be achieved with
different fractionization of the volume, given that the daily volume of the exposure is the
same.
Physical Activity Guidelines Advisory Committee Report G2–38
Part G. Section 2: Cardiorespiratory
Several factors likely play a role in the variability of the findings. Careful analysis of
demographics and methods of each study indicate that the populations under study differ
widely, from college students to middle aged and overweight individuals. It is possible that
the more sedentary an individual is at baseline (e.g., the lower the peak VO2), the less a
difference is observed in fitness responses when the exposure is fractionated over the course
of the day. This may be due to the fact that less fit individuals are exercising at lower
absolute intensities (e.g., walking) and that fractionation has less influence on fitness
responses when the intensity of the exercise is lower. If true, then as fitness levels increase,
fitness responses should be more dependent on how the exposure is fractionated. This
concept has not been tested but begs for further work.
Second, these studies differed quite a bit in exercise exposures (e.g., intensity, frequency).
The intervention length ranges from 8 weeks to 18 weeks, while the intensity varies from
50% to 60% of predicted heart rate maximum to 70% to 80% of heart rate reserve. This
variation is reflected in the large range of fitness changes reports, from no change to as
much as 19% improvement. For example, in a study of young college students who trained
at 50% to 60% of predicted heart rate maximum, no improvement in cardiorespiratory
fitness was reported. It is very possible that the exercise exposure was not adequate for this
population. That is, it is possible that one cannot distinguish the differences in responses
between long and short bout activities when the total volume of the stimulus is insufficient
to generate optimal responses—for example, where the total exercise time is fixed at
30 minutes of moderate-intensity activity, and a longer period of moderate-intensity activity
or the same period of vigorous-intensity activity might better distinguish the responses to
bout duration when total exercise volume is held constant. Moreover, although these studies
report their results as fitness gains, not all studies use the same fitness measures. Many of
the studies do not perform a maximal exercise test and only extrapolate a maximal value
based upon a sub-maximal test.
Third, the other outcomes in these studies, cardiovascular risk markers, such as lipids,
glucose control, and others show various responses to the interventions. When responses
differ, the continuous exposure regimens seem to have more favorable outcomes than do
fractionated regimens, although the data are too limited to provide a reliable estimate of the
effects of fractionated exercise on such outcomes.
Overall Summary and Conclusions
The weight of evidence points toward a favorable relation between increases in habitual
dynamic aerobic exercise and cardiovascular health outcomes, including coronary heart
disease morbidity and mortality, stroke, control of blood pressure, atherogenic dyslipidemia,
vascular function measures, and cardiorespiratory fitness. In addition, dynamic aerobic
exercise is considered a standard of therapy for increasing functional performance in
peripheral arterial disease. In many of these outcomes, including cardiovascular morbidity
and mortality, there appears to be a more favorable response with increasing intensity of
exercise bouts, although exercise volume is poorly controlled in some studies and may be
Physical Activity Guidelines Advisory Committee Report G2–39
Part G. Section 2: Cardiorespiratory
the important mediating exercise parameter. Also, the more powerful relation between
exercise intensity and outcomes does not hold for all outcomes in experimental studies,
especially when weekly volume or energy expenditure is held constant (160). In many, if not
most, cardiovascular outcomes, favorable responses are notable and reproducible when the
volume of physical activity exceeds 800 MET-minutes per week. A combination of
endurance exercise bouts with different intensities, durations, and frequencies per day and
week can achieve this level of exercise, which is approximately equivalent to 12 miles per
week of walking or jogging at any intensity. As energy expenditure at a given perceived
intensity is highly dependent upon baseline fitness level, sex, and type of activity, a volume
target can be individualized with adjustment of bout intensity, duration, and frequency, both
initially and as greater fitness levels are achieved. Given that more volume is likely to result
in greater benefits but also higher injury and cardiovascular risk, the ultimate volume goal
should be approached gradually upon the initiation of a program, especially in initially
sedentary individuals.
Research Needs
In the course of reviewing the literature that contributed to the information presented in this
chapter, several significant deficiencies in the published literature became apparent. More
information addressing the following issues would have significantly improved the
information base used to formulate physical activity recommendations. The
Cardiorespiratory Health subcommittee encourages governmental agencies to highlight
research in these areas before the next iteration of the Physical Activity Guidelines for
Americans.
1. What is the time course of acquisition of the cardiovascular health benefits resulting
from increases in habitual physical activity?
2. What are the cardiovascular health benefits of varying exercise bout duration,
frequency, and intensity, while controlling for total volume?
3. What effect does daily exercise exposures accumulated in short bouts have on the
acquired cardiovascular health benefits of habitual physical activity?
4. What are the effects of resistance training on cardiovascular health and what is the
nature of dose-response effects (varying intensity, bout volume, and frequency of
programs)?
5. Are there sex differences in cardiovascular health benefits of habitual exercise when
controlling for volume?
6. What are the specific harmful effects of physical inactivity on cardiovascular health?
7. Are there responses that differ by ethnic and racial minority differences?
Physical Activity Guidelines Advisory Committee Report G2–40
Part G. Section 2: Cardiorespiratory
8. What are the specific effects of aerobic training, resistance training, and a
combination on selected biomarkers of vascular health, such as brachial artery
flow-mediated dilation? What are the dose-response effects?
9. What are the main characteristics of an exercise program for preventing and treating
peripheral artery disease? What are the exercise dose-response patterns, sex
differences, exercise modality options, and differential effects on diabetic patients
with PAD, on asymptomatic patients, and are there biomarkers to predict exercise
responders?
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Physical Activity Guidelines Advisory Committee Report G2–57
171. Woolf-May K, Kearney EM, Owen A, Jones DW, Davison RC, Bird SR. The
efficacy of accumulated short bouts versus single daily bouts of brisk walking in
improving aerobic fitness and blood lipid profiles. Health Educ.Res. 1999
Dec;14(6):803-15.
172. Murphy MH, Nevill AM, Hardman AE. Different patterns of brisk walking are
equally effective in decreasing postprandial lipaemia. Int.J.Obes.Relat Metab Disord.
2000 Oct;24(10):1303-9.
173. Schmidt WD, Biwer CJ, Kalscheuer LK. Effects of long versus short bout exercise on
fitness and weight loss in overweight females. J.Am.Coll.Nutr. 2001 Oct;20(5):494501.
174. Thomas DQ, Lewis HL, McCaw ST, Adams MJ. The effects of continuous and
discontinuous walking on physiologic response in college-age subjects.
J.Strength.Cond.Res. 2001 May;15(2):264-5.
175. Murtagh EM, Boreham CA, Nevill A, Hare LG, Murphy MH. The effects of 60
minutes of brisk walking per week, accumulated in two different patterns, on
cardiovascular risk. Prev.Med. 2005 Jul;41(1):92-7.
176. O'Donovan G, Owen A, Bird SR, Kearney EM, Nevill AM, Jones DW, Woolf-May
K. Changes in cardiorespiratory fitness and coronary heart disease risk factors
following 24 wk of moderate- or high-intensity exercise of equal energy cost.
J.Appl.Physiol 2005 May;98(5):1619-25.
177. Osei-Tutu KB, Campagna PD. The effects of short- vs. long-bout exercise on mood,
VO2max, and percent body fat. Prev.Med. 2005 Jan;40(1):92-8.
178. Macfarlane DJ, Taylor LH, Cuddihy TF. Very short intermittent vs continuous bouts
of activity in sedentary adults. Prev.Med. 2006 Oct;43(4):332-6.
179. Quinn TJ, Klooster JR, Kenefick RW. Two short, daily activity bouts vs. one long
bout: are health and fitness improvements similar over twelve and twenty-four
weeks? J.Strength.Cond.Res. 2006 Feb;20(1):130-5.
Part G. Section 3:
Metabolic Health
Introduction
Metabolic syndrome and diabetes are highly significant public health problems in the United
States. Ford and colleagues (1) estimate, based on government surveys, that 47 million
people in the United States have metabolic syndrome. It is also estimated that 20.8 million
Americans (about 7% of the US population) have type 1 diabetes (T1D) or type 2 diabetes
(T2D), of whom only two thirds have been diagnosed and the remaining one third are
unaware of their condition (2;3). The great majority (estimated to be 90% or more) of these
individuals have T2D. The prevalence of diabetes is higher among persons of Hispanic,
African American, and Native American background than among persons of non-Hispanic
white origins. The majority of deaths in persons with diabetes are caused by cardiovascular
disease (CVD), including myocardial infarction and stroke. People with diabetes not only
have a high prevalence of manifestations of atherosclerosis but also have increased
prevalence of cardiovascular (CV) risk factors, including hypertension and the
dyslipidemias. Alarmingly, type 2 diabetes, once called adult-onset diabetes because it
chiefly presented in middle-aged persons, is now appearing in ever younger people, and its
prevalence in adolescents and children is increasing rapidly. The potential ramifications of
T2D in adolescents and children has yet to be determined.
Exercise and physical activity play a clear role in preventing and treating metabolic
syndrome and T2D as well as the macrovascular complications of T2D. The importance of
the role of exercise and physical activity is highly important and is of increasing interest
both in the United States and in other countries as well, as the magnitude of the public health
problems of metabolic syndrome and diabetes continues to increase and as solutions are
being sought. The role of physical activity and exercise in treating T1D is less well
established than for T2D, although evidence suggests that benefits are likely, perhaps most
of all in the area of reducing mortality, CVD risk factors, and microvascular complications.
For both T1D and T2D, physical activity may prevent the development of diabetic
neuropathy and diabetic nephropathy. Finally, it appears likely that physical activity and
exercise may help prevent and treat gestational diabetes although more research is needed to
further establish these findings.
Physical Activity Guidelines Advisory Committee Report G3–1
Part G. Section 3: Metabolic Health
Review of the Science
Overview of Questions Asked
This chapter considers 6 major questions dealing with the potential role of physical activity
and exercise in preventing and treating metabolic syndrome, T1D and T2D, common
complications of diabetes, and gestational diabetes:
1. Does physical activity have a role in preventing or treating metabolic syndrome?
2. Does physical activity have a role in preventing and treating type 2 diabetes?
3. Does physical activity have a role in reducing macrovascular risks in type 2
diabetes?
4. Does physical activity have benefits for type 1 diabetes?
5. Does physical activity have a role in preventing and treating diabetic microvascular
complications?
6. Does physical activity and exercise have a role in preventing and treating gestational
diabetes?
Data Sources and Process Used To Answer Questions
The Metabolic Health subcommittee used the Physical Activity Guidelines for Americans
Scientific Database as its primary source of references for the topics covered in this section
of the report (see Part F: Scientific Literature Search Methodology, for a full description of
the Database). The Database contains studies published in 1995 and later. In its search, the
subcommittee used broad study selection criteria, which included: all age groups; all study
designs; all physical activity types as well as cardiorespiratory fitness; disease conditions
including T2D, T1D, diabetic nephropathy/neuropathy/retinopathy, metabolic syndrome,
gestational diabetes, hypoglycemia, glucose, and insulin.
Studies were also identified through computerized searches of several databases, including
PubMed, CINAHL, Health Plan, Cochrane Collaboration, and Best Evidence. Standard
MESH terms often were only partially successful in identifying relevant articles. Articles
also were found through a combination of searching published reference lists as well as
references from meta-analyses and systematic reviews.
Physical Activity Guidelines Advisory Committee Report G3–2
Part G. Section 3: Metabolic Health
Question 1. Does Physical Activity Have a Role in Preventing or
Treating Metabolic Syndrome?
Conclusions
Regular physical activity is associated with reduced risk of metabolic syndrome (Tables
G3.A1, G3.A2, G3.A3, and G3.A4, which summarize these studies, can be accessed at
http://www.health.gov/paguidelines/report/.). The available data demonstrate an inverse
dose-response association between level of activity and risk of metabolic syndrome, with the
minimal amount of activity to prevent metabolic syndrome ranging from 120 to 180 minutes
per week of moderate-intensity physical activity, and many studies supporting a goal of 150
minutes per week. The findings derived from studies using self-report measures of physical
activity are similar to those studies in which cardiorespiratory fitness was measured. The
dose-response association between physical activity and prevention of metabolic syndrome
is similar in men and women. Although limited data support the use of exercise for the
treatment of metabolic syndrome, this is an area in great need of more work, as is the role of
physical activity in preventing and treating metabolic syndrome in youth (Table G3.A5,
which summarizes these studies, can be accessed at http://www.health.gov/paguidelines/
report/.) and across ethnicities.
Introduction
A number of clinical criteria, such as those of the National Cholesterol Education Program
and World Health Organization (4), have been developed to define the metabolic syndrome.
These criteria are very similar and share the following cluster of characteristics: abnormal
levels of lipids (low high-density lipoprotein and high triglycerides), elevated glucose,
hypertension, and excess abdominal obesity (5-8). This review is not limited to any specific
clinical definition of metabolic syndrome but rather includes any report in which the
definition of metabolic syndrome was consistent with the above characteristics.
Rationale
In general both cross-sectional and longitudinal cohort studies consistently show a lower
incidence and prevalence, respectively, of metabolic syndrome among physically active
individuals as compared with their inactive peers (9-45).
Dose-Response Relation
In the cross-sectional studies, which examined the prevalence of metabolic syndrome across
levels of physical activity and primarily used questionnaires to obtain self-report data
(Figure G3.1), (Table G3.A.3, which summarizes these studies, can be accessed at
http://www.health.gov/paguidelines/report/.), all found an inverse gradient between amount
of physical activity and metabolic syndrome (10;11;13;21;23;26;36).
Physical Activity Guidelines Advisory Committee Report G3–3
♦ Lakka (13) – Men  Zhu (21) – Men S Zhu (21) – Women
x Ford (1) – Both ¿ Bertrais (23) – Men z Bertrais (23) – Women
… Carrol (10) – Men Δ Irwin (11) – Women  Halldin (36) – Both
O
dd s R
at io o f H
av in g M
et ab ol ic S
yn dr om e 0
0.2
0.4
0.6
0.8
1
1.2
0 100 20 40 60 80
Level of Self Report Physical Activity (%)
Part G. Section 3: Metabolic Health
Figure G3.1. Summary of Cross-Sectional Physical Activity and Metabolic Syndrome
Studies Using Categories of Physical Activity That Could Be Used To
Examine Dose-Response
From the cross-sectional studies in which minutes per week of moderate-intensity physical
activity for each category were provided or could be estimated, 120, 150, and 180 minutes
or more per week of moderate intensity activity have all been reported as minimum amounts
associated with reduced prevalence of metabolic syndrome (13;23;26;36). It should be noted
that these studies used different methods of activity assessment, the activity categories have
large ranges, and the cut-points for the activity categories were not similar or generated
using the same statistical methods. None of the studies was designed or powered to analyze
the minimal dose of activity to prevent metabolic syndrome. However, the cross-sectional
data supports that obtaining at least 120 to 180 minutes per week of moderate-intensity
physical activity is consistently associated with a lower prevalence of metabolic syndrome.
Only the 2002 report from Laaksonen and colleagues (Figure G3.2) provides data that could
be used to examine the dose-response between physical activity and the development of
metabolic syndrome (41).
Physical Activity Guidelines Advisory Committee Report G3–4
1.4
1.2
1
0.8
0.6
0.4
0.2
0
O
R
fo r D
ev el op m en t o
f M
et ab ol ic S
yn dr om e 3 60 or 61-180 >180 1 2
less
Fitness TertilesMinutes of Mod/Vig Leisure
Time Physical Activity
Part G. Section 3: Metabolic Health
Figure G3.2. Data Prospectively Demonstrating That Both Higher Levels of Physical
Activity and Fitness Protect Against the Future Development of
Metabolic Syndrome
Source: Laaksonen et al. (41)
Figure G3.2. Data Points
The results were similar to those from the cross-sectional studies. A dose-response relation
exists between level of activity and risk of developing metabolic syndrome, with 180 or
more minutes per week of moderate intensity physical activity being the minimal amount of
time associated with reduced risk of developing metabolic syndrome.
Development
of Metabolic
Syndrome
Time
Physical
Activity
Low
Time
Physical
Activity
Middle
Time
Physical
Activity
High
Fitness
Tertiles
Low
Fitness
Tertiles
Middle
Fitness
Tertiles
High
Odds Ratio 1 0.66 0.55 1 0.59 0.36
Physical Activity Guidelines Advisory Committee Report G3–5
CARDIA - Both KIHD - Men
ACLS - Men ACLS - Women
1.2
1
0.8
0.6
0.4
0.2
0
0 1 2 3
Tertiles of Fitness
R
is k of D
ev el op in g M
et ab ol ic S
yn dr om e Part G. Section 3: Metabolic Health
Physical Activity Level Versus Cardiorespiratory Fitness
Laaksonen and colleagues also measured cardiorespiratory fitness and, as depicted in
Figure G3.2 and Table G3.A1, the inverse dose-response relationship associated with
prevention of metabolic syndrome, is even stronger than that seen with questionnaireassessed self-report of physical activity (41).
All available prospective studies that measured fitness and categorized participants based on
fitness level similarly show a strong inverse dose-response between fitness and risk of
developing metabolic syndrome (Figure G3.3) (39;41;46-48) .
Figure G3.3. Summary of Longitudinal Fitness and Metabolic Syndrome Studies
That Used Categories of Fitness To Examine Dose-Response Relations
CARDIA, Coronary Artery Risk Development in Young Adults; KIHD, Kuopio Ischemic Heart Disease Risk Factor Study;
ACLS, Aerobic Center Longitudinal Study
Physical Activity Guidelines Advisory Committee Report G3–6
Part G. Section 3: Metabolic Health
Thus, despite the methodological differences in assessing physical activity through selfreport (questionnaire) vs. measured cardiorespiratory fitness, the association with the
prevention of metabolic syndrome is similar for these two modes of activity assessment.
Sex Differences
The available data are composed of men-only studies, women-only studies, and combinedsex studies, with no one type of study comprising the preponderance of the data. As
demonstrated in Figure G3.1, the physical activity-metabolic syndrome association is similar
in men and women, indicating that both men and women benefit from participating in
regular physical activity. As demonstrated in Figure G3.3, the fitness-metabolic syndrome
association also is similar in men and women. Thus, no matter whether studies using selfreports of physical activity or objective measures of fitness, it appears that no sex
differences exist in regard to the benefits of physical activity in preventing metabolic
syndrome.
Youth
Only very limited data are available for youth. These studies, using a variety of methods to
quantify physical activity and define metabolic syndrome, are consistent with the findings in
adults, namely that higher levels of activity and fitness are associated with reduced risk of
metabolic syndrome (Table G3.A5, which summarizes these studies, can be accessed at
http://www.health.gov/paguidelines/report/.) (15;44;49;50;50-53). However, this topic is
deserving of future study and investigation.
Effect of Race and Ethnicity
The majority of studies with large sample sizes were conducted in Europe or were composed
of persons of American or European descent. Though some of the better studies were
conducted in populations composed of both African Americans and whites, no studies have
examined the physical activity-metabolic syndrome association in an African American or
Mexican American population only (11;26;46). Thus, the data on the relationship between
physical activity or fitness in terms of preventing metabolic syndrome in non-white
populations are limited, and this is clearly an area that needs additional research. It should be
noted that in the studies that used study populations composed of both non-Hispanic whites
and African Americans, such as the National Health and Nutrition Examination Survey
(NHANES) and the Coronary Artery Risk Development in Young Adults (CARDIA) Study,
a strong dose-response relation between activity (or fitness) and prevention of metabolic
syndrome was evident (26;46).
Prolonged Sitting and Other Sedentary Behaviors
Although regularly participating in physical activity and not leading a sedentary lifestyle
may appear to be synonymous, evidence suggests that these two behaviors should be treated
as different dimensions of the same pubic health issue. In other words, it is important not
only to obtain adequate amounts of aerobic exercise but also to avoid extreme sedentary
behaviors, such as prolonged sitting. This is obviously of great importance in today’s
Physical Activity Guidelines Advisory Committee Report G3–7
Part G. Section 3: Metabolic Health
environment, in which the typical work day is characterized by long bouts of sitting and
most non-work hours are spent watching television. Available data suggest a direct
relationship between the prevalence of metabolic syndrome and the time spent watching
television or using the computer (23;25;26). For example, using NHANES data (n=1,626
men and women), Ford and colleagues observed that individuals who reported watching
television or using the computer 4 or more hours a day had a 2 times greater risk of having
metabolic syndrome compared to individuals who reported less than 1 hour a day of
television or computer use (26). Given that the current environment in the United States
promotes sedentary behavior both within and outside the work place, strategies for reducing
sedentary behavior, in addition to promoting exercise, have great potential public health
impact.
Role of Physical Activity in Treating Metabolic Syndrome
Numerous studies have examined the benefits of exercise training on individual components
of metabolic syndrome, such as blood pressure or fasting glucose. In general, improvements
to the variables of interest are noted with exercise training. However, no published studies
have been specifically designed to examine the efficacy of exercise training in the reversal
of the clinical diagnosis of metabolic syndrome. Two reports have conducted post-hoc
analyses to examine the role of exercise in reversing metabolic syndrome. Using data from
the HERITAGE study, Katzmarzyk and colleagues report that 20 weeks of aerobic training
were associated with improvements in triglycerides, blood pressure, fasting glucose, and
waist circumference among 105 participants who had metabolic syndrome at baseline (54).
Further, the prevalence of metabolic syndrome decreased 30.5% in this sub-set of
participants who received exercise training. However, this study was not controlled, which
makes the interpretation of this data challenging. In a recent manuscript using data from the
dose-response STTRIDE study, Johnson and colleagues observed an improvement in waist
circumference, triglycerides, and blood pressure when the included exercise groups (walking
or jogging exercise in varying intensities) (n=130) were combined. None of these variables
changed in the control group (n=41) (55). The prevalence of metabolic syndrome also
decreased in the combined exercise group from 41% to 27%, with no change in prevalence
of metabolic syndrome in the control group (39% to 46%). Although these preliminary data
generated from post hoc analyses suggest that exercise training may be an important
therapeutic option for the treatment of metabolic syndrome, this area needs additional
research. In particular, clinical exercise trials prospectively designed and powered to
examine the efficacy of exercise in treating metabolic syndrome are needed.
Resistance Training
Very few studies have examined the role of resistance training or quantified muscular
strength in preventing or treating metabolic syndrome (56-58). In both a cross-sectional and
longitudinal report from the Aerobic Center Longitudinal Database, greater muscular
strength was associated with lower risk of metabolic syndrome (56;57). However, in the
report using longitudinal data, the degree of risk reduction associated with greater levels of
strength was attenuated (from −34% to −24%) when cardiorespiratory fitness was adjusted
Physical Activity Guidelines Advisory Committee Report G3–8
Part G. Section 3: Metabolic Health
for (57). Given the important role of skeletal muscle in insulin sensitivity, developing a
better understanding of the role of resistance training in the prevention and treatment of
metabolic syndrome is an area of great interest.
Question 2. Does Physical Activity Have a Role in Preventing and
Treating Type 2 Diabetes?
Conclusions
Increased levels of physical activity are associated with significantly decreased risks of
developing T2D. Most of the studies addressing T2D prevention have focused on vigorous
activity, but a number have included walking at moderate intensity, which has proven
efficacious as well. Importantly, two randomized controlled trials (RCTs) and results of
observational studies provide empiric evidence to support 150 minutes per week of
moderate intensity physical activity for T2D prevention. Several studies have shown that
30 minutes per day of moderate intensity exercise 5 days per week are effective in
preventing T2D. Available data do not enable minimal recommendations, although some of
the large observational studies show that any amount of increased physical activity is
associated with T2D prevention. Recommendations are valid for both men and women. Data
are insufficient to clearly show that the benefits are uniform across all ethnicities and racial
groups but no data support a lack of benefit and available data do support the benefit in these
groups.
Introduction
As noted at the beginning of this chapter, diabetes is a highly significant public health
problem in the United States. Available data reveal that physical activity has a strong role in
the prevention and treatment of T2D. These data include results from observational studies,
and RCTs as well as physiological studies related to physical activity and/or exercise. The
relationship between T2D and cardiovascular fitness also is important because population
studies reveal a direct correlation between all-cause mortality and reduced fitness in persons
with T2D (59;60). Following are data that support the importance of physical activity and
exercise in the prevention and treatment of T2D as well as a discussion of the safety of
exercise for persons with T2D.
Rationale
Observational Studies of Physical Activity in Preventing Type 2 Diabetes
Large prospective cohort and cross-sectional observational studies that assessed physical
activity through the use of questionnaires all show that increased physical activity levels are
associated with reduced risk for developing T2D. As with the assessments looking at the
relationship between metabolic syndrome and physical activity, it should be noted that these
studies used different methods of activity assessment, the activity categories have large
ranges, and the cut-points for the activity categories were not generated using the same
Physical Activity Guidelines Advisory Committee Report G3–9
Part G. Section 3: Metabolic Health
statistical methods. In addition, none of the studies was designed or powered to analyze the
minimal dose of activity to prevent T2D. Importantly though, however the studies were
conducted, the benefit of physical activity in preventing T2D is consistently present.
Major prospective cohort studies are described here to illustrate the range of methods
used and results obtained. Meta-analyses and structured reviews on this topic are
summarized in Table G3.A6, which summarizes these studies and can be accessed at
http://www.health.gov/paguidelines/report/. These studies reveal that both moderate and
vigorous physical activity can prevent T2D. Dose-response summary information is
provided separately below.
In a study by Helmrich and colleagues (61) in 5,990 male alumni of the University of
Pennsylvania, incidence rates of T2D decreased as energy expenditure in leisure time
physical activity in kilocalories per week increased from less than 500 to 3,500. They found
that for each 500 kilocalorie increment in leisure-time physical activity, the age-adjusted risk
of T2D was reduced by 6% (relative risk [RR]=0.94, 95% CI= 0.90-0.98) (61). In a study by
Manson and colleagues (62) in the Nurses’ Health Study cohort (87,252 US women aged 34
to 59 years), the investigators found that women who engaged in vigorous exercise at least
once per week had an age-adjusted RR of 0.67 when compared to women who did not
exercise (P <0.0001). This significant benefit persisted even after adjustment for body mass
index (BMI) although results were somewhat attenuated by this measure (62). Hu and
colleagues (63) compared the benefits of walking with benefits of vigorous physical activity
on risk of developing T2D in the Nurses’ Health Study. Physical activity was divided into
quintiles in this study. The authors found that walking (considered a moderate intensity form
of exercise) as well as vigorous activity were associated with decreased risk of T2D, with
greater physical activity levels providing the most benefit. A study of 5,159 British men
revealed a decreased risk for developing T2D that progressively decreased with increasing
levels of physical activity (64). Participants were sorted into one of 6 defined levels of
physical activity ranging from inactive to vigorously active based on frequency and intensity
of the physical activities of each participant. The authors found that the age-adjusted relative
risk of T2D decreased progressively with increasing levels of physical activity with even
moderate physical activity having a significant effect. In a study of 6,013 Japanese men,
Okada and colleagues (65) found that those who engaged in regular physical exercise at
least once a week had a relative risk of T2D of 0.75 (95% CI, 0.61-0.93) compared with men
not engaging in exercise. In a cohort of 34,257 women aged 55 to 69 years, Folsom and
colleagues determined that any level of physical activity was associated with a decreased
risk of developing T2D (RR=0.69, 95% CI=0.63, 0.77) when compared with sedentary
behavior (66). In a study assessing the effects onT2D of physical activity in 37,918 healthy
men where activity levels were classified in metabolic equivalent (MET)-hours per week
and considered either moderate or vigorous, relative risks for T2D across increasing
quintiles of MET-hours per week were 1.00, 0.78, 0.65, 0.58, and 0.51 (P for trend <.001)
(67). Walking pace also was assessed in this study, and walking was found to be efficacious
for preventing T2D. Hu and colleagues (68) assessed data from 6,898 Finnish men and
7,392 women ranging in age from 35 to 64 years to evaluate the relationship of
occupational, commuting, and leisure-time physical activity with the incidence of T2D.
Physical Activity Guidelines Advisory Committee Report G3–10
Part G. Section 3: Metabolic Health
After adjustment for potential confounders, the hazards ratios of diabetes associated with
light, moderate, and active work were 1.00, 0.70, and 0.74 respectively (P=0.020 for trend)
and the authors concluded that high or moderate levels of activity were associated with a
reduced risk of T2D (68). In a prospective cohort study of 37,878 women, a participant was
considered active if she expended more than 1,000 kilocalories on recreational activities per
week, with activity levels being divided into quartiles (69). Physical activity was an
independent predictor of T2D in this study although BMI was a more powerful predictor. In
the Women’s Health Initiative Observational Study, Hsia and colleagues (70) found that
physical activity across exercise quintiles was associated with a decreased risk of T2D
particularly in non-Hispanic white women. This was true for walking (multivariate-adjusted
hazard ratios 1.00, 0.85, 0.87, 0.75, 0.74; P for trend <0.001 across exercise quintiles) and
total physical activity score (hazard ratios 1.00, 0.88, 0.74, 0.80, 0.67; P=0.002).
These data demonstrate a strong inverse relationship of physical activity across quintiles
with diabetes risk in non-Hispanic white women and men. Associations in women of other
races and ethnicites are less clear, but the authors of one study (70) note that the study may
not have been adequately powered to fully assess data from particular race or ethnic
subgroups or possibly that physical activity levels among these groups may not have been
intense enough to allow for analyses (see section below).
Physical Activity Level Versus Cardiorespiratory Fitness
Similar to the questionnaire studies, observational studies that assessed physical activity
levels using objective measures of cardiorespiratory fitness reported that better fitness is
associated with a reduced risk of developing T2D (71-73). Lynch and colleagues (71) found
that in a population-based sample of 897 middle-aged Finnish men, higher cardiorespiratory
fitness was associated with lower risk of developing T2D compared to sedentary persons.
Wei and colleagues (60;72) found that low cardiorespiratory fitness (measured during a
maximal exercise test) and physical inactivity (measured by self-report) were associated
with risk of impaired fasting glucose and T2D as well as all-cause mortality in men with
T2D. In the former study, after adjusting for potential confounders, men in the low-fitness
group (the least fit 20% of the cohort) at baseline had a 1.9-fold risk (95% CI, 1.5- to 2.4fold) of impaired fasting glucose and a 3.7-fold risk (CI, 2.4- to 5.8-fold) of T2D compared
with those in the high-fitness group. In another study, in which cardiorespiratory fitness was
measured during an exercise test and the 6,249 female participants were divided into thirds
by level of fitness, Sui and colleagues (73) found that compared with the least fit third, the
adjusted hazard ratio was 0.86 (95% CI=0.59-1.25) for the middle third and 0.61 (95%
CI=0.38-0.96) for the upper third of cardiorespiratory fitness. Similar to results from studies
using self-report data, results from these studies overall suggest a benefit for achieving and
maintaining increased levels of physical activity (64;66;74;75).
Randomized Controlled Trials of Type 2 Diabetes Prevention
The difficulty of evaluating many of the large RCTs looking at the effects of physical
activity or exercise on diabetes prevention has been to sort out the effects of diet versus
physical activity, as these treatments are commonly combined in large trials. Three large
Physical Activity Guidelines Advisory Committee Report G3–11
Part G. Section 3: Metabolic Health
RCTs have assessed the role of physical activity independently, either using trial design or
by analytic means (Table G3.A7, which summarizes these studies, can be accessed at
http://www.health.gov/paguidelines/report/.). The Da Qing Impaired Glucose Tolerance and
Diabetes Study in China (76) included an exercise-only treatment arm and found that even
modest changes in exercise, without change in diet, reduced the risk of developing diabetes.
The exercise prescription in this study was 1 or 2 units of exercise a day, with units defined
in terms of intensity and duration. One unit was equal to 20 minutes of “mild” exercise (e.g.,
slow walking, shopping, housekeeping), 20 minutes of “moderate” exercise (e.g., fast
walking, cycling), or 10 minutes of “strenuous” exercise (e.g., slow running, stair climbing)
or 5 minutes of very strenuous exercise (e.g., skipping, basketball). In this trial, which was
randomized by clinic rather than by participant, diabetes risk was reduced 46% in the
exercise group, 42% in the diet and exercise group, and 31% in the diet-treated group.
The Diabetes Prevention Study in Finland (77;78) and the Diabetes Prevention Program in
the United States (79) have provided clear evidence that intensive lifestyle modifications,
including strong diet and physical activity interventions, reduce the risk of developing T2D.
Importantly, the role of physical activity is independently beneficial to preventing diabetes.
In the Diabetes Prevention Study, 522 middle-aged, overweight men and women with
impaired glucose tolerance (IGT) were randomized to either lifestyle modification or a
control group (77;78). The physical activity prescription portion of the lifestyle modification
(which included a strong dietary component) was for 30 minutes a day of moderate exercise
for a total of more than 4 hours per week. Incidence of diabetes was very significantly
reduced in the intervention group.
In the Diabetes Prevention Program, 3,234 men and women with IGT and impaired fasting
glucose were randomized into control, medication (i.e., metformin, a drug commonly used
to treat T2D), or lifestyle modification groups. The physical activity prescription portion of
the lifestyle arm (which also had a strong dietary component) was 150 minutes of activity
per week. The lifestyle component reduced incident diabetes by 58% and had a more
powerful effect than metformin (by 39%). In the Diabetes Prevention Program and Diabetes
Prevention Study, weight loss was the dominant predictor of a reduced incidence of
diabetes. However, recent analyses from these studies showed that increased levels of
physical activity prevented diabetes even after adjusting for confounders (80-82).
Physiological Data Showing Benefits of Exercise in Treating Type 2 Diabetes and
Elucidating the Role of Cardiorespiratory Fitness
Type 2 Diabetes is associated with reduced exercise capacity (83;84). Maximal oxygen
consumption was approximately 20% lower compared to nondiabetic persons of similar
weight and physical activity levels in these studies. These exercise abnormalities are present
even in the absence of diabetes-related complications and even in persons with recently
diagnosed T2D. The abnormalities are likely associated with cardiac and hemodynamic
abnormalities (85-87).
Physical Activity Guidelines Advisory Committee Report G3–12
Part G. Section 3: Metabolic Health
It has been well established that a single bout of moderate exercise has a profound effect on
glucose metabolism that may last up to about 18 hours (88). In addition, repeated bouts of
exercise appear to have a cumulative beneficial effect on glucose metabolism. A metaanalysis (89) including 14 studies, provides evidence that regular moderate-intensity
exercise improves metabolic control in T2D. This meta-analysis shows that exercise
significantly improves glycemic control and reduces visceral adipose tissue and plasma
triglycerides, although not plasma cholesterol, in people with T2D, even in the absence of
weight loss. Exercise training in persons with T2D also has a very significant effect in terms
of improving maximal oxygen consumption, measures of submaximal exercise performance,
and other measures of fitness (e.g., 90;91). Available data suggest that these findings are
true for African American women (92) as well as white women. These findings are further
discussed in the section on preventing macrovascular complications of T2D.
Dose-Response Relation
Data on exactly how much physical activity is needed in order to prevent T2D are limited
because such studies have not been prospectively designed. Data from observational studies
indicate that the amounts of effective physical activity range from any increase over
sedentary levels to moderate and vigorous activity levels. It appears, therefore, that any
physical activity may be better than none in terms of preventing diabetes, but better results
are achieved if individuals engage in higher intensity and more frequent physical activity.
Data from several studies support that approximately 30 minutes of moderate intensity
exercise at least 5 days per week provides a substantial (25% to 36%) reduction in the risk of
T2D according to the Nurses’ Health Study (63), the Iowa Women’s Health Study (66), the
Study of Eastern Finns (68), and the Diabetes Prevention Program (79). Importantly, several
of the prospective cohort studies discussed above included walking as a specific modality of
physical activity and all of these found that walking was beneficial in terms of preventing
T2D compared to sedentary behavior (61;63;67;69;70). Thus, data from observational
studies and RCTs support the current recommendation that 2.5 hours per week or typically
30 minutes a day for 5 days a week be performed to prevent T2D. Jeon and colleagues (75)
performed a meta-analysis on the prospective cohort studies that assessed the preventive
effects of moderate-intensity physical activity that could be analyzed independent of
vigorous-intensity physical activity. Moderate-intensity physical activity was defined as an
activity requiring 3.0 to 6.0 METs (75). They identified 10 cohort studies that met these
criteria. These studies in total included 301,121 participants and 9,367 incident cases. Five
of the studies specifically included walking. The summary RR of T2D was 0.69 (95% CI
0.58-0.83) among participants who regularly participated in moderate-intensity exercise
compared to sedentary counterparts. The RR for T2D was 0.70 (0.58-0.84) for walking on a
regular basis (typically briskly for 2.5 hours per week or more) compared to no walking.
However, no data are available to support a specific recommendation for a minimal or even
a lesser dose of exercise. In addition, it is not clear how much additional risk reduction is
obtained with higher levels of physical activity.
Physical Activity Guidelines Advisory Committee Report G3–13
Part G. Section 3: Metabolic Health
Sex and Race/Ethnicity Differences
In observational studies that included women only, 3 large US cohort studies (67-70) all
found that greater physical activity was associated with a lower incidence of diabetes.
However, in one study, this relationship was present only in non-Hispanic white women and
not in women of African American, Hispanic or Asian descent (70). These findings await
confirmation in further studies because the study may not have been powered to detect
differences across all race or ethnic groups. Results were based on self report of diabetes in
the total population but were confirmed in a subset who also provided blood samples and
physician reports.
Data from RCTs as well as observational studies suggest clearly that overall, increased
levels of physical activity play a beneficial role in preventing T2D for both women and men.
In the Diabetes Prevention Program (93), treatment effects did not differ significantly
according to sex, race, or ethnic group. Lifestyle factors addressed in the Program included
diet and physical activity, and both had an independent effect on preventing T2D. Although
participant numbers became too small for clear results when grouped by ethnicity, it appears
that risk reduction compared with placebo was greater for the lifestyle group than for the
metformin group in non-Hispanic whites (50% versus 12%, respectively) and Hispanics
(57% versus 2%, respectively) (94). African Americans (42% versus 29%) and Native
Americans (43% versus 42%), showed similar efficacy for the lifestyle and metformin
groups. However, for Asian Americans, metformin showed a nonsignificantly greater
reduction than intensive lifestyle intervention (62% versus 30%). Neither lifestyle nor
metformin showed significant heterogeneity across the 5 ethnic groups in terms of efficacy.
Subsequent studies in India and Japan (95;96), as well as the Da Qing study in Chinese
people (76), similarly found an independent effect of physical activity in preventing T2D,
and the findings were true for men and women and appeared to be true for all ethnic groups
involved.
Thus, overall, acknowledging the limited data available to date, no strong evidence is
available to negate the data suggesting that physical activity prevents T2D in men and
women of different race and ethnic groups, although further research should explore this
important issue.
Youth
Type 2 Diabetes is growing in prevalence in children and adolescents. Alarmingly, unlike
youth who do not have T2D, youth with this condition often have CV risk factors, such as
hypertension and dyslipidemias as well. Thus, potentially, youth who have T2D may
develop CVD at relatively young ages (97;98). Data from RCTs show that increased
physical activity improves insulin sensitivity in obese youth, although longitudinal data are
limited (99-101) and the effects on CV risk factors are not well established because trials are
lacking. A recent review has highlighted the efforts of different interventions to address
obesity in youth of various ethnic and racial groups. These interventions focused on lifestyle
changes including increased physical activity (102), and several had a physical activity-only
component (103;104). Overall findings were encouraging. The studies of both Sallis and
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colleagues (103) and Pangrazi and colleagues (104) showed that school-based programs
promoting increased physical activity were effective at increasing the physical activity level
or cardiorespiratory endurance (although not in reducing BMI) of girls especially.
No RCTs have been completed that show that physical activity or exercise prevents T2D in
youth although it is likely give results in aduls. To date, the limited intervention and
observation studies suggest that to prevent and manage T2D, daily goals for youth should
include less than 60 minutes of daily screen (television, computer or video game) time and
60 to 90 minutes of daily physical activity (105-107). A large multicenter trial (the TODAY
study) is currently underway to assess the role of physical activity in preventing T2D in
youth (108).
Resistance Training
Resistance training has shown promise as a modality for treating diabetes (109;110). Sigal
and colleagues (111) found, in a group of 251 individuals with T2D, that both aerobic and
resistance training individually improved glycemic control, but improvements were greatest
with combined aerobic and resistance training. However, this exercise modality has not been
explored for its role in prevention of T2D in large trials, and no data currently exist showing
that resistance training plays a role in preventing T2D. Future studies should further
investigate the role of resistance training in preventing T2D given the beneficial effects of
such training on the metabolism of persons with T2D.
Safety of Physical Activity and Exercise for Persons With Type 2 Diabetes
The consensus is that the benefits of exercise for persons with T2D far outweigh the risks.
However, safety concerns about exercise in this group have been voiced. These concerns
range from cardiovascular risks associated with physical activity and exercise to caution
about hypoglycemia and foot care concerns. The American Diabetes Association (ADA)
guidelines on safety (112;113) provide a comprehensive review of safety issues and
measures, although the recommendations lack supporting data in some cases.
Question 3. Does Physical Activity Have a Role in Reducing
Macrovascular Risks in Type 2 Diabetes?
Conclusions
Strong data support the benefits of physical activity and fitness for CVD protection in T2D
and IGT. The data are stronger for hard outcomes, such as CVD events and mortality, than
for known CVD risk factors, but this may be an artifact of the relatively short duration of
risk factor studies and the potential for small changes in risk factors to have a large
cumulative impact on outcomes. These data suggest that a minimum of moderate-intensity
aerobic activity for more than 2 hours per week is necessary to achieve significant benefit,
and that near maximum benefit may be achieved with moderately vigorous aerobic activity,
such as brisk to very brisk walking, for 3 to 7 hours per week (about 12 to 21 MET-hours
per week). Combined aerobic and resistance activity appears to have greater benefits than
Physical Activity Guidelines Advisory Committee Report G3–15
Part G. Section 3: Metabolic Health
either type alone when CVD risk factors (and non-CV effects) are considered, but CVD
outcome data for activity other than aerobic activity are lacking. In general, the existing data
for CVD risk reduction in persons with T2D are consistent with a recommendation of an
aerobic activity program with a goal of at least 120 minutes per week and preferably more
than 180 minutes per week of moderate to moderately vigorous activity.
Rationale
Several studies have specifically considered the effects of physical activity on CVD risk
factors and outcomes in T2D. Observational studies have shown that, among persons with
this condition, those who exercise or are more fit have a reduced risk of CV morbidity and
mortality than do less active or less fit individuals (67;114-118) (Tables G3.A8 and G3.A9,
which summarize these studies, can be accessed at http://www.health.gov/paguidelines/
report/.). A study of more than 3,000 Finns with T2D found that all types of physical activity
(e.g., recreational and occupational) are beneficial in reducing CV events and mortality
(117). Following is a review of the evidence for benefits, dosage, and type of physical
activity specifically for reduction of CVD risk and outcomes in T2D.
Cardiovascular Disease Risk Factor Reduction
Many cross-sectional studies have found inverse correlations between physical activity level
and various CVD risk factors in T2D populations. Two meta-analyses of these studies have
been performed (119;120). One focused on lipid effects and hemoglobin A1c (HbA1c) and
found a small (5%) but significant decrease in low-density lipoprotein (LDL) cholesterol
(−6.4 mg/dl, range = −11.8 to −1.1) and a strong trend toward improved HbA1c (−0.4%,
range = −0.8 to 0.0), but no change in total cholesterol or triglycerides (120). This section
focuses on a recent meta-analysis of controlled intervention studies in subjects with T2D
that compared different exercise interventions for their effects on CVD risk factors (119).
The meta-analysis covers about 1,000 subjects, aged 48-62 years. Exercise interventions
were of aerobic, resistance, or combined types. Overall conclusions from the analysis were
that all forms of exercise improved insulin sensitivity, with combined types having the
greatest effect (especially in men) and resistance alone the least. Combined exercise also had
small and moderate benefits on systolic and diastolic blood pressure, respectively, and a
small benefit on raising high-density lipoprotein (HDL) levels. Aerobic exercise also
benefited triglyceride levels and systolic blood pressure. Resistance exercise did not show
significant benefit on any CVD risk factor. Another recent prospective trial with a 6-month,
twice weekly, progressive, supervised aerobic program in a population with T2D also
demonstrated improved HDL levels (12%) and marked decreases in markers of endothelial
dysfunction (ICAM-1 and P-selectin), but no changes in inflammatory markers (hsCRP and
TNF-alpha) or LDL levels (121).
Cardiovascular Disease Outcomes
Only one intervention study and no randomized trials have addressed the effect of activity or
fitness on hard CVD outcomes. The ongoing Look AHEAD (Action for HEAlth in
Diabetes) trial, currently underway, is a randomized long-term study addressing hard CV
Physical Activity Guidelines Advisory Committee Report G3–16
Part G. Section 3: Metabolic Health
outcomes after an intervention (122-124). However, the intervention is targeted at weight
loss by a combined program of diet and physical activity and thus will not address the effect
of physical activity in isolation. In the one existing interventional trial looking at physical
activity alone, Shinji and colleagues followed a small group (n=102) of T2D adults for 17
months after institution of a single, modest, home-based exercise program (walking 20 to 30
minutes, 4 to 6 times per week, at anaerobic threshold) (125). Incident CVD was much
higher in “dropouts” than in “completers” even after adjustment for multiple parameters
with a RR for incident CVD of 16.5 (95%CI, 1.19-228) for dropouts versus completers. This
study suggests that low-level physical activity is beneficial for primary CVD prevention in
people with T2D. However, no data were reported or adjustments made for smoking or diet,
the “dropouts versus completers” study comparison was nonrandomized, the number of
events was very small (n=8), and the confidence interval was very large.
Several prospective cohort studies have found that CV fitness (60;126-128) (Table G3.A8)
and physical activity level (60;67;115-118;129;130) (Table G3.A9) are inversely correlated
with mortality (all-cause and CVD) and/or CVD event rates in subjects with T2D. Some of
these studies have evaluated the effect of frequency, duration, and/or intensity of physical
activity on the protective effect. A follow-up of the National Health Interview Survey of
2,896 adults with T2D (115) found that walking for more than 2 hours per week (but not
more than 0 hours to 1.9 hours) was associated with a significantly decreased hazard ratio
(HR) for CVD mortality (HR = 0.59, 95% CI 0.40 to 0.87, P for trend 0.03 after exclusion
of disabled subjects, and after adjusting for age, sex, race, BMI, self-rated health, smoking,
weight loss approaches, hospitalizations, hypertension or medications, physician visits,
limitations caused by CVD or cancer, and extent of functional limitation).
In the Nurses’ Health Study of more than 5,000 diabetic women followed for 14 years,
subjects were placed in 5 groups based on hours of total moderate-vigorous activity per
week, including non-leisure activities (67). RR for CVD events (fatal and nonfatal
myocardial infarction or stroke) decreased progressively with increasing weekly volume of
moderate to vigorous activity (less than 1, 1 to 1.9, 2 to 3.9, 4 to 6.9, and 7 or more hours
per week). Age-adjusted relative risks were 1.0, 0.93 (95% CI, 0.69 to 1.26), 0.82 (95% CI,
0.61 to 1.10), 0.54 (95% CI, 0.39 to 0.76), and 0.52 (95% CI, 0.25 to 1.09) (P for trend
<0.001). This relationship did not change appreciably after adjustment for smoking, BMI,
and other CV risk factors. Among women who primarily walked for exercise, both increased
pace (easy pace: 1.0, average pace: 0.52, brisk pace: 0.47, P for trend 0.001) and weekly
MET walking score were inversely associated with CVD event risk. Among women who did
not exercise vigorously in addition to walking, multivariate relative risks across quartiles of
MET scores for walking were 1.0, 0.85 (0.62-1.34), 0.63 (0.36-1.10), 0.56 (0.31-1.00) (P for
trend 0.03) for 0 to 0.5, 0.6 to 2.7, 2.8 to 7.5, and more than 7.5 MET hours per week of
walking.
In the Health Professionals follow-up study, Tanasescu and colleagues followed about 2,800
men with T2D for 14 years and assessed incident CVD (fatal or nonfatal MI or stroke)
(116). Risk of total and fatal CVD events showed a statistically significant improvement
Physical Activity Guidelines Advisory Committee Report G3–17
Part G. Section 3: Metabolic Health
with increasing physical activity after age-adjustment (P for trend 0.02, 0.03, respectively)
and a strong trend after multivariate analysis (adjusted for alcohol intake; smoking; family
history of myocardial infarction; use of vitamin E supplements; duration of T2D; diabetes
medication; quintiles of dietary intake of trans fat, saturated fat, fiber, and folate; history of
angina and coronary artery bypass graft; and baseline presence of hypertension and high
serum cholesterol; P for trend 0.07, 0.13, respectively). Additional adjustment for BMI
further attenuated the trend (for total CVD events: 1.0, 0.91 [0.63-1.31], 0.68 [0.45-1.02],
0.76 [0.51-1.14], and 0.72 [0.47-1.09] by quintile; P for trend 0.14). Their results suggest
that physical activity protects from CVD events, especially fatal events, and that for T2D,
moderate energy expenditure (3rd quintile, 12 to 22 MET-hours per week, corresponding to
about 3 to 5 hours per week of brisk walking) provides the most protection. The authors
state that this was not the case in the non-diabetic cohort where a more continuous doseresponse was seen. A separate walking intensity multivariate analysis suggests that for those
who walked for exercise, the higher the walking speed, the greater the protection. After
adjustment for CVD risk factors, walking time, and other vigorous activity, the relative risks
for normal pace (2 to 2.9 miles per hour), brisk pace (3 to 3.9 miles per hour), and very brisk
pace (more than 4 miles per hour) were 0.82, 0.58, and 0.17 (95% CI 0.04 to 0.71; P for
trend <0.001) compared to an easy pace (less than 2 miles per hour).
The studies described above suggest that maximum benefit may be achieved with substantial
volumes of moderately vigorous exercise, such as brisk to very brisk walking, for 3 to 7
hours per week. It is interesting to speculate that subjects with T2D may differ from nondiabetic subjects in their response to very vigorous exercise, but further studies are needed to
fully address the intensity response of CVD risk reduction with physical activity in T2D.
In the Whitehall Study, Batty and colleagues performed a comparative study of the benefits
of physical activity in men with T2D or IGT (Table G3.A9) compared to men with normal
glucose tolerance (131). After adjustment for other factors, physical activity remained an
independent predictor of all-cause, CHD, and other CVD mortality. The gradient for benefit
with increasing physical activity was much steeper for the IGT/T2D subjects than for those
with normal glucose tolerance, suggesting a greater benefit for metabolically impaired
subjects than for the general population. A plot adapted from this data illustrates that the
highest level of physical activity actually eliminated the excess CHD mortality associated
with IGT and T2D (132) (Figure G3.4).
Others have also found a steeper response of CVD risk to physical activity in diabetic
subjects, but most studies have found that CVD risk remains greater in diabetic than nondiabetic subjects even in the most active subgroups (116).
Physical Activity Guidelines Advisory Committee Report G3–18
Part G. Section 3: Metabolic Health
Figure G3.4. Physical Activity/Exercise and Macrovascular Risk Reduction in
Type 2 Diabetes
Note: Age-adjusted cardiovascular disease mortality rates by leisure time activity in normoglycemic men (n=6,056) versus
men with impaired glucose tolerance/diabetes (n=352) in the Whitehall Study (Adapted by Gill and Malakova 2006, (132)
from data from the Whitehall Study). P=0.006 for trend in normoglycemic men, P=0.003 for trend in men with IGT/diabetes.
Source: Gill JM, Malkova D. Physical activity, fitness and cardiovascular disease risk in adults: interactions with insulin
resistance and obesity. Clin Sci (Lond). 2006 Apr;110(4):409-425. Review. Reproduced with permission.
Physical Activity, Cardiovascular Fitness, and Type 2 Diabetes
A recent meta-analysis evaluated the benefits of physical activity for CV fitness in persons
with T2D (133). The overall analysis of 9 randomized, controlled, prospective interventional
studies had mean exercise characteristics of 3.4 sessions per week and 49 minutes per
session for 20 weeks. Mean baseline maximal oxygen consumption of 22.4 ml/kg/min
increased 11.8% in the exercise arms and decreased 1.0% in the control arms. Magnitude of
improvement in maximal oxygen consumption and in HbA1c correlated better with exercise
intensity than with exercise volume. Because fitness and glycemic control appear to benefit
overall and CVD mortality, this suggests that more intense exercise would have greater
mortality benefits. However, the possibility of a mortality impact of intense exercise in
diabetic people cannot be ruled out and is, in fact, suggested by some outcome studies
(discussed above). Furthermore, overt nephropathy, peripheral neuropathy, and retinopathy
present in many diabetic individuals may be contraindications to very vigorous activity,
prolonged stepping activities, and weight-lifting or high-impact activities, respectively,
Physical Activity Guidelines Advisory Committee Report G3–19
Part G. Section 3: Metabolic Health
though these recommendations appear to be based on little experimental evidence (see
Question 5. Does Physical Activity Have a Role in Preventing and Treating Diabetic
Microvascular Complications?).
Question 4. Does Physical Activity Have Benefits for Type 1
Diabetes?
Conclusions
Data are more limited for type 1 diabetes (T1D) than for T2D, but generally support benefits
of exercise for T1D in reducing mortality, CVD risk factors, and microvascular
complications. Data are weaker for benefits for glycemic control, and CVD outcomes have
not been studied. Data regarding the optimal exercise prescription also are limited. This may
still include limiting exercise appropriately in proliferative retinopathy. However, any
exercise prescription in T1D also must address the issue of avoiding exercise-induced
hypoglycemia. This requires an individualized approach that includes modifying insulin
dosing, ingesting additional carbohydrates, and ensuring appropriate details of the exercise
prescription.
Rationale
Though T1D is less prevalent than T2D, it remains among the most prevalent chronic,
serious diseases of childhood affecting about 1.5/1,000 children in the United States (134).
Overall prevalence estimates are increasing now that it has been recognized that a quarter to
a half of all T1D develops in adults. Although the metabolic abnormalities associated with
insulin resistance have not been considered major factors in this autoimmune form of
diabetes, CVD has long been known to be a major cause of morbidity and mortality in T1D.
It is now becoming recognized that insulin resistance is also present in T1D and that this
may contribute to the associated excess CVD risk. As T1D individuals spend a longer
portion of their lives with absolute endogenous insulin deficiency and relative insulin
sensitivity, hypoglycemia is a greater safety concern in T1D than in T2D. Effects of physical
activity on CVD risk factors and glycemic control and safety concerns are addressed in this
section. Microvascular complication effects are addressed in a later section (see Question 5.
Does Physical Activity Have a Role in Preventing and Treating Diabetic Microvascular
Complications?).
As with T2D and non-diabetic populations, exercise has been shown to be inversely
correlated with mortality in T1D. In a cohort study of 548 T1D subjects followed for 7 years
in the Pittsburgh Insulin-dependent Diabetes Morbidity and Mortality Study, sedentary
males were 3 times as likely to die as active males (135). The relationship did not achieve
statistical significance in women.
Physical Activity Guidelines Advisory Committee Report G3–20
Part G. Section 3: Metabolic Health
Physical Activity and Type 1 Diabetes Prevention
No data exist to show that habitual physical activity or exercise plays a role in preventing
T1D.
Physical Activity and Type 1 Diabetes Treatment
Glycemic Control
Exercise increases insulin sensitivity and induces non-insulin dependent skeletal muscle
glucose uptake. Overweight or otherwise insulin resistant T1D individuals will derive
benefit from the improvement in insulin sensitivity that accompanies exercise in the same
way that T2D individuals do (see Question 1. Does Physical Activity Have a role in
Preventing or Treating Metabolic Syndrome?). Recent evidence suggests that even
apparently insulin sensitive diabetic individuals are insulin resistant compared to nondiabetic controls (136;137). Theoretically, therefore, most or all T1D patients might be
expected to improve insulin sensitivity with physical activity. As such, it would seem that
exercise could improve glycemic control. However, for a T1D patient on a regular dose of
insulin, this improved sensitivity comes at the cost of an increased risk of hypoglycemia and
resultant hyperglycemia. Furthermore, high-intensity exercise increases catecholamine
release and can cause post-exercise hyperglycemia. Thus, studies have had mixed results.
Nevertheless, the largest studies have demonstrated improved glycemic control with
physical activity in T1D. Interventional studies, most from the 1980s, have all been small
(Table G3.A10, which summarizes these studies, can be accessed at http://www.health.gov/
paguidelines/report/.). Most have used a moderate aerobic exercise program and have had
mixed results, with some negative (138-144) and some modestly positive (145-148) trials.
One of the positive trials included a “carbohydrate control” diet intervention in addition to
exercise (145). Thus, the improved glycemic control in this study cannot clearly be
attributed to exercise. Other positive studies did not include any dietary change or
monitoring. Some negative trials followed caloric intake and noted an increase in calories in
the exercise group (139). Few studies have looked at resistance training. Two studies with
resistance interventions were split, one with improvement in HbA1c (148), the other without
(143). Larger cross-sectional studies have also been split (Table G3.A11, which summarizes
these studies, can be accessed at http://www.health.gov/paguidelines/report/.). Ligtenberg
studied 200 subjects and found no correlation between self-reported activity and HbA1c
(149). The FinnDiane study of 1,030 T1D subjects found a sex-based difference in that selfreported physical activity did correlate with improved HbA1c in women, but not in men
(150). The effect on HbA1c in women was an 0.5% decrease in both the moderately active
(10 to 40 MET-hours per week) and active groups (more than 40 MET-hours per week). In
contrast, in men, insulin doses were decreased to a greater extent in the more active
populations. In the largest study to date, Herbst and colleagues studied more than 23,000
subjects with T1D and found a small, but highly significant improvement in HbA1c (0.3%)
in the 2 active groups (exercise 1 to 2 times a week and 3 or more times a week) compared
to the sedentary group (151). Only one study compared resistance to aerobic training and
found no benefit for glycemic control in either arm (143). Overall, good evidence for a
significant role for exercise alone in glycemic control is limited. Existing evidence suggests
Physical Activity Guidelines Advisory Committee Report G3–21
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that a modest improvement in glycemic control occurs with small amounts of activity and
does not increase with more frequent or more intense exercise. More studies are needed to
further clarify the role of physical activity in T1D because many of the studies are relatively
old.
Macrovascular Complications
CVD risk factors. The FinnDiane study found that low physical activity correlated with the
presence of metabolic syndrome in TID, especially the waist circumference component
(152). Lehman and colleagues found significant improvements in insulin sensitivity, LDL,
HDL, blood pressure, and waist-to-hip ratio with a self-monitored increase in physical
activity of about 150 minutes per week without an increase in severe hypoglycemic events
(153). Few studies have investigated the effect of different doses or types of exercise on
CVD risk factors in TID. In one 12-week intervention study, Ramalho and colleagues
compared the effects of thrice weekly 40 minutes of moderate aerobic training to resistance
training (143). Neither group improved lipid profiles, but the aerobic group had improved
waist circumference while the resistance group did not.
CVD outcomes. No data exist on the effect of physical activity on actual CV outcomes
specifically in T1D.
Physical Activity, Type 1 Diabetes, and Risk of Hypoglycemia
Whatever the benefits of exercise in T1D, it is clear that they come at the expense of an
increased risk of hypoglycemia, both during and up to 30 hours after exercise. However, the
ADA Position Statement on Physical Activity and Exercise states the “all levels of physical
activity, including leisure activities, recreational sports, and competitive professional
performance, can be performed by people with T1D who do not have complications and are
in good glucose control”(154, p.61). This is because it is possible, with a good
understanding of the physiologic responses to exercise, to manage exercise and postexercise blood sugars. Guidelines for hypoglycemia control have been published, although
they are not always strongly data-based and therefore are outside the scope of this section.
(155-162).
Question 5. Does Physical Activity Have a Role in Preventing and
Treating Diabetic Microvascular Complications?
Conclusions
Physical activity may prevent the development of diabetic neuropathy and diabetic
nephropathy (primary prevention) in those with T1D and T2D. Though uncontrolled
observational studies suggest physical activity may treat diabetic neuropathy and
nephropathy, RCTs are necessary to confirm this. Other observational studies suggest no
effect of physical activity on either the prevention or treatment of diabetic retinopathy in
T1D subjects. No data are available on sex differences or dose-response of physical activity.
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Moderate-intensity physical activity appears safe for all individuals with diabetes even those
with existing diabetic microvascular complications, although vigorous-intensity activity,
high-impact exercise, or weight-bearing exercise may possibly lead to adverse outcomes in
those with existing proliferative retinopathy, severe nephropathy with renal osteodystrophy,
or severe neuropathy, respectively. Exercise stress testing is not recommended before
starting a moderate-intensity exercise regimen and is of controversial benefit before
initiating a vigorous intensity aerobic exercise program.
Introduction
Persons with diabetes have a highly increased prevalence of microvascular complications,
which are associated with substantial morbidity. In this section, the role of physical activity
in preventing and treating microvascular complications in those with T1D and T2D will be
discussed. For the purpose of this document, microvascular complications of diabetes are
defined to include neuropathy (based either on symptoms, physical examination, or
abnormal electromyogram findings consistent with this diagnosis), nephropathy (defined as
microalbuminuria, macroalbuminuria, or decreased calculated glomerular filtration rate),
and retinopathy (defined as non-proliferative or proliferative retinopathy diagnosed by an
ophthalmologist using retinal photographs).
To date, no large RCTs have investigated the role of exercise training or physical activity in
preventing or treating diabetic microvascular complications. One small RCT and some
observational studies have suggested a possible relationship between physical activity and
both the primary prevention and treatment (tertiary prevention) of diabetic microvascular
complications. One meta-analysis (119) has evaluated the impact of physical activity on a
surrogate intermediate marker (HbA1c) for progression to diabetic microvascular
complications, and showed convincingly that physical activity interventions lower HbA1c.
Because better glycemic control has been shown to decrease the incidence of diabetic
microvascular complications in subjects with T1D (163) and T2D (164), it is possible that
exercise training could reduce microvascular complications solely due to its general
improvement of glycemic control. However, the overall lack of studies in this area means
that the role of physical activity in preventing microvascular complications remains
inconclusive. Specific gaps in the literature that warrant further research are large studies to
determine the exercise dose-response curve for prevention or treatment of microvascular
complications, and determining whether differences exist by subject race/ethnicity, sex, T1D
vs. T2D, or exercise modality.
The next three sections will summarize what is known regarding the role of physical activity
in preventing and treating 1) diabetic neuropathy, 2) diabetic nephropathy, and 3) diabetic
retinopathy. Safety concerns for exercise in these populations also will be discussed.
Rationale
Observational studies provide most of the existing data, which are of limited scope and
quality, to determine the role of physical activity in primary prevention of diabetic
Physical Activity Guidelines Advisory Committee Report G3–23
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nephropathy, neuropathy, and retinopathy. Observational studies of lesser quality (often
uncontrolled) have been performed to address the role of physical activity for treatment of
diabetic nephropathy, neuropathy, and retinopathy. To determine the safety of physical
activity with existing microvascular complications, small observational studies have been
performed and clinical standards of care also have been discussed when appropriate to
supplement the scarce amount of safety data.
Diabetic Neuropathy
One small RCT (165), one cross-sectional study (166), and one retrospective cohort study
(167) have evaluated the impact of physical activity on primary prevention of diabetic
neuropathy (Table G3.A12, which summarizes these studies, can be accessed at
http://www.health.gov/paguidelines/report/.). From these limited data, no firm conclusions
may be drawn but it does appear that physical activity may possibly have some role in
preventing diabetic neuropathy. The RCT data, although only based on 78 participants (73%
with T2D), revealed a reduction in both motor and sensory neuropathy from 4 years of
moderate-intensity exercise despite no significant weight loss (165). Of the 2 cross-sectional
studies performed in T1D subjects addressing neuropathy, one showed physical activity
significantly benefited males only (166), while the other had no effect (167).
Treatment of Diabetic Neuropathy
No studies have evaluated the use of physical activity to treat diabetic neuropathy. One
study evaluated 12 months of physical activity in conjunction with a dietary intervention for
prediabetic neuropathy (Table G3.A13, which summarizes these studies, can be accessed at
http://www.health.gov/paguidelines/report/.), using a pre-post study design in 40 subjects
with prediabetes to show significant differences in nerve fiber density at the proximal
portion of the leg (P <0.05), and non-significant improvement in neuropathic pain and nerve
fiber density at the distal portion of the leg (168).
With respect to diabetic ulcer prevention in a group with diabetic neuropathy, no significant
improvement in the surrogate outcome of dorsal foot cutaneous perfusion was found after
either a 10-week aerobic exercise (169) or 8-week resistance exercise program (170).
Although significant differences were initially described in dorsal foot cutaneous perfusion
between physically active individuals with T2D as compared with sedentary individuals
with T2D who had a higher mean HbA1c (171), no differences were evident when this study
was repeated with similar HbA1c levels between groups (172). This area requires further
study.
Safety of Exercise With Diabetic Neuropathy
Three different aspects of safety of exercise with comorbid neuropathy are at issue:
(1) Safety of exercise with autonomic neuropathy, (2) Ulcer risk with existing neuropathy,
(3) Fall risk with existing neuropathy.
Physical Activity Guidelines Advisory Committee Report G3–24
Part G. Section 3: Metabolic Health
Safety of exercise with autonomic neuropathy. Existing guidelines are not based on data
and are therefore are outside the scope of this chapter. Graham and Lasko-McCarthy and
Sigal and colleagues provide further information on this topic (112;173).
Ulcer risk with existing neuropathy. Two studies observed an inverse relationship between
physical activity and ulcer incidence (174;175). However, 2 other studies have suggested
that abrupt increases in activity may increase the short-term risk of ulceration. Armstrong
and colleagues found a significantly greater coefficient of variation in the group with
recurrent ulcer (174) and Lemaster and colleagues (175) found a significant unadjusted
increased risk of ulcer with increased short-term activity. Ulcer risk was increased with
greater intensity and duration of loading pressure on the feet while walking (176;177)
possibly showing a clinical benefit to protective diabetic footwear in this population.
Risk of falls with existing neuropathy. Several studies have evaluated the degree to which
gait is altered by diabetic neuropathy (suggesting attendant increased fall risk), with one
study showing a targeted intervention may improve balance in this population. Dingwell and
colleagues as well as other researchers have performed studies showing decreased walking
speeds or decreased gait variability (176;178-180) in those with diabetic peripheral
neuropathy versus non-diabetic controls. Giacomozzi and colleagues also showed those with
diabetic neuropathy and a prior foot ulcer had even greater gait variability than those with
neuropathy and no prior ulcer (176). Mueller and colleagues showed that the peak torque
generated during plantar flexion and the range of motion of dorsiflexion at the ankle are
strongly correlated (r = 0.78) and contribute to the power generated from the ankle joint
during ambulation (181). These data suggest that decreased ankle dorsiflexion range of
motion and/or plantar flexion strength are associated with decreased step length and speed
during walking (181). Novak and colleagues (182) reported that 30 individuals with T2D
and associated diabetic neuropathy described worse foot pain and walked shorter distances
than subjects with T2D without neuropathy and non-diabetic controls, with strong
correlation between pain level and walking distance (r = -0.45, P <0.001) (182).
The data presented here generally support the pragmatic exercise precautions recommended
in clinical practice guidelines (Table G3.A14, which summarizes these studies, can be
accessed at http://www.health.gov/paguidelines/report/.). Those with severe peripheral
neuropathy should use non-weight bearing activities to avoid foot ulceration or Charcot joint
destruction (112;173), and all individuals with diabetes should use appropriate footwear and
inspect their feet daily to reduce injury risk (183).
Diabetic Nephropathy
Four cross-sectional studies (150;152;166;184) and 1 retrospective cohort study (167) have
evaluated the impact of physical activity on diabetic nephropathy prevention in subjects with
T1D (Table G3.A12). These data are not available in patients with T2D. From these limited
data, no firm conclusions may be drawn but they suggest physical activity may prevent
diabetic nephropathy. In 2 separate cross-sectional analyses of slightly different subsets of a
Finnish population with T1D, less physical activity was associated with greater prevalence
Physical Activity Guidelines Advisory Committee Report G3–25
Part G. Section 3: Metabolic Health
of nephropathy (150;152). A significant association was observed between greater leisuretime physical activity and decreased nephropathy in men only, with no increased risk in
women with T1D (166). The other 2 observational studies performed showed neither harm
nor benefit in prevention of diabetic nephropathy (167;184).
Physical Activity To Treat Diabetic Nephropathy
A pre-post analysis (185) evaluated the effect of 3 weeks of physical activity and lowcalorie diet in treating existing nephropathy (Table G3.A13) in subjects with T2D. Although
albuminuria was reduced, the dietary intervention and/or associated weight loss may have
confounded these results. These data are somewhat promising but inconclusive.
Safety of Physical Activity With Existing Nephropathy
The relevant literature appears to show that exercise does not worsen resting proteinuria
(186-188). In a cohort of 373 subjects with T1D, a strong correlation between overnight
albumin excretion rate (AER) and post-exercise AER existed (r = 0.74, P <0.001), and 52%
of subjects had an elevated overnight AER preceding an elevated post-exercise AER (186).
In a smaller cross-sectional study, Groop and colleagues (187) showed exercise did not
increase protein excretion in 17 subjects newly diagnosed with T1D, but that 17 subjects
with long-standing T1D had a significant increase in post-exercise excretion of albumin,
β2-microglobulin, Kappa light chains, and IgG independent of whether resting AER was
elevated (n=7) or normal (n=10). A small cohort study found no significant difference in
time for nephropathy progression in 6 subjects with “good” unrestricted physical activity as
compared with 7 subjects with “self-restricted” physical activity (188).
Despite hypothetical adverse effects of increased proteinuria immediately after exercise
(189), existing data show no progression of nephropathy with exercise and, in fact,
increasing physical activity may decrease existing albuminuria, as described earlier in this
section (185;190;191). In the absence of primary data for other safety considerations in
those with diabetic nephropathy, a review of these issues is outside the scope of this
discussion, although guidelines exist (112;173).
Diabetic Retinopathy
One moderate-sized prospective cohort study (192), and several cross-sectional
(150;152;166;184;193) and retrospective (167;194) observational studies have evaluated the
impact of physical activity on diabetic retinopathy (Table G3.A12) in T1D. These limited
data suggest that physical activity does not influence the risk of developing diabetic
retinopathy. The moderately sized cohort study (192) observed no difference in the
incidence of retinopathy over 6 years in 606 T1D subjects with respect to current physical
activity or historical participation in team sports, in contrast to an earlier cross-sectional
analysis (193) in a subset of the same cohort population where a decreased prevalence of
retinopathy in women who played team sports (OR 0.46, P <0.05) or who reported current
strenuous physical activity (OR 0.34, P <0.05) was previously observed. Two crosssectional analyses of slightly different subsets of a Finnish population with T1D found no
Physical Activity Guidelines Advisory Committee Report G3–26
Part G. Section 3: Metabolic Health
association between physical activity and retinopathy (150;152) despite an association
between physical activity and less nephropathy in those same studies (150;152). Of the 4
other cross-sectional studies performed, none showed any benefit or harm of physical
activity in the prevention of diabetic retinopathy (166;167;184;194).
Treatment of Diabetic Retinopathy
A large cohort study reported no impact of self-reported current or historical physical
activity measurements on retinopathy in a large cohort of T1D subjects with both nonproliferative and proliferative retinopathy at baseline measurement (192).
Safety of Physical Activity With Existing Diabetic Retinopathy
Although existing data raise concerns about the plausible causality of exercise-induced
vitreous hemorrhages individuals with diabetic retinopathy, existing data have not
conclusively shown a risk of moderate-intensity exercise in those with this condition (195).
The 2 prospective studies evaluating the safety of exercise in humans with existing
retinopathy have not shown an increased risk of retinopathy progression or of vitreous
hemorrhage in this population. The prospective cohort study analysis by Cruickshanks and
colleagues showed no risk of worsened retinopathy in those with T1D who were more
physically active over a 6-year period as compared with their more sedentary counterparts,
including a very small subset of self-described weight lifters (192). A pre-post exercise
intervention study in 30 subjects with T1D or T2D and existing proliferative diabetic
retinopathy (90% or greater) or diabetic macular edema observed no newly documented
vitreous hemorrhages attributable to a 12-week supervised exercise training program,
although the study was under-powered to definitively determine vitreous hemorrhage risk
(196).
Given the preceding evidence, clinical providers have generally recommended moderateintensity exercise but advised against vigorous exercise regimens for those with proliferative
retinopathy (112;173;183;197) and severe nonproliferative retinopathy (112) due to the
theoretical (yet unproven) increased risk for vitreous hemorrhage and retinal detachments
with vigorous exercise.
Cardiovascular Safety of Physical Activity With Existing Microvascular
Complications
Despite a lack of studies evaluating this practice, the most recent published standards of care
suggest that diabetic subjects with more than a 10% 10-year risk for CV disease by the
United Kingdom Prospective Diabetes Study risk calculator (198) should consider exercise
stress testing to screen for latent ischemia before initiating vigorous aerobic exercise
regimens that exceed the “demands of everyday living” (199).
Physical Activity Guidelines Advisory Committee Report G3–27
Part G. Section 3: Metabolic Health
Question 6: Do Physical Activity and Exercise Have a Role In
Preventing Gestational Diabetes?
Conclusions
Although no RCTs have been performed to demonstrate that physical activity can prevent
gestational diabetes (GDM), data from observational studies support that concept. Available
studies suggest that approximately 30 minutes per day of moderate-intensity physical
activity is likely a sufficient dose to decrease the GDM risk (200). However, this suggestion
is based on relatively few studies, and further studies should directly address the issue of
dose-response.
Introduction
Gestational diabetes is defined as diabetes first identified during pregnancy. Overall,
prevalence rates of GDM have increased from 1.9% in 1989-1990 to 4.2% in 2003-2004, a
relative increase of 122% (201). The prevalence of GDM is 17% in obese women, and
overweight women have a significantly greater risk of developing GDM than do nonoverweight women (202). It is estimated that up to 60% of women with GDM will develop
T2D within 4 years of delivery (203). GDM can give rise to many adverse outcomes both to
mother and infant. It is associated with a greater likelihood of Caesarean section deliveries
and other birth complications (204). Women with GDM also are more likely to have a
difficult labor and delivery. Babies of women with GDM are at increased risk of obesity and
diabetes later in life as well as other comorbid conditions at birth (205).
Given that women who develop GDM are at highly increased risk of developing T2D,
understanding how to prevent and treat GDM is very important. The role of physical activity in
preventing and treating GDM has not been as well studied as for T2D. Indeed, no RCTs have
assessed whether GDM can be prevented by regular physical activity. However, observational
epidemiologic studies suggest overall that this may be the case (Table G3.A15, which
summarizes these studies, can be accessed at http://www.health.gov/paguidelines/report/.).
Rationale
Data From Observational, Epidemiological Studies
Several studies have shown that physical activity is associated with a significantly reduced
risk of GDM (200). These studies reported that increased levels of physical activity
(assessed by questionnaire) before pregnancy or during the first 20 weeks of pregnancy was
associated with reductions in risk of GDM. Overall the reduction in risk is about 50% when
active women are compared to inactive women.
Dose-Response Data
No RCTs have evaluated prospectively whether physical activity can prevent GDM or what
doses might be effective for such a response. Such trials would be of great value to establish
Physical Activity Guidelines Advisory Committee Report G3–28
Part G. Section 3: Metabolic Health
the role of exercise and physical activity in GDM. Available studies suggest that
approximately 30 minutes per day of moderate intensity physical activity is likely a
sufficient dose to decrease the GDM risk (200). However, this suggestion is based on
relatively few studies, and further studies should directly address the issue of dose-response.
Overall Summary and Conclusions
In summary, physical activity and exercise play a key role in preventing and treating
metabolic syndrome and T2D. The evidence for T2D are the clearest because RCTs have
been conducted to corroborate the findings of many observational trials, although, as
mentioned previously, 2 of the 3 RCTs combined physical activity and diet in their lifestyle
intervention. (The post-hoc findings on effects of physical activity in the absence of weight
change, although consistent and strong, are therefore not considerd strong RCT data but
rather are equivalent to the quality of prospective cohort study data.) The role of physical
activity and exercise in treating T1D is still being established. Current evidence suggests
that benefits are likely, perhaps most of all in the area of reducing mortality, CVD risk
factors, and microvascular complications. For both T1D and T2D, physical activity may
prevent the development of diabetic neuropathy and diabetic nephropathy. Finally, it appears
likely that physical activity and exercise may help prevent and treat gestational diabetes
although more research is needed to establish these findings. The amount of exercise that
appears to be the most well accepted and documented across the conditions included in this
section to date is 30 minutes of moderate physical activity 5 days per week. However, it is
clear that benefits are obtained with even lower volumes of physical activity. Walking is a
beneficial form of physical activity and has been especially well documented as effective in
T2D (where it has been most extensively studied). In the next section, the extensive research
needs for further study in the area of Metabolic Health are documented.
Research Needs
Although a considerable body of literature exists on the role of physical activity in
promoting and maintaining metabolic health, a number of questions remain unanswered and
require additional research:
• Available data indicate that regular physical activity is associated with reduced risk
of metabolic syndrome. However, it is not clear whether physical activity and
exercise can be used in treating or reversing metabolic syndrome, and additional
studies will help to clarify this issue.
• Research is needed in diverse populations to determine whether the effects of
physical activity across the range of metabolic health issues, including metabolic
syndrome, T2D, T1D, and gestational diabetes, differ with race and ethnicity.
Physical Activity Guidelines Advisory Committee Report G3–29
Part G. Section 3: Metabolic Health
• Further examination of the effects of physical activity on metabolic syndrome and
T2D also is warranted to determine whether and how its effect differ in youth and
adults.
• Additional research evaluating dose-response patterns of exercise in preventing
diabetes and cardiovascular outcomes in diabetes would make a valuable
contribution to the metabolic health literature.
• RCTs are needed to examine the effects of exercise on treating T1D in children and
adults. Good cardiovascular outcome data in response to physical activity in T1D is
lacking and could potentially be obtained in adult-onset T1D.
• Clinical studies in post-exercise hypoglycemia are needed to further study the
intermittent high-intensity exercise approach to prevention and to compare extra
carbohydrate versus lower insulin dosing approaches to treating T2D.
• Research is needed on several issues related to gestational diabetes. For example,
RCTs are needed to determine whether physical activity can prevent gestational
diabetes. It also would be useful to have additional dose-response data on the role of
exercise and physical activity in treating gestational diabetes.
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166. Kriska AM, LaPorte RE, Patrick SL, Kuller LH, Orchard TJ. The association of
physical activity and diabetic complications in individuals with insulin-dependent
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167. Orchard TJ, Dorman JS, Maser RE, Becker DJ, Ellis D, LaPorte RE, Kuller LH,
Wolfson SK, Jr., Drash AL. Factors associated with avoidance of severe
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168. Smith AG, Russell J, Feldman EL, Goldstein J, Peltier A, Smith S, Hamwi J, Pollari
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169. Colberg SR, Parson HK, Nunnold T, Holton DR, Swain DP, Vinik AI. Change in
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170. Colberg SR, Parson HK, Nunnold T, Herriott MT, Vinik AI. Effect of an 8-week
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171. Colberg SR, Stansberry KB, McNitt PM, Vinik AI. Chronic exercise is associated
with enhanced cutaneous blood flow in type 2 diabetes. J.Diabetes Complications
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172. Colberg SR, Parson HK, Holton DR, Nunnold T, Vinik AI. Cutaneous blood flow in
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173. Graham C, Lasko-McCarthey P. Exercise options for persons with diabetic
complications. Diabetes Educ. 1990 May;16(3):212-20.
174. Armstrong DG, Lavery LA, Holtz-Neiderer K, Mohler MJ, Wendel CS, Nixon BP,
Boulton AJ. Variability in activity may precede diabetic foot ulceration. Diabetes
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Physical Activity Guidelines Advisory Committee Report G3–46
Part G. Section 3: Metabolic Health
175. Lemaster JW, Reiber GE, Smith DG, Heagerty PJ, Wallace C. Daily weight-bearing
activity does not increase the risk of diabetic foot ulcers. Med.Sci.Sports Exerc. 2003
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176. Giacomozzi C, Caselli A, Macellari V, Giurato L, Lardieri L, Uccioli L. Walking
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177. Kanade RV, van Deursen RW, Harding K, Price P. Walking performance in people
with diabetic neuropathy: benefits and threats. Diabetologia 2006 Aug;49(8):1747-54.
178. Dingwell JB, Cusumano JP, Sternad D, Cavanagh PR. Slower speeds in patients with
diabetic neuropathy lead to improved local dynamic stability of continuous
overground walking. J.Biomech. 2000 Oct;33(10):1269-77.
179. Dingwell JB, Cavanagh PR. Increased variability of continuous overground walking
in neuropathic patients is only indirectly related to sensory loss. Gait.Posture. 2001
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180. Dingwell JB, Kang HG, Marin LC. The effects of sensory loss and walking speed on
the orbital dynamic stability of human walking. J.Biomech. 2007;40(8):1723-30.
181. Mueller MJ, Minor SD, Schaaf JA, Strube MJ, Sahrmann SA. Relationship of
plantar-flexor peak torque and dorsiflexion range of motion to kinetic variables
during walking. Phys.Ther. 1995 Aug;75(8):684-93.
182. Novak P, Burger H, Marincek C, Meh D. Influence of foot pain on walking ability of
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183. Wallberg-Henriksson H, Rincon J, Zierath JR. Exercise in the management of noninsulin-dependent diabetes mellitus. Sports Med. 1998 Jan;25(1):25-35.
184. Samanta A, Burden AC, Jagger C. A comparison of the clinical features and vascular
complications of diabetes between migrant Asians and Caucasians in Leicester, U.K.
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185. Hotta O, Taguma Y, Mitsuoka M, Takeshita K, Takahashi H. Urinary albumin
excretion in patients with non-insulin-dependent diabetes mellitus in an early
microalbuminuric stage. Nephron 1991;58(1):23-6.
186. Garg SK, Chase HP, Shapiro H, Harris S, Osberg IM. Exercise versus overnight
albumin excretion rates in subjects with type 1 diabetes. Diabetes Res.Clin.Pract.
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Physical Activity Guidelines Advisory Committee Report G3–47
Part G. Section 3: Metabolic Health
187. Groop L, Stenman S, Groop PH, Makipernaa A, Teppo AM. The effect of exercise on
urinary excretion of different size proteins in patients with insulin-dependent diabetes
mellitus. Scand.J.Clin.Lab Invest 1990 Sep;50(5):525-32.
188. Matsuoka K, Nakao T, Atsumi Y, Takekoshi H. Exercise regimen for patients with
diabetic nephropathy. J.Diabet.Complications 1991 Apr;5(2-3):98-100.
189. Morgensen CE. Nephropathy: early. In: Ruderman N, Devlin JT, Schneider SH, et al.,
editors. Handbook of Exercise in Diabetes. Alexandria, VA: American Diabetes
Association; 2002. p. 433-49.
190. Fredrickson SK, Ferro TJ, Schutrumpf AC. Disappearance of microalbuminuria in a
patient with type 2 diabetes and the metabolic syndrome in the setting of an intense
exercise and dietary program with sustained weight reduction. Diabetes Care 2004
Jul;27(7):1754-5.
191. Lazarevic G, Antic S, Vlahovic P, Djordjevic V, Zvezdanovic L, Stefanovic V.
Effects of aerobic exercise on microalbuminuria and enzymuria in type 2 diabetic
patients. Ren Fail. 2007;29(2):199-205.
192. Cruickshanks KJ, Moss SE, Klein R, Klein BE. Physical activity and the risk of
progression of retinopathy or the development of proliferative retinopathy.
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193. Cruickshanks KJ, Moss SE, Klein R, Klein BE. Physical activity and proliferative
retinopathy in people diagnosed with diabetes before age 30 yr. Diabetes Care 1992
Oct;15(10):1267-72.
194. LaPorte RE, Dorman JS, Tajima N, Cruickshanks KJ, Orchard TJ, Cavender DE,
Becker DJ, Drash AL. Pittsburgh Insulin-Dependent Diabetes Mellitus Morbidity and
Mortality Study: physical activity and diabetic complications. Pediatrics 1986
Dec;78(6):1027-33.
195. Anderson B, Jr. Activity and diabetic vitreous hemorrhages. Ophthalmology 1980
Mar;87(3):173-5.
196. Bernbaum M, Albert SG, Cohen JD, Drimmer A. Cardiovascular conditioning in
individuals with diabetic retinopathy. Diabetes Care 1989 Nov;12(10):740-2.
197. Albert SG, Bernbaum M. Exercise for patients with diabetic retinopathy. Diabetes
Care 1995 Jan;18(1):130-2.
198. Stevens RJ, Kothari V, Adler AI, Stratton IM. The UKPDS risk engine: a model for
the risk of coronary heart disease in Type II diabetes (UKPDS 56). Clin.Sci.(Lond)
2001 Dec;101(6):671-9.
Physical Activity Guidelines Advisory Committee Report G3–48
Part G. Section 3: Metabolic Health
199. Summary of revisions for the 2006 Clinical Practice Recommendations. Diabetes
Care 2006 Jan;29 Suppl 1:S3.
200. Dempsey JC, Butler CL, Williams MA. No need for a pregnant pause: physical
activity may reduce the occurrence of gestational diabetes mellitus and preeclampsia.
Exerc.Sport Sci.Rev. 2005 Jul;33(3):141-9.
201. Getahun D, Nath C, Ananth CV, Chavez MR, Smulian JC. Gestational diabetes in the
United States: temporal trends 1989 through 2004. Am.J.Obstet.Gynecol. 2008 Feb
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202. Linne Y. Effects of obesity on women's reproduction and complications during
pregnancy. Obes.Rev. 2004 Aug;5(3):137-43.
203. Kelly C, Booth GL. Diabetes in Canadian Women. BMC.Womens Health 2004 Aug
25;4 Suppl 1:S16.
204. Jovanovic L. What is so bad about a big baby? Diabetes Care 2001 Aug;24(8):13178.
205. Schaefer-Graf UM, Kleinwechter H. Diagnosis and new approaches in the therapy of
gestational diabetes mellitus. Curr.Diabetes Rev. 2006 Aug;2(3):343-52.
Physical Activity Guidelines Advisory Committee Report G3–49
Part G. Section 4:
Energy Balance
Introduction
Overweight and obesity are linked to increased risk of morbidity from hypertension,
dyslipidemia, type 2 diabetes, coronary heart disease, stroke, gallbladder disease,
osteoarthritis, sleep apnea and respiratory problems, and endometrial, postmenopausal
breast, prostate, and other cancers (1;2). In addition, obesity is associated with excess overall
mortality (3). Unfortunately, the prevalence of overweight and obesity has increased
dramatically over the past 20 years in the United States to 70.8% and 31.1% for adult men,
and 61.8% and 33.2% for adult women, respectively (4). This increase has been attributed to
changes in environment and lifestyle factors because the escalating prevalence has been
occurring in a constant genetic milieu. The focus in this chapter is on the role that physical
activity plays in energy balance.
Review of the Science
Overview of Questions Addressed
This chapter addresses 5 major questions related to physical activity and energy balance.
1. How much physical activity is needed for weight stability and weight loss?
2. How much physical activity is needed to prevent weight regain in previously
overweight individuals?
3. What is the effect of physical activity on body composition parameters (e.g., waist
circumference, intra-abdominal fat, abdominal obesity, total body fat) that are related
specifically to metabolic disorders?
4. What effects do sex and age have on the role of physical activity in energy balance?
5. How do the physical activity requirements for weight maintenance differ across
racial/ethnic and socioeconomic groups?
Data Sources and Process Used to Answer Questions
The Energy Balance subcommittee used the Physical Activity Guidelines for Americans
Scientific Database as its primary source for each question (see Part F. Scientific Literature
Search Methodology, for a complete description of the Database). It also used other
Physical Activity Guidelines Advisory Committee Report G4–1
Part G. Section 4: Energy Balance
databases, reviews, and meta-analyses to obtain evidence bearing on each question. Specific
search strategies are described for each question.
Caveats
Four points need to be mentioned at the outset of this chapter on physical activity and
energy balance. First, in contrast to outcomes addressed in other chapters, in which physical
activity can be discussed as the primary variable affecting the outcome, achieving energy
balance is dependent on both energy intake and energy expenditure. With the availability of
inexpensive and easily accessed high-calorie, highly palatable foods, it is far easier to
increase energy intake than to increase energy expenditure in our society. In support, the
2005 Dietary Guidelines Advisory Committee Report (5) indicated that most Americans are
consuming energy in excess of energy needs, and it is not likely to change in the near future.
Consequently, final recommendations related to the level of physical activity needed for
weight maintenance, weight loss, or prevention of weight regain after weight loss must
consider energy intake issues as well.
Second, when a caloric deficit induced by exercise is compared with an equivalent caloric
deficit created by a reduction in caloric intake, there is little or no difference in weight loss
(6). However, in many weight loss studies, the proportion of the caloric deficit due to
physical activity is only a small fraction of the overall caloric deficit, and consequently, the
contribution that physical activity makes to weight loss is relatively small. This must be
remembered as we address the role of physical activity alone on weight-related issues.
Third, secular trends have increased the use of automation and labor-saving devices on the
job, at home and in the community and increased passive leisure-time physical activity (e.g.,
TV/VCR, computer use). These trends influence the amount of physical activity needed to
achieve energy balance.
Finally, if we did not have an overweight and obesity problem in our society, we would still
need a physical activity recommendation to maintain health and prevent disease. That simple
message is lost on many who focus solely on the role of physical activity in preventing
overweight and obesity. Consequently, the level of physical activity needed to maintain
health and prevent disease is the baseline for any physical activity recommendation for
energy balance.
Question 1: How Much Physical Activity Is Needed for Weight
Stability and Weight Loss?
Conclusions
All study designs provide clear evidence of a dose-response relation between physical
activity and weight loss. However, few data are available on weight stability over the long
term. Available data on weight stability are from short-term clinical trials. Based on these
Physical Activity Guidelines Advisory Committee Report G4–2
Part G. Section 4: Energy Balance
trials, a dose of physical activity in the range of 13 to 26 MET-hours per week resulted in a
modest 1% to 3% weight loss, consistent with weight stability over time (7-9). Thirteen
MET-hours per week is equivalent to walking at a 4 mile per hour pace for 150 minutes per
week or jogging at a 6 mile per hour pace for 75 minutes per week. The magnitude of weight
loss resulting from studies of resistance exercise is typically less than 1 kilogram
(2.2 pounds). However, this result may be affected by the relatively short duration of these
studies and gains in fat-free mass that accompany such interventions. In contrast, it is clear
that if one wants to achieve weight loss (i.e., more than 5% decrease in body weight), a
dietary intervention also is needed. The dietary intervention could include either a
maintenance of baseline caloric intake, or a reduction in caloric intake to accompany the
physical activity intervention. The magnitude of change in weight due to physical activity is
additive to that associated with caloric restriction.
Definitions
To aid in the study of patterns of weight change, the scientific literature has operationally
defined the concept of weight stability. St. Jeor and colleagues (10) define weight stability
as a change of 2.3 kilograms (5 pounds) or less of initial body weight. In this study,
participants’ weights were monitored over a period of time using this criterion. It was
determined that 62%, 52%, 49%, and 46% of participants were classified as maintaining
their body weight at 1, 2, 3, and 4 years of follow-up, respectively. The Pound of Prevention
Study also defined weight maintenance as a change of 2.3 kilograms (5 pounds) or less (11)
of initial body weight. When examined over a 3-year period, 40% of men and 38% of
women were classified as “maintainers,” with a mean weight change of 0.3 kilograms
(0.7 pounds) and 0.2 kilograms (0.4 pounds), respectively. Moreover, across the entire
sample of 957 individuals, the mean weight gain over a 3-year period was 1.7 kilograms
(3.7 pounds) for men and 1.8 kilograms (4 pounds) for women. This would suggest that the
mean weight gain across the population may be approximately 0.6 kilograms (1.3 pounds)
per year.
More recently, Stevens and colleagues (12) have recommended that weight maintenance be
defined as less than a 3% change in body weight. Moreover, they recommended that a
change in body weight of 3% to less than 5% of initial weight be considered as small
fluctuations in body weight, and a change of 5% or more of body weight be considered
clinically significant. Considering these standards, an obese individual weighing
91 kilograms (200 pounds) would need to reduce body weight by 4.5 kilograms (10 pounds)
to have a significant weight loss, and a weight change of 2.7 kilograms (6 pounds) would be
considered weight stability. These standards should be considered when evaluating the
effect of physical activity on body weight change to determine whether various doses and
modes of physical activity result in weight stability or clinically relevant weight loss.
Physical Activity Guidelines Advisory Committee Report G4–3
Part G. Section 4: Energy Balance
Rationale
A search of the Physical Activity Guidelines for Americans Scientific Database identified
126 research articles on the effect of physical activity on weight loss and weight stability.
Additionally, pertinent reviews available through a MEDLINE search were considered.
Cross-Sectional Studies
Twenty-four cross-sectional studies were identified that examined the association between
physical activity and body weight. Of these 24 studies, 23 reported results suggesting an
inverse relationship between physical activity and body weight and/or body mass index
(BMI) (13-35). These studies tended to illustrate a dose-response relationship between
physical activity and body weight or BMI. For example, Giovannucci and colleagues (14)
reported that when 0.9, 4.8, 11.3, 22.6, and 46.8 MET-hours per week were used to define
quintiles of physical activity, corresponding BMI values were 25.4, 25.3, 25.1, 24.7, and
24.4 kg/m2, respectively. More recently, Kavouras and colleagues (15) reported that
individuals participating in physical activity that is consistent with the current consensus
public health recommendations of at least 30 minutes per day on 5 days a week had a
significantly lower BMI (25.9 kg/m2) when compared to the BMI (26.7 kg/m2) of less active
individuals (Figure G4.1). Thus, based on these findings, it appears that levels of physical
activity that are consistent with a range of 30 to 60 minutes per day on at least 5 days per
week (150 to 300 minutes per week) is sufficient to maintain and/or significantly reduce
body weight.
Prospective Studies
Nine prospective studies were identified that reported on the benefits of physical activity to
prevent weight gain and/or result in weight loss (36-44). Three studies, which had a
follow-up period of 1 to 3 years, all reported a favorable association between physical
activity and weight-related outcomes (36;37;39). The remaining 6 studies, which had a
follow-up period of 6.5 years or greater, also reported a favorable association between
physical activity and weight-related outcomes (38;40-44). Berk and colleagues (43) found
that individuals who initially reported less than 60 minutes per week of physical activity and
increased to 134 minutes per week of physical activity had an increase in BMI of 0.4 kg/m2
across a 16-year follow-up period, but this was not significantly different from the 0.9kg/m2
increase observed for individuals who remained sedentary (less than 60 minutes per week) at
both assessment periods. These data suggest that less than 150 minutes per week of physical
activity will result in a non-significant blunting of weight gain compared to individuals who
remain sedentary. However, individuals who were classified as active at both assessment
periods were participating in 261 minutes per week of physical activity, and had a
significantly smaller change in BMI compared to individuals who were initially active
(more than 60 minutes per week) at baseline but became inactive at follow-up (less than
60 minutes per week). This supports the need to maintain a physically activity lifestyle to
manage body weight long-term.
Physical Activity Guidelines Advisory Committee Report G4–4
Part G. Section 4: Energy Balance
Figure G4.1. Differences in Body Mass Index Due to Level of Physical Activity
25.4
25.6
25.8
26.0
26.2
26.4
26.6
26.8
B
od y M
as s In de x (B
M
I)
Less Active Active*
*Active is defined as the consensus public health recommendation for physical activity (3 or more days per week of
20 minutes per day at vigorous intensity or 5 or more days per week of 30 minutes per day at moderate intensity).
Source: Adapted from Kavouras and colleagues, 2007 (15).
Figure G4.1. Data Points
Less Active Active*
BMI 26.7 25.9
Randomized Trials
Endurance Exercise
Twenty studies were identified that examined the effect of endurance exercise on body
weight. However, 7 studies were not reviewed due to the intent of the study to focus on
marathon training, a dietary intervention to counter or enhance the weight loss effects of
exercise, the inclusion of only subjects with serious psychiatric disabilities, the lack of a
consistent training paradigm across the observation period, or the exercise volume not
expressed in as minutes per week. The remaining 13 studies were reviewed in greater detail.
Twelve used a randomized design, although 3 of them did not have a control group and/or
the physical activity was in addition to a dietary intervention (45-47), and 1 used a
non-randomized design to examine the effect of physical activity but did not include a
comparison group (48). In addition, the primary purpose of 5 of the studies was on
Physical Activity Guidelines Advisory Committee Report G4–5
Part G. Section 4: Energy Balance
something other than weight loss (49-53). The remaining 4 studies (7-9;54) had sufficient
statistical power to evaluate the effect of physical activity on body weight and body
composition.
These studies ranged in duration from 8 to 16 months, and physical activity level ranged
from 180 minutes of moderate-intensity physical activity per week to 360 minutes of
moderate- to vigorous-intensity physical activity per week. In addition, one study (9)
evaluated 3 levels of physical activity, and 2 (7;8) established, post hoc, tertiles of physical
activity participation (adherence) based on activity logs and/or pedometer records to
evaluate a dose-response pattern. Typical weight losses were 1 to 3 kilograms (2.2 to
6.6 pounds), which corresponded to less than 3% change in body weight, but evidence of a
dose-response relationship was clear, with those doing the greatest amount of physical
activity achieving weight losses of 4% to 6% (the latter associated with an energy
expenditure of 668 kcal per session, 5 days per week). A dose of physical activity in the
range of 13 to 26 MET-hours per week resulted in a modest 1% to 3% weight loss,
consistent with weight stability over time.
Resistance Exercise
An alternative form of physical activity is resistance exercise. Ten studies were reviewed
that examined the impact of this form of exercise on change in body weight, and all of these
studies showed a modest reduction (less than 1 kilogram) or a non-significant change in
body weight (55-64). This finding of a modest impact of resistance exercise on body weight
was confirmed in a literature review (65). A potential explanation for this lack of a reduction
in body weight is that many of these studies reported an increase in fat-free mass resulting
from resistance exercise training, which resulted in a reduction in percent body fat, but did
not change absolute body weight or fat mass. Thus, changes in body composition may be a
desirable outcome to examine when determining the effect of resistance exercise on body
weight parameters. However, the lack of a sufficient dose of physical activity to elicit a
significant energy deficit may also explain these findings, as many of these studies were
relatively short in duration and included only 2 to 3 days per week of resistance exercise.
Five studies from the Physical Activity Guidelines for Americans Scientific Database
examined the combination of endurance and resistance exercise on change in body weight.
Two studies used randomized designs to assign participants to a physical activity group or a
control group (66;67), 1 used a randomized cross-over design involving 8 weeks of physical
activity and 8 weeks of no physical activity (68), and 2 examined the effect of physical
activity but did not include a control group (69;70). Four of these studies reported no effect
of combined endurance plus resistance exercise on change in body weight (66-69), and
1 study that did not include a control group (70) reported a significant effect. A potential
limitation of these studies is that they ranged from 8 to 10 weeks in duration, which may
have been too short a time to significantly affect body weight.
Physical Activity Guidelines Advisory Committee Report G4–6
Part G. Section 4: Energy Balance
In general, regular participation in moderate-to-vigorous physical activity is associated with
weight maintenance over time. In contrast, it is clear that if one wants to achieve clinically
relevant weight loss (a decrease of 5% or more in body weight), a dietary intervention is
usually needed. This is shown clearly in Figure G4.2, adapted from Wing, 1999 (71).
Figure G4.2. Weight Loss Related to a Diet Intervention, an Exercise Intervention,
and a Diet + Exercise Intervention
-12.0
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
W
ei gh t L
os s (k g) 0 Months 6 Months
Diet Exercise Diet + Exercise
Source: Adapted from Wing, 1999 (71)
Figure G4.2. Data Points—Weight Loss in kg
0 Months 6 Months
Diet 0 -9.1
Exercise 0 -2.1
Diet + Exercise 0 -10.3
The magnitude of weight loss due to physical activity is additive to caloric restriction, but
physical activity is generally insufficient by itself to bring about clinically significant weight
loss. Consistent with this, McTiernan and colleagues (8) estimated that the physical activity
intervention in their study should have produced a weight loss of 7.8 kilograms, rather than
the 1.4 kilograms (women) and 1.8 kilograms (men) observed, if caloric intake had
remained stable. Further, studies in which the caloric intake was held constant (by design)
from baseline showed that the weight loss associated with the physical activity intervention
Physical Activity Guidelines Advisory Committee Report G4–7
Part G. Section 4: Energy Balance
was what one would predict from the physical activity energy expenditure (6).
Consequently, the addition of a dietary restraint to not increase caloric intake may have
resulted in clinically significant weight loss, rather than just weight stability with the
physical activity intervention mentioned above. The magnitude of weight loss reported in
these studies is consistent with earlier reviews on this topic by Wing (71) and the Expert
Panel of Clinical Guidelines for the Treatment of Obesity (1).
Question 2. How Much Physical Activity Is Needed to Prevent
Weight Regain in Previously Overweight Individuals?
Conclusions
Most of the available literature indicates that “more is better” when it comes to the amount
of physical activity needed to prevent weight regain following weight loss. However, the
literature has some considerable shortcomings regarding the appropriate research design
needed to directly address this question. Given these limitations, the estimated gross energy
expenditure needed to achieve weight maintenance following substantial weight loss is
about 31 kilocalories per kilogram week or 4.4 kcal·kg-1·d-1, which is equivalent to walking
54 minutes per day at a 4 mile per hour pace, walking 80 minutes per day at a 3 mile per
hour pace, or jogging 26 minutes per day at a 6 mile per hour pace (72-74).
Rationale
Initial references were obtained with a search of the Physical Activity Guidelines for
Americans Scientific Database. Key words included adults, exercise, physical activity,
obesity, adiposity, weight, and BMI. Eight systematic reviews or meta-analyses also were
reviewed for pertinent references. Studies that investigated special populations (e.g.,
physically disabled), included individuals with a disease known to affect weight (e.g.,
cancer), or weight loss drugs, were excluded. To be included, studies had to target a period
of weight loss followed by a period of weight maintenance using physical activity as the
strategy for preventing weight regain.
Eight randomized trials met the above criteria and were used for this review. Of the eight
studies, only three had a design in which participants were randomized after weight loss and
only two used a control group. Three observational or prospective cohort studies were
identified that met the above criteria and were used for this review. Four position papers or
reports also were used as references.
It is generally accepted that individuals can lose weight but most cannot maintain significant
weight loss. Because it has an energy equivalent, physical activity is universally promoted as
a necessary component of strategies to maintain weight loss (1;75;76). Indeed, physical
activity is often cited as the best predictor of weight maintenance after weight loss (77;78).
A systematic review of physical activity to prevent weight regain subsequent to weight loss
was completed by Fogelholm and Kukkonen-Harjula (79). The majority of studies included
Physical Activity Guidelines Advisory Committee Report G4–8
Part G. Section 4: Energy Balance
in this review were observational studies and studies of individuals who were randomized at
baseline to exercise or no exercise, or to different levels of physical activity. Follow-up
varied from several months to several years and generally showed that individuals who
engaged in exercise experienced less regain than those individuals who did not, and those
individuals who engaged in greater amounts of physical activity experienced less regain than
those who did more moderate levels. Only 3 studies used a design in which individuals were
randomized to physical activity after weight loss (80-82), and the results were inconsistent,
showing that physical activity had an indifferent, negative, or positive effect on prevention
of weight regain.
Despite the accepted concept that physical activity is necessary for successful weight
maintenance after weight loss, the amount that is needed remains uncertain. The 1995
Centers for Disease Control/American College of Sports Medicine (CDC/ACSM)
recommendations for physical activity specified the accumulation of 30 minutes of
moderate-intensity physical activity for most days of the week (83). These guidelines were
provided for health promotion and disease prevention. However, they were widely
interpreted to also be useful for weight management. Minimum levels of 150 minutes per
week (30 minutes per day, 5 days a week) of moderate-intensity physical activity were also
recommended by the ACSM Position Stand for “Appropriate Intervention Strategies for
Weight Loss and Prevention of Weight Regain for Adults” (75). However, recent evidence
suggests that greater levels of physical activity may be necessary to prevent weight regain
after weight loss. For example, individuals in the National Weight Control Registry who
have maintained weight loss have shown levels of energy expenditure equivalent to walking
about 28 miles a week (77). Schoeller and colleagues (74) used doubly-labeled water to
study women who recently lost 23±9 kilograms of weight in order to estimate the energy
expenditure needed to prevent weight regain. Retrospective analyses of these data were
performed to determine the level of physical activity that provided maximum differentiation
between gainers and maintainers. Based on these analyses, it was determined that
individuals would need to expend about 4.4 kilocalories per kilogram per day in physical
activity (which is equivalent to about 80 minutes per day of moderate-intensity physical
activity or 35 minutes per day of vigorous physical activity) to prevent weight regain.
Jakicic and colleagues (73;84) and Andersen and colleagues (85) provided data from
randomized trials showing that individuals who performed large amounts of physical
activity maintained weight loss better at follow-up of 18 months, 12 months, and 12 months,
respectively, than did those doing smaller amounts of physical activity. In particular, Jakicic
and colleagues (73;84) showed very little weight regain in individuals who performed more
than 200 minutes per week of moderate-intensity physical activity. Ewbank and colleagues
(72) also found similar results 2 years after weight loss by very-low-energy diet.
Retrospectively grouping participants by levels of self-reported physical activity, individuals
who reported greater levels (i.e., walking about 16 miles per week,) had significantly less
weight regain than individuals reporting less physical activity per week (4.8 to 9.1 miles per
week). However, it is important to note that individuals in all 3 studies above were grouped
into physical activity categories retrospectively and were not randomly assigned to those
Physical Activity Guidelines Advisory Committee Report G4–9
Part G. Section 4: Energy Balance
groups after weight loss. Thus, the amount of physical activity was self-selected and
therefore does not provide clear evidence for the amount needed to prevent weight regain.
To explore the effects of levels of physical activity greater than those normally
recommended in weight management programs, Jeffery and colleagues (86), targeted energy
expenditures of 1,000 kilocalories per week and 2,500 kilocalories week for 18 months in
2 groups of participants; these levels were randomly assigned at baseline. The actual
reported energy expenditure at 18 months was 1,629 ± 1,483 and 2,317 ± 1,854 kilocalories
per week for the 1,000 and 2,500 kilocalories per week groups, respectively. At 6 months,
weight loss did not differ between the groups, but there were significant differences at
12 and 18 months (weight maintenance) follow-up, with the 2,500 kilocalories per week
group showing significantly greater weight losses (6.7 ± 8.1 kilograms versus 4.1 ±
8.3 kilograms). The energy equivalent for walking for the 2,500 kilocalories per week group
and 1,000 kilocalories per week group was about 3.3 miles per day and about 2.3 miles day,
respectively. This study showed that greater levels of physical activity resulted in
significantly lower levels of weight regain. However, the results must be interpreted with
caution, as the percentage of individuals meeting the targeted energy expenditure varied
greatly, and the behavioral interventions were not equal.
In general, large volumes of physical activity are needed to prevent weight regain in those
who have lost a great deal of weight. Studies by Ewbank and colleagues (72), Jakicic and
colleagues (73), and Schoeller and colleagues (74) indicate that the volume of physical
activity needed for that purpose is approximately 31 MET-hours per week or 4.4 MET-hours
per day.
Question 3. What Is the Effect of Physical Activity on Body
Composition Parameters (e.g., Waist Circumference,
Intra-Abdominal Fat, Abdominal Adiposity, Total Body Fat)
That Are Specifically Related to Metabolic Disorders?
Conclusions
A dose-response relation exists between volume of physical activity and decreases in total
and abdominal adiposity in overweight and obese individuals. In the absence of coincident
caloric restriction, aerobic physical activity in the range of 13 to 26 MET-hours per week
results in decreases in total and abdominal adiposity that are consistent with improved
metabolic function. Thirteen MET-hours per week is equivalent to walking at a 4 mile per
hour pace for 150 minutes per week or jogging at a 6 mile per hour pace for 75 minutes per
week (7-9). However, larger volumes of physical activity (e.g., 42 MET-hours per week)
result in decreases in intra-abdominal adipose tissue that are 3 to 4 times those seen with
13 to 26 MET-hours per week, even without weight loss. The evidence thus far suggests that
abdominal fat loss with increased physical activity is proportional to overall fat loss.
Physical Activity Guidelines Advisory Committee Report G4–10
Part G. Section 4: Energy Balance
Definitions
The obesity phenotype that conveys the greatest health risk of metabolic disorders, such as
the metabolic syndrome and type 2 diabetes, is one that favors an accumulation of adipose
tissue in the abdominal region. Regular physical activity is recognized as an effective
method of preventing excessive weight and fat gain throughout adulthood, and although
physical activity is commonly prescribed to reduce overall obesity, the influence of
exercise-induced weight loss on abdominal adiposity is not clear. Abdominal adiposity is
characterized several ways in the scientific literature. Modern imaging techniques such as
MRI, DXA, and CT provide highly-precise quantification of total body fat content
(expressed in relative [%] or absolute [kilogram] terms), as well as specific measures of
abdominal fat, such as the subcutaneous and visceral (intra-abdominal) fat areas (cm2).
Although less precise than the imaging measures, the waist circumference (measured in
centimeters and usually defined at the level of the lowest rib) is the most widely-used
anthropometric measure of abdominal adiposity and therefore has the most clinical utility of
all these measures.
Rationale
The Physical Activity Guidelines for Americans Scientific Database was accessed using the
following delineation terms: 1) population sub-group: adults/older adults; 2) study design:
randomized controlled trials (RCTs); longitudinal experimental studies (before/after); and
prospective observational studies; and 3) health outcomes: adiposity measures (e.g., total
fat, percent fat, abdominal fat area [visceral and subcutaneous], waist circumference) related
specifically to metabolic disorders. Evidence obtained using the Scientific Database was
supplemented with recently-published scientific papers and review articles.
Favorable body composition changes (reduced fat mass and increased lean mass) occur with
the adoption of regular physical activity — even among individuals aged 75 years and older,
and evidence suggests that current activity is more protective than past activity (87;88).
What is not clear at this time is the amount and type of activity necessary to result in
meaningful alterations in abdominal fat, which in turn can preserve or improve metabolic
function. Unfortunately, few large-scale RCTs have been directed toward this question. The
data that do exist are from relatively small RCTs and controlled intervention studies.
Nonetheless, these studies paint a consistent picture of energy expenditure requirements for
minimizing fat gain and/or reducing excess total and abdominal fat.
Several RCTs and controlled interventions report the benefits of moderate- to vigorousintensity aerobic exercise to overall improvements in body weight, body fat, and lean mass
in middle-aged and older adults (7;8;89-93). The data are equivocal, however, with regard to
the ability to significantly alter regional distribution of body fat with endurance training (79;54;91;93-95). In general, aerobic exercise, without dieting, appears to have a beneficial
effect on overall and abdominal adiposity. However, the exercise dose necessary to result in
these alterations is rather high. In Irwin and colleagues (7), 176 minutes per week of
moderate- to vigorous-intensity physical activity performed over 12 months resulted in a
Physical Activity Guidelines Advisory Committee Report G4–11
Part G. Section 4: Energy Balance
reduction in subcutaneous fat and intra-abdominal fat of 5.4% and 5.8%, respectively, with
the impact being even larger when contrasted with the control group. In addition, McTiernan
and colleagues (8) used a higher volume/longer duration aerobic exercise regimen
(60 minutes or more of moderate- to vigorous-intensity physical activity on 6 days per
week) over 12 months of training and also reported modest decreases in the subcutaneous
abdominal fat (5% in women and 11% in men) and intra-abdominal fat (6% in women and
8% in men) depots and in the waist circumference (2% in women and 3% in men). Data
from the Studies of Targeted Risk Reduction Interventions through Defined Exercise
(STRRIDE) show that the highest amount of exercise performed (equivalent of jogging
approximately 20 miles per week) over 8 months resulted in, at best, a 7% decrease in
visceral and subcutaneous fat in men and women aged 40 to 65 years (9). Ross and
colleagues (93) report an 18% reduction in total fat and a 20% reduction in abdominal fat
among non-dieting abdominally-obese women who exercised every day for about
60 minutes (or 500 kilocalorie expenditure) for 14 weeks. Together, these findings (7-9;93)
and others (6) support the contention that in the absence of coincident caloric restriction,
aerobic physical activity in the range of 13 to 26 kilocalories per kilogram per week results
in decreases in total and abdominal adiposity that are consistent with improved metabolic
function. However, as mentioned above, when more physical activity is done per week (e.g.,
42 MET-hours per week), decreases in intra-abdominal adipose tissue approach 3 to 4 times
the level seen with 13 to 26 MET-hours per week, even without weight loss (93).
A recent study employing 45 minutes of resistance exercise training twice weekly also
reports small, yet favorable changes in total and abdominal fat (56) in middle-age and older
adults, but not in younger, non-obese women (96). In a 2-year study of resistance training in
overweight and obese premenopausal women, Schmitz and colleagues (56) report a 4%
decrease in total fat in the exercise group versus a negligible change in the control group
(P<0.01). Interestingly, intra-abdominal fat increased over 2 years by 7% in the exercise
group and by 21% in the control group, underscoring the benefits of resistance training
(without caloric restriction) in at least minimizing intra-abdominal fat gain in middle-aged
women. The benefits of resistance training may be most noticeable among obese and older
populations, who typically have the greatest amount of abdominal fat.
Generally, short-term (less than 6 months) exercise interventions will have a positive effect
on body composition. However, the magnitude of these alterations in body fat or lean mass
may be of limited biological significance (48). Studies that employ moderate- to vigorousintensity aerobic exercise of at least 55-75% VO2peak (4.5-6 METs), on most days of the
week (i.e., 4 or more days), over intervention periods of at least 9 months, report the most
significant changes in body composition (7-9;91;93). In general, the amount of adiposity
present in study subjects at baseline will affect the amount of fat lost with a given
intervention. Indeed, studies employing overweight or obese subjects (7;8;56;92;93) report
greater improvements in body composition than those studies using subjects of normal
weight (48;96). Also important is the dose-response relation highlighted by Ross and
colleagues (93) between exercise-induced weight loss and fat loss — that is, greater total
weight loss will result in greater fat loss (7;93). Nonetheless, Ross and colleagues (93)
Physical Activity Guidelines Advisory Committee Report G4–12
Part G. Section 4: Energy Balance
report that, even without coincident weight loss, 60 minutes per day of vigorous-intensity
exercise (approximately 500 kilocalories per day) on 7 days per week still resulted in
statistically significant reductions in total (7%), abdominal (10%), and intra-abdominal
(18%) fat in abdominally-obese premenopausal women.
Overall, regular participation in aerobic physical activity causes decreases in both total and
abdominal adiposity, changes that are consistent with improved metabolic function. The
greater the volume of physical activity, the larger the change in adiposity.
Question 4: What Effects Do Sex and Age Have on the Role of
Physical Activity in Energy Balance?
Conclusions
Some evidence indicates that the amount of physical activity needed to maintain a constant
weight differs between men and women and increases with age. This may be due to a
number of physiologic and behavioral factors that also vary by sex and by age. However, the
evidence is not sufficient to recommend differential physical activity prescriptions based on
sex or on age alone.
Rationale
The Physical Activity Guidelines for Americans Scientific Database was accessed using the
following delineation terms: 1) population sub-group: adults/older adults; 2) study design:
randomized controlled trials, longitudinal experimental studies (before/after), prospective
observational studies, and cross-sectional studies; 3) health outcomes: body weight; and
4) search term: aging, age, gender, men, women. Studies identified using the Scientific
Database were supplemented by recently-published or in press scientific papers and review
articles. Findings presented here were limited to studies having a forward study design (i.e.,
prospective observational and/or longitudinal experimental studies) with adequate statistical
power to distinguish moderate effect sizes from chance alone.
Sex
The prevalence of obesity is higher among women compared with men, particularly among
women from ethnic minority groups (4;97). Although women report less physical activity
than men, it is not clear whether this is actually so, or whether it is a consequence of
measurement error resulting from the low sensitivity of traditional physical activity surveys
(83;98;99). In any case, potential sex differences in the influence of physical activity on
weight stability are important to consider in maximizing the utility of future public health
guidelines.
Cross-sectional and longitudinal epidemiologic studies generally have demonstrated
inverse associations between physical activity and weight gain in both men and women
(e.g., 100-105). Dose-response relationships have been somewhat less consistent in women
Physical Activity Guidelines Advisory Committee Report G4–13
Part G. Section 4: Energy Balance
than in men. However, as stated previously, this may be attributable to measurement error
associated with self-reported data (100;106). Indeed, objective measurements of energy
expenditure (e.g., doubly-labeled water) have either stronger inverse associations in men
than in women or no biological sex differences in response to different amounts of physical
activity (107). The few intervention studies that included both men and women (along with
sex-specific analyses) report weight or fat losses only in men (107), no change in either sex
(67), or similar changes in both men and women (e.g., 8;58;89;108;109).
It is likely that differences in findings among these intervention studies reflect dissimilarities
among study protocols. However, even within particular study samples, observed sex
differences in weight loss responses to exercise can be attributed to a number of factors. For
instance, several highly controlled laboratory-based intervention studies have noted that
women are more resistant to weight loss or may require greater energy expenditure
compared with men to maintain a healthy body weight (54;100;107). Indeed, this suggests
that a similar absolute energy expenditure (e.g., 1,200 kilocalories per week) may not yield
the same results in men and women. This may be due to a greater proportion of less
lipolytically responsive gluteofemoral adipose tissue in younger and middle-aged women
than in men of the same age. Animal studies also have observed a sex dimorphism in the
control of energy homeostasis that might be attributed to a differential interaction between
adiposity hormones and food intake control systems in the brain (110;111). These biological
sex differences in responsiveness to weight change may be difficult to discern in large
community-based interventions or at the population level, however, due to measured or
unmeasured sex differences in: 1) how a similar level of physical activity is performed
(walking vs. water aerobics vs. running); 2) adherence to a given exercise prescription; or 3)
dietary intake. Because a number of other physiological (body mass, peak aerobic capacity)
or behavioral factors (cigarette smoking, drinking, hormone replacement therapy) also may
vary between men and women, studies that measure sex differences in weight loss responses
to exercise must be careful to control for these covariables either by matching in
experimental designs or by appropriate statistical adjustments when feasible.
Age
Because the risk of chronic disease increases markedly with sedentary lifestyles and with
age, the public health burden associated with inactivity is substantial among middle-aged
and older adults (88). In general, lower levels of physical activity are associated with higher
body weight and body fat in middle-aged and older adults (4;87;112-114). The
epidemiologic studies to date provide clear longitudinal evidence linking habitual physical
activity to the prevention of excess weight gain in both men and women (100-105;115) and
this is true even in older age. Although the effect sizes from these observational studies
appear small, over the lifespan these small savings in excess weight gain accumulate into net
savings that are quite meaningful with regard to minimizing the risk of obesity-related
disorders. Moreover, the longitudinal epidemiologic evidence suggests that as people
progress from young adulthood to old age, they require increasing amounts of daily energy
expenditure to maintain a constant body weight (37;104;105;115). More than likely, this is
due to a combination of physiologic (e.g., sex hormone depletion, decline in peak aerobic
Physical Activity Guidelines Advisory Committee Report G4–14
Part G. Section 4: Energy Balance
capacity) and lifestyle changes (e.g., retirement) that occur with aging that make older
people more susceptible to positive energy balance and thus to weight gain.
An active lifestyle also is beneficial in preventing weight loss, an increasingly important
concern for the oldest sectors of the population (those older than 85 years) because of its
relation to metabolic disorders and functional ability. Several observational studies have
demonstrated the longitudinal benefits of even modest levels of physical activity on
preventing excess weight loss in older age, presumably through the maintenance and
preservation of lean mass (116-118).
Among intervention studies, training protocols are too variable and sample sizes are often
too small to establish dose-response relations between changes in weight and activity type,
duration, and intensity for different age subgroups. Nonetheless, some intervention studies
have demonstrated statistically significant improvements in various weight-related outcomes
(e.g., BMI, body fat distribution) with aerobic and resistance training in older participants
(e.g., 8;89;108), whereas others have not (104;105). The magnitude of improvement
observed in many of these intervention studies is similar, but is smaller than what is often
observed in younger populations given the same relative exercise dose. A similar relative
stimulus (say 75% of VO2peak) will translate into a lower absolute exercise dose in older
compared with younger people (due to lower levels of lean mass and aerobic capacity) and
therefore, may not result in an adequate stimulus for fat loss in older people. This may be
especially true for older women.
Question 5: How Do the Physical Activity Requirements for Weight
Maintenance Differ Across Racial/Ethnic and Socioeconomic
Groups?
Conclusions
Although some evidence suggests possible ethnic differences, the paucity of data,
particularly from the stronger longitudinal cohort or randomized, controlled intervention
study designs, makes it unwise to draw conclusions as to whether physical activity
requirements for weight stability or reduction differ by racial/ethnic or socioeconomic
groups.
Overview
Racial/ethnic disparities in obesity prevalence are robust and persistent across
socioeconomic groupings (e.g., 119-121). African Americans, American Indians/Alaska
Natives, Latinos and Pacific Islanders have substantially higher BMIs than do whites and
Asian Americans, and a significant interaction exists between ethnicity and sex (122). For
example, 54% of African American women are obese, compared with 42% of Mexican
American women and 30% of white women (4). This contrasts with the similar obesity rates
Physical Activity Guidelines Advisory Committee Report G4–15
Part G. Section 4: Energy Balance
among men: 34% of African Americans, 32% of Mexican Americans, and 31% of whites
(4).
Greater obesity implies a lesser ability to maintain weight and avoid weight gain, which may
be associated with less physical activity, more physical inactivity, or both. However,
racial/ethnic differences in the contribution of physical activity to weight maintenance have
been systematically examined only infrequently. Therefore, in addition to the reasons to
examine whether general physical activity recommendations should differ between
racial/ethnic groups (See Part G. Section 11: Understudied Populations, for a detailed
discussion of this topic), specifically exploring the possible need for different
recommendations to promote weight maintenance also is warranted. Available evidence
suggests at least 2 possible reasons for differential influences of physical activity on weight
maintenance by race/ethnicity:
1. Differences in the energy cost of physical activity, such that some ethnic groups
would appear to derive lesser benefits for weight maintenance at the same level of
physical activity (e.g., 123).
2. Differences in the relative contribution of physical activity and excess calories
(energy expenditure versus energy intake) to weight gain, such that some ethnic
groups would receive less benefit than others because physical activity contributes
less to the overall equation (124).
Experimental studies in exercise physiology have suggested that lower resting energy
expenditures and/or activity-related energy expenditures may contribute to higher rates of
obesity in Pima Indians and African Americans than in whites (123;125;126). However,
recent studies have demonstrated that these physiological differences may, in fact, be
explained by racial variations in body morphology (e.g., trunk versus limb length, organ
size) (127-129) that would not necessarily influence the ability to maintain weight. The
precise role in weight maintenance of racial/ethnic differences in resting or activity-related
energy metabolism (as opposed to age or sex-related differences) in body composition is an
important area for future research.
Rationale
The Energy Balance subcommittee used a search strategy to generate 236 articles from the
Physical Activity Guidelines for Americans Scientific Database (all age group combinations
except youth, with weight and BMI as the outcome of interest, excluding studies focused on
weight loss). These articles were further screened to identify studies that linked physical
activity to weight-related outcomes and met the following criteria: 1) targeting an ethnic
minority group; or 2) including subgroup analyses by ethnicity, not simply treating
race/ethnicity as a co-variate and adjusting for it; and 3) specifying the racial/ethnic
minority groups included in the analyses, not aggregating in the analyses as “non-white;”
and 4) having a sample size of 30 or more participants or at least 30 participants per study
arm; and 5) having a “general audience” sample (i.e., not focusing on a specific subgroup
Physical Activity Guidelines Advisory Committee Report G4–16
Part G. Section 4: Energy Balance
such as elite athletes or postpartum women). Even very recent studies in US locations that
have large ethnic minority populations, such as Baton Rouge, LA (130) and St. Louis, MO
(131), did not characterize their samples by race/ethnicity. A MEDLINE search using
similar parameters to those of the Scientific Database (key words: ethnic groups AND (body
composition OR body weight OR obesity) AND (physical activity OR exercise OR walking)
yielded 399 articles, most of which were already included in the Scientific Database. These
articles were then further screened by applying the above racial/ethnic minority
inclusiveness and sample size criteria, and eliminating those intervention studies in which
physical activity was not the dominant intervention component (i.e., nutrition was equally
strong or stronger). Reviews of relevant studies published after 1996 (132-135) and expert
referral produced an additional in press publication.
Of the 24 articles identified by this systematic review, half reported on studies that were
conducted outside the United States, including 9 in Asia/Pacific Islands (China, Japan,
Taiwan, India, New Zealand), 2 in Africa (Nigeria, South Africa), and 1 in Central America
(Mexico). Three were longitudinal cohort studies, 7 were interventions, and 14 were
cross-sectional studies.
Few of the 24 studies were population-based, and thus, findings may not be representative
even of subgroups with similar sociodemographic characteristics to those studied. Relatively
few studies included Latinos, currently the largest minority group in the United States, and
even fewer studies included American Indians, with their tremendous intra-ethnic
heterogeneity from diverse tribal origins and affiliations. Most studies of Asian Americans
or Pacific Islanders took place outside of the United States, introducing further complexity.
International studies were included, however, because so few domestic studies included
substantive racial/ethnic diversity, particularly among those with more rigorous designs.
These studies may assist in clarifying any influence of some biological or cultural
differences which may persist after migration to the United States, though they are likely to
be less applicable with regard to differences influenced by the specific environmental or
sociocultural context.
Of the 14 cross-sectional studies, which were conducted across a broad variety of
racial/ethnic minority groups, including African Americans, Nigerians, South Africans,
Pima Indians, Latinos, Asian Americans, Asians, and East Indians, most found an inverse
association between physical activity level and weight/waist circumference/body fat
percentage (29;103;113;136-146). This finding was consistent with studies in predominantly
white populations (147). Among elderly Chinese, tai chi or swimming were associated with
body fat distribution (lower levels in the thigh and/or abdomen), but not with total body
adiposity (145). The exceptions were found in: (1) a study of 7,503 Mexican-American
immigrants in Harris County, Texas, in which physical inactivity was correlated with
obesity in women but not in men (103); (2) a study of 44 African American women
(14% BMI less than 25, 25% to 30% Class II or III obese) in rural areas and small cities in
North Carolina, in which 3-day pedometer step counts were not correlated with BMI or
waist circumference (146); and (3) a study of 263 middle-aged Chinese in Hong Kong
Physical Activity Guidelines Advisory Committee Report G4–17
Part G. Section 4: Energy Balance
(40% obese, 30% completely sedentary), in which low levels of physical activity were not
correlated with BMI or waist circumference (144). In these instances, it is likely that BMI
and/or physical activity was insufficiently variable to detect an effect.
Longitudinal studies in predominantly white populations generally demonstrate associations
between increases in physical activity and decreases in the magnitude of weight gain (147).
Of the 3 longitudinal studies identified in ethnic minority populations, however, only one, a
4-city convenience sample across several US regions, The Study of Women’s Health Across
the Nation or SWAN, replicated this association (113). SWAN study outcomes revealed
associations between increases in daily routine physical activity (active transportation and
less TV viewing) and exercise/sports, and less weight gain. On the other hand, increases in
physical activity, compared to baseline, were not associated with smaller increases in
weight, as reflected in findings of no change or decreases in waist circumference (113). The
findings of the two nationally representative samples in the United States and Japan
(114;148) were essentially null. He and Baker (148) found that, between 1992 and 2000,
regular recreational physical activities, of any intensity, and work-related activities were not
associated with less weight gain. Race (Asian or white), education, and income were not
correlated with weight gain in multivariate analyses (148). However, although data were
adjusted for race/ethnicity, it is not clear whether differences in the physical activity-weight
gain association were analyzed by ethnicity. Lee and colleagues (114) found no baseline
association between physical activity and weight, though the mean BMIs were
23.5-23.7 across activity levels. This study apparently did not examine the relationship
between changes in physical activity and BMI changes. Thus, too few studies are available
to draw conclusions about the influence of race/ethnicity on the association between
physical activity and weight change over time.
Intervention studies selected for this review generally demonstrated that resistance training,
alone or in combination with moderate- to vigorous-intensity aerobic physical activity, was
necessary to produce changes in BMI or body composition/distribution in ethnic minority
populations (48;67;89;149-152), despite the effectiveness of aerobic physical activity alone
in improving non-weight-related aspects of the metabolic profile, such as reducing blood
pressure (67;149). Wilmore and colleagues (48) presented the only within-study
“head-to-head” inter-racial comparisons, with subgroup analyses after endurance training
using advancing intensity and duration on cycle ergometers. The magnitude of weight loss
for both whites and blacks was small; 0.2 kilogram (0.4 pound) mean weight loss in both
groups. The change was statistically significant in whites but not blacks likely due to the
larger sample size for whites (n=398) than blacks (n=159). Changes in various measures of
body fat followed a similar pattern, with small but somewhat greater changes occurring in
whites than blacks (e.g., change in sum of skinfolds for whites = −7.1±0.8, blacks =
−4.1±1.5, P<0.05 for both). The ages (34.8 and 32.3 years for whites and blacks,
respectively) and BMI (25.0 and 26.6 kg/m2, respectively) were similar. Adjustments for the
subtle racial/ethnic variations identified in experimental exercise physiology studies (e.g.,
128) apparently were not performed (48). Wilmore and colleagues (48) concluded that the
magnitude of the changes in body composition was not biologically significant in either
Physical Activity Guidelines Advisory Committee Report G4–18
Part G. Section 4: Energy Balance
blacks or whites and that a physical activity intervention of greater volume or longer
duration was needed to produce meaningful changes in body weight and fat. In another
study, in Japan, even quantities/intensities of walking sufficient to increase VO2max
(13,500 to 14,500 steps per day in the experimental groups versus 5,800 in the control
group) did not alter BMI, although the participants in this study were normal weight or
minimally overweight (24.6 to 24.7 and 25.2 kg/m2, respectively) (149). Participants were
presumably Japanese, although race/ethnicity of study samples is rarely specified in these
international studies. Contrasting findings were reported in another international study. In
this secondary analysis of data collected routinely on government health and social services
workers in Mexico, Lara and colleagues (152) demonstrated a 0.32 kg/m2 BMI decrease, a
1.0 kilogram (2.2 pound) weight loss, and a 1.6 centimeter (1.6 inch) decrease in waist
circumference at the end of 1 year after integrating mandatory 10-minute structured group
aerobic-calisthenic exercise breaks during paid work time in this group of mostly middleaged, overweight and abdominally obese workers. Although the study had no control group,
secular trends documented in Mexico at that time were similar to the United States mean
increases of 1 to 2 pounds (0.45 to 0.9 kilograms) in body weight and 0.5 inches
(1.27 centimeters) in waist circumference per year (113;152). The fact that the subjects of
the Mexican study were not volunteer participants, but rather a sample more typical of the
general population, and their overweight status, compared with the mostly normal weight
Japanese sample, may account for the discrepant findings.
As noted in earlier reviews (e.g., 132-134;153) there is an extreme paucity of evidence on
racial/ethnic minority groups with regard to the effects of physical activity on weight
maintenance. In this review, no 2 studies examined the same ethnic-sex samples — Japanese
middle-aged men, Japanese elderly adults, Japanese adults 30 to 69 years of age, Alaska
Native women, African American peri-menopausal women, African American and white
young and middle-aged adults, Mexican middle-aged adults — much less measures of
activity duration or intensity. Consequently, broad generalizations about the influence of
race/ethnicity on the physical activity requirements for weight stability or reduction are
premature.
Overall Summary and Conclusions
The overall conclusions of this chapter on physical activity and energy balance can be
summarized as follows:
Physical Activity, Weight Stability, and Weight Loss
Regular participation in physical activity provides benefits for weight stability, but with few
data on this topic from long-term studies, the optimal amount is not known. Available data
from short-term clinical trials indicate that a dose of physical activity in the range of 13 to
26 MET-hours per week results in a modest 1% to 3% weight loss, consistent with weight
stability over time (7-9). Thirteen MET-hours per week is equivalent to walking at a 4 mile
per hour pace for 150 minutes per week or jogging at a 6 mile per hour pace for 75 minutes
Physical Activity Guidelines Advisory Committee Report G4–19
Part G. Section 4: Energy Balance
per week. Aerobic physical activity done at this level would reduce upward migration of
individuals from one BMI category to the next. The wide range of physical activity levels
(13 to 26 MET-hours per week) needed for weight stability probably reflects individual
variation in the inherent (non-structured) level of physical activity and the degree to which
caloric intake is increased over time when a physical activity intervention is initiated. The
magnitude of weight loss resulting from resistance exercise in this review was typically less
than 1 kilogram (2.2 pounds). However, this may have been affected by the relatively short
duration of the study period and the increase in fat-free mass associated with this type of
intervention. Although a weight loss of 5% or more of body weight can be achieved with
large volumes of physical activity, a coincident dietary intervention is typically needed to
achieve this goal. The dietary intervention could include maintenance of (at pre-intervention
levels) or an actual reduction in caloric intake.
Physical Activity and Weight Regain
Most of the available literature indicates that “more is better” when it comes to the amount
of physical activity needed to prevent weight regain following weight loss. However, as
indicated above, the literature has some considerable shortcomings regarding the appropriate
research design needed to directly address this question. Studies by Ewbank and colleagues
(72), Jakicic and colleagues (73) and Schoeller and colleagues (74) indicate that the
volume of physical activity needed to prevent weight regain following weight loss is
approximately 31 MET-hours per week or 4.4 MET-hours per day. This is equivalent to
walking 54 minutes per day at 4 miles per hour or 80 minutes per day at 3 miles per hour, or
jogging for 26 minutes per day at 6 miles per hour.
Physical Activity and Body Composition Parameters
Ample evidence exists for a positive dose-response relation between the volume (frequency,
intensity, and duration) of endurance and/or resistance exercise, the training duration, and
the amount of total and regional fat loss. Moreover, the evidence suggests that regional fat
loss is greater with greater amounts of exercise-induced total weight loss and among those
with the greatest levels of adiposity. In the absence of coincident caloric restriction, aerobic
physical activity in the range of 13 to 26 MET-hours per week results in decreases in total
and abdominal adiposity that are consistent with improved metabolic function (7-9).
Thirteen MET-hours per week is equivalent to walking at a 4 mile per hour pace for
150 minutes per week or jogging at a 6 mile per hour pace for 75 minutes per week.
However, when more physical activity is done (e.g., 42 MET-hours per week), decreases in
intra-abdominal adipose tissue approach 3 to 4 times the level seen with this range of
physical activity (93).
Physical Activity Guidelines Advisory Committee Report G4–20
Part G. Section 4: Energy Balance
The Effect of Sex and Age on Physical Activity and Energy
Balance
Some evidence suggests that the amount of exercise necessary to maintain a constant body
weight differs between men and women and increases with age due to a variety of
physiological and lifestyle factors. Moreover, even within a given sex- or age-group, weight
loss responses to exercise vary substantially. Thus, it is quite difficult to make a standard
daily activity recommendation that relates to optimal weight maintenance for everyone. On
the other hand, the evidence base is too sparse at this time to recommend differential
physical activity prescriptions based on sex or on age alone.
Physical Activity Requirements Across Race/Ethnicity and
Socioeconomic Groups
Although some evidence suggests possible ethnic differences, the paucity of data,
particularly from longitudinal cohort or randomized, controlled intervention study designs,
makes it unwise to draw conclusions as to whether the effects of physical activity on weight
maintenance or loss differ by race/ethnicity or socioeconomic groups. Some of the questions
outlined in this section have yet to be fully addressed, although evidence is suggestive, for
example, that socioeconomic constraints, cultural preferences, and baseline levels of
sedentariness or obesity make low-intensity, social-environmental interventions feasible,
sustainable, and effective in many racial/ethnic minority groups (152;154-160). However,
simply conducting studies that include representative sample populations will not suffice,
because there likely will be too few members of any one group to disaggregate findings by
socioeconomic status, race/ethnicity, and sex, or to examine interactions between these
critical sociodemographic factors.
Research Needs
This review of physical activity and energy balance identified a number of research needs in
each of the topic areas covered in the chapter.
Physical Activity, Weight Stability, and Weight Loss
Studies that are appropriately designed, with sufficient statistical power, and of sufficient
length are needed to specifically examine the effects of varying doses of physical activity on
weight loss and weight stability across a variety of population groups, especially for those in
the normal BMI range. Further examination of effects of physical activity mode, intensity,
duration, and frequency on weight loss and/or weight stability also would make a valuable
contribution to this area. Finally, research is needed to further examine intervention
strategies that are most effective at promoting and maintaining sufficient doses of physical
activity that will facilitate weight loss and/or weight stability.
Physical Activity Guidelines Advisory Committee Report G4–21
Part G. Section 4: Energy Balance
Physical Activity and Weight Regain
Most available literature is observational or has relied on retrospective analysis of
self-selected and self-reported levels of physical activity. Use of state-of-the art technology
and complete energy balance designs are absent from the literature. Specifically, adequately
powered studies of sufficient duration with randomization to different levels of physical
activity after weight loss appear to be lacking. This limitation needs to be addressed to
adequately explore the question of how much physical activity is needed to prevent weight
regain following weight loss.
Physical Activity and Body Composition Parameters
There remains a need for more RCTs to distinguish exercise effects on total and regional fat
loss from those of weight loss per se. In addition, the large-scale use of imaging techniques
is necessary to distinguish the responsiveness of subcutaneous and visceral fat depots to
endurance and/or resistance training. The ability of studies to translate imaging findings into
simple anthropometric measures, such as waist or abdominal circumference, would increase
the clinical and personal utility of the research. Finally, there is a need to identify and to
study people who are very susceptible to weight gain in the current social environment and
who thus may be most resistant to weight or fat loss with exercise.
The Effect of Sex and Age on Physical Activity and Energy
Balance
Journal requirements stipulating that sex- and age-specific analyses be conducted with
sufficient statistical power would help to address the dearth of information pertaining to
individual and population differences in body weight response to physical activity. In
addition, it would be helpful to identify and study people in the current social environment
who are very susceptible to weight gain and who thus may be most resistant to weight or fat
loss with exercise. Studies of how susceptibility to weight gain or resistance to weight/fat
loss may vary by sex and age would contribute substantially to the obesity literature.
Physical Activity Requirements Across Race/Ethnicity and
Socioeconomic Groups
Two clear mandates emerge from this research synthesis. The first is to increase attention
and resources for studies that focus on diverse race/ethnicity groups and lower
socioeconomic status populations, or that include sufficient numbers to permit subgroup
analyses by race/ethnicity or socioeconomic status. The second is to establish standards for
peer-review journals that require investigators to report race/ethnicity of samples. These
standards also should require investigators to conduct subgroup analyses by race/ethnicity
and/or socioeconomic status if sample sizes are sufficient, rather than simply treating these
as co-variates and adjusting for them.
Physical Activity Guidelines Advisory Committee Report G4–22
Part G. Section 4: Energy Balance
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Physical Activity Guidelines Advisory Committee Report G4–37
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Part G. Section 5:
Musculoskeletal Health
Introduction
The Musculoskeletal Health Subcommittee reviewed the evidence for the role of physical
activity (PA) in bone, joint, and muscle health. With respect to bone health, the review
focused on osteoporosis because it is the most prevalent bone disease and because physical
activity is thought to play a role in the etiology of osteoporosis. In 2002, it was estimated
that 7.8 million women and 2.3 million men in the United States aged 50 years and older had
osteoporosis, and another 21.8 million women and 11.8 million men were at risk of the
disease because of low bone mass. By 2010, it is expected that the number of women and
men with osteoporosis will increase to 9.1 and 2.8 million, respectively, and the number of
women and men with low bone mass will increase to 26.0 and 14.4 million, respectively
(statistics from http://www.nof.org/advocacy/prevalence/index.htm; 21 January 2008).
Performing regular weight-bearing and muscle-strengthening exercises is one of the
universal recommendations for the general population to reduce the risk of falls and
fractures (1-3). However, more specific information on the type or volume of exercise that
should be performed is lacking.
With respect to joint health, the review focused primarily on osteoarthritis (OA), particularly
of the lower extremity, because of its high prevalence. It is estimated that 27 million women
and men in the U.S. aged 25 years and older have OA. The incidence rates are higher in
women than in men, particularly for knee OA (4). Physical activity and OA have a
potentially complex association, in that a certain level of mechanical joint stress is essential
for good joint health but excessive joint stress may promote the development of OA.
In contrast to bone and joint health, muscle health in not linked with a specific chronic
disease. Despite this, muscle mass and function are widely recognized as important
determinants of risk for such chronic diseases as osteoporosis and type 2 diabetes (5).
Muscle mass and function are also recognized as important determinants of physical fitness.
The review focused on physical activity as a mediator of both muscle quantity (i.e., muscle
mass) and quality (i.e., muscle function).
Physical Activity Guidelines Advisory Committee Report G5–1
Part G. Section 5: Musculoskeletal Health
Review of the Science
Overview of Questions Addressed
This chapter addresses 5 questions about the role of physical activity in bone, joint, and
muscle health:
1. Does physical activity reduce the incidence of osteoporotic fractures?
2. Does physical activity reduce risk of osteoporosis by increasing, or slowing the
decline in, bone mineral density or bone mineral content?
3. Does physical activity reduce or increase the incidence of osteoarthritis?
4. Is physical activity harmful or beneficial for adults with osteoarthritis or other
rheumatic conditions?
5. Does physical activity increase or preserve muscle mass throughout the lifespan?
Does physical activity improve skeletal muscle quality, defined as changes in
intrinsic and extrinsic measures of force-generating capacity, such as strength or
power?
For each question, the Musculoskeletal Health subcommittee considered whether such
factors as sex, age, or specific characteristics of the physical activity are important
determinants of the health-mediating effects. Effects of race and ethnicity could not be
examined because the majority of studies reviewed either did not include volunteers from
underrepresented minorities or did not conduct subgroup analyses by race/ethnicity.
Data Sources and Process Used to Answer Questions
Scientific articles related to physical activity and musculoskeletal outcomes were primarily
identified by using a systematic search process that relied on the Physical Activity
Guidelines for Americans Scientific Database (see Part F: Scientific Literature Search
Methodology for a detailed description of the Database). The systematic review and
subsequent article abstraction process was supplemented with previously published review
or meta-analytic papers, and key or important studies identified by the Musculoskeletal
Health subcommittee and consultants. Several systematic review or meta-analytic articles
and faculty-identified studies were used to document the scientific evidence pertaining to
physical activity and bone mineral density (BMD) and/or bone mineral content (BMC)
outcomes. The systematic review and abstraction process also was used to identify articles
related to physical activity and bone outcomes in men. Along with the systematic review and
abstraction process, review articles, and faculty-identified key studies were used to identify
papers and findings related to physical activity and joint outcomes, primarily focusing on
OA. Longitudinal cohort studies and case-control studies were located that evaluated some
Physical Activity Guidelines Advisory Committee Report G5–2
Part G. Section 5: Musculoskeletal Health
measure of physical activity as the exposure and incidence of OA as the outcome.
Randomized controlled trials (RCTs) were identified to determine the risks and benefits of
physical activity among persons with OA or other rheumatic conditions, such as rheumatoid
arthritis, fibromyalgia, lupus, and ankylosing spondylitis. Exercise interventions that were
primarily clinical (i.e., therapeutic physical or occupational therapy) were excluded. Review
articles and/or meta-analytic studies and a faculty-generated search for relevant studies were
used to evaluate the evidence for physical activity and muscle fitness.
Question 1. Does Physical Activity Reduce the Incidence of
Osteoporotic Fractures?
Conclusions
Physical activity is inversely associated with fracture risk (i.e., increased PA, decreased
fracture risk), particularly for fractures of the proximal femur. It also has a dose-response
relation with fracture risk, such that a greater volume of physical activity (i.e., frequency,
duration, and/or intensity) confers greater risk reduction. It is not currently possible to
identify more precisely the characteristics of the type or dose of physical activity likely to
optimize fracture prevention. Based on epidemiologic studies that evaluated dose-response
associations in various quantifiable manners, the minimal levels of physical activity that
were significantly associated with reduced fracture risk were at least 9 to 14.9 metabolic
equivalent (MET)-hours per week of physical activity, more than 4 hours per week of
walking, at least 1,290 kilocalories per week of physical activity, and more than 1 hour per
week of physical activity.
Rationale
No large RCTs have been conducted to determine whether the incidence of fractures is
decreased in response to physical activity. Therefore, definitive evidence for its efficacy in
fracture prevention is lacking. However, prospective cohort (6-16), retrospective cohort
(17), case-control (18-23), a small RCT (24), and cross-sectional (25;26) studies provide
moderate evidence for an inverse association of physical activity with fracture risk (i.e., high
levels of activity, low fracture risk). These studies also provide evidence for a dosedependent association with fracture risk, with higher levels of activity related to lower
fracture risk. Data that can be used to develop quantifiable recommendations for the type,
frequency, duration, and intensity of physical activity most likely to reduce fracture risk are
limited.
The likelihood that a RCT of PA with osteoporotic fracture as a primary outcome will ever
be conducted is remote because of the large sample size and long duration of intervention
that would be required. In this context, the consistency of findings, from both the population
studies considered in this section and the biomarker (i.e., BMD) studies considered for
Question 2, provides a solid evidence base for a role of physical activity in preserving bone
health. The optimal type and dose of activity necessary to maintain bone health is less clear.
Physical Activity Guidelines Advisory Committee Report G5–3
Part G. Section 5: Musculoskeletal Health
The evidence will be discussed with respect to whether the associations between physical
activity and fracture risk are consistent across the types of studies that have been conducted,
and whether findings are influenced by such factors as sex, fracture site, or type of activity.
Type of Study
Prospective cohort studies (6-16), a retrospective cohort study (17), case-control studies
(18-23), a small RCT (24), and cross-sectional (25;26) studies provide moderate evidence
for an inverse association of physical activity with fracture risk (i.e., high levels of activity,
low fracture risk). Overall, and without respect to the specific factors that will be considered
below (i.e., type of study, fracture site, sex specificity, dose-response association), all types
of observational and experimental approaches provided evidence for a role of physical
activity in preventing fractures. Of the 21 studies considered, only 3 reported no associations
(12;16;17), and 2 reported an association of physical activity with increased fracture risk
under some conditions (19;20).
Prospective and Retrospective Cohort Studies
Of the 12 prospective and retrospective cohort studies, 9 found beneficial associations of
physical activity with fracture risk (6-11;13-15); the others found no significant associations.
Of note, 2 of the latter studies focused only on vertebral fracture risk (12;16); and the third
focused on all osteoporotic fractures (i.e., hip, leg, wrist, pelvis, spine, rib, humerus,
clavicle, radius, and ulna) (17). Because the effects of mechanical loading on bone
metabolism are specific to the region undergoing loading, physical activity would not be
expected to have uniform effects in all skeletal regions. Also, the less consistent evidence
for an association of physical activity with vertebral fractures may be related to difficulties
associated with diagnosis.
Case-Control Studies
Most of the case-control studies were focused on hip fracture cases (18;20-23); only 1
evaluated the role of physical activity levels as a determinant of vertebral deformity (19).
Although all reported favorable odds ratios for a physical activity-related reduction in
fracture risk under some conditions, 2 studies noted a direct association (i.e., increased
fracture risk with increased activity) in certain cases (19;20). Silman and colleagues (19)
found that heavy levels of physical activity in early and middle adult life were associated
with increased risk for vertebral deformity in men (odds ratio [OR] 1.5 to 1.7; all P<0.01),
but not women. The same study found that current walking and/or cycling more than 30
minutes per day was associated with a reduced risk of vertebral deformity in women (OR
0.8; 95% confidence interval [CI] 0.7-1.0), but not men (OR 0.9; 95% CI 0.8-1.2). Stevens
and colleagues (20) found that vigorous activity was associated with a reduced risk for hip
fracture in older women and men who had no limitations in activities of daily living (ADLs)
(OR 0.6; 95% CI 0.4-0.8), but an increased risk (OR 3.2; 95% CI 1.1-9.8) in those who had
1 or more limitations in ADLs.
Physical Activity Guidelines Advisory Committee Report G5–4
Part G. Section 5: Musculoskeletal Health
Randomized Controlled Trials
One small RCT reported on the incidence of vertebral fractures (24). Women who had been
randomized to participate in a 2-year back strengthening exercise program or a non-exercise
control group were evaluated 8 years after the completion of the intervention trial. The
incidence of vertebral fractures was significantly lower in exercisers (1.6%) than in controls
(4.3%).
Cross-Sectional Comparison Studies
Nordstrom and colleagues (26) compared the incidence of fractures in former elite male
athletes (soccer and ice hockey players, aged 60 years and older) and age-matched male
controls. The incidence of fractures before the age of 35 years was higher in the athletes than
in controls (17.5% versus 12.9%, P<0.05), but athletes had fewer fractures than controls
after the age of 50 years (8.5% versus 12.9%, P<0.05). Ringsberg and colleagues (25)
evaluated fracture risk in older (aged 65 to 75 years) and elderly (aged 76 to 89 years)
women who reported regular participation in exercise classes (at least 1 hour per week) for
at least 20 years. They were compared with randomly selected age-matched women from
either urban or rural communities. The relative risk for any fracture was reduced in both
older (RR 0.50; 95% CI 0.33-0.79) and elderly (RR 0.28; 95% CI 0.13-0.56) regular
exercisers when compared with urban controls, but not when compared with rural controls
(older: RR 1.10; 95% CI 0.63-2.00; elderly: RR 0.63; 95% CI 0.24-1.43). Similar
associations were found when only fragility fractures were considered.
Summary
Cohort, case-control, and cross-sectional comparison studies all provide evidence for a
beneficial association of physical activity with fracture risk. A limitation of these types of
studies is that they do not isolate the role of physical activity as being causal in fracture
reduction. However, the general consistency of favorable findings across multiple studies
generates confidence that it plays a central role, if not a causal role, in the prevention of
fractures.
Type of Fracture
Hip Fractures
Findings show consistently favorable associations of physical activity with reduced hip
fracture risk (6-9;13;18;21-23;26). Many of these studies categorized participants by levels
of activity (e.g., tertile or quartile, hours per week) (6-9;13;18;21-23), and the relative risk
for hip fracture was significantly reduced in the most active group when the least active
group was used as the reference group (Figure G5.1).
Hip fracture risk was also increased in the least active group, when the most active group
was used as the reference group: Hazards Ratio=2.56 (95% CI 1.55-4.24) (13); reciprocals
of the hazards ratio and confidence intervals were calculated for inclusion in Figure G5.1. It
should be noted that prospective cohort studies query for physical activity level and then
monitor for fracture outcomes, whereas case-control studies query for physical activity after
identifying fracture cases and controls.
Physical Activity Guidelines Advisory Committee Report G5–5
Part G. Section 5: Musculoskeletal Health
Figure G5.1. Point Estimates of Relative Risk (± 95% Confidence Intervals) of
Hip Fracture From Studies That Examined Multiple Levels of
Physical Activity (Most Active Group Versus Least Active Group)
Relative Risk of Hip Fracture Most Active Versus Least Active
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
Boonyaratavej 2001
Farahmand 2000
Jaglal 1995
Kanis 1999
Feskanich 2002
Gregg 1998
Hoidrup 2001
Kujala 2000
Michaelsson 2007
prospective
cohort studies
case-control
studies
Note: Solid confidence intervals indicate studies of women; dashed confidence intervals indicate studies of men.
Michaelsson 2007 (13); Kujala 2000 (9); Hoidrup 2001 (8); Gregg 1998 (7); Feskanich 2002 (6); Kanis 1999 (23); Jaglal
1995 (22); Farahmand 2000 (18); Boonyaratavej 2001(21)
Figure G5.1. Data Points
Studies Sex Lower CI Point Estimate Upper CI
Prospective Cohort: Michaelsson 2007 (13) Men 0.24 0.39 0.65
Prospective Cohort: Kujala 2000 (9) Men 0.39 0.81 1.66
Prospective Cohort: Hoidrup 2001 (8) Men 0.55 0.76 1.07
Prospective Cohort: Hoidrup 2001 (8) Women 0.57 0.72 0.92
Prospective Cohort: Gregg 1998 (7) Women 0.45 0.64 0.89
Prospective Cohort: Feskanich 2002 (6) Women 0.32 0.45 0.63
Case-control: Kanis 1999 (23) Men 0.21 0.34 0.53
Case-control: Jaglal 1995 (22) Women 0.24 0.41 0.70
Case-control: Farahmand 2000 (18) Women 0.39 0.48 0.60
Case-control: Boonyaratavej 2001 (21) Women 0.18 0.35 0.69
Physical Activity Guidelines Advisory Committee Report G5–6
Part G. Section 5: Musculoskeletal Health
Vertebral Fractures or Deformity
Although both vertebral and hip fractures are of high clinical significance because of the
associated morbidity and mortality, the former are more difficult to diagnose because they
can occur without symptoms. Consensus also is lacking on what extent of vertebral
deformity constitutes a fracture. The few studies that have evaluated the association of
physical activity with risk of vertebral fracture (or deformity) have had discordant findings
(7;12;16;19;24). Heavy levels of activity in early and middle adult life were associated with
increased risk for vertebral deformity in men (ORs 1.5 to 1.7; all P<0.01), but not women
(19). In that study, current walking and/or cycling more than 30 minutes per day was
associated with a reduced risk of vertebral deformity in women (OR 0.8; 95% CI 0.7-1.0),
but not men (OR 0.9; 95% CI 0.8-1.2). Two other studies that assessed historical and recent
occupational and leisure-time physical activity found no associations with vertebral
fractures in women and men (12;16). However, in women aged 65 years or older,
participation in moderate- or vigorous-intensity sport or recreational activity was associated
with reduced risk for vertebral fracture (RR 0.67; 95% CI 0.49-0.94) when compared with
women who reported no participation in such activities (7). In a small prospective study of
women who had participated in an exercise program focused on strengthening back extensor
muscles, the prevalence of vertebral fractures 8 years later was significantly lower in the
exercisers than in the controls (1.6% vs. 4.3%; P=0.029) (24).
Wrist Fractures
Although the wrist is a common site of osteoporotic fracture, it is of lesser clinical
significance than the spine and hip because the associated morbidity and mortality is very
low. In the Study of Osteoporotic Fractures (7;26), physical activity was not associated with
risk of wrist fracture, whereas favorable associations with risk of hip and vertebral fractures
did exist. Physical activity was associated with reduced wrist fracture risk over 25.2 years of
follow-up in the Adventist Health Study (high versus none/low physical activity, relative
risk [RR] 0.61; 95% CI 0.41-0.87) (10), and former elite athletes were found to have a lower
prevalence of wrist fractures after the age of 50 years than were age-matched controls
(0.75% vs. 3.5%, P<0.05) (26).
All Fractures, Fragility Fractures, or Nonvertebral Fractures
Several studies have evaluated the association of physical activity with risk of any fracture
(11;13;20;25), fractures in weight-bearing versus non-weight-bearing regions (15), and
low-trauma, osteoporotic, or fragility fractures (14;17;25;26). The majority of these studies
found an association with reduced fracture risk (11;13-15;20;25;26), but there were
exceptions. Participation in vigorous levels of activity was associated with a reduced risk of
fractures in women and men with no limitations in ADLs, but an increased risk in elderly
with any ADL dependency (20). Joakimsen and colleagues (15) found that women and men
in the highest category of physical activity, compared with those in the lowest, had a
reduced risk for fractures in weight-bearing regions (RR 0.6; 95% CI 0.4-0.9) but not in
non-weight-bearing regions (RR 1.0; 95% CI 0.7-1.2). Among women and men in the
Physical Activity Guidelines Advisory Committee Report G5–7
Part G. Section 5: Musculoskeletal Health
Rancho Bernardo study, physical activity was not significantly associated with osteoporotic
fractures (17).
Summary
The evidence supports favorable associations of physical activity with reduced risk of
fractures. The evidence is most consistent for a reduction in hip fracture risk. Because the
proximal femur undergoes loading during walking and all activities that involve ambulation,
it is logical that an effect to reduce fracture risk would be most apparent at this site. The less
consistent findings for an association with reduced vertebral or other osteoporotic fractures
should not be interpreted as evidence that physical activity is not important for preventing
such fractures. It is likely that the instruments commonly used to assess total physical
activity do not adequately capture or characterize the potential site-specific skeletal benefits
of certain types of activity.
Sex Specificity
All of the studies that included women only reported favorable associations of physical
activity with reduction in fracture risk (Table G5.A1, which summarizes these studies, can
be accessed at http://www.health.gov/paguidelines/report/) (6;7;10;18;21;22;24;25).
Similarly, all of the studies that included men only reported favorable associations with
reduction in fracture risk (Table G5.A1) (9;13;14;23;26).
In contrast, the studies that included both sexes had discordant findings. Three of these
studies found no significant associations of physical activity with fracture risk when
analyses were performed by sex (12;16;17) or in women and men combined (17). However,
none of these studies was focused on hip fractures. Two studies reported an association with
reduced risk for any fracture in both women and men (11;20). Other studies found beneficial
associations of in women but not men (8;19), or in men but not women (15). Another noted
an adverse association in men, but not women (19).
Summary
Studies that included both women and men are characterized by greater discordance in the
results than those that included only women or only men. This causes a general concern
regarding the assessment of physical activity in studies that include both sexes. It is typically
categorized by participation in activities of varying intensity (e.g., mild = normal walking,
moderate = fast walking, strenuous = jogging (17)) and, in some cases, quantified by the
absolute intensity of the activity in metabolic equivalents (METs). However, these
approaches do not account for sex-related differences in the relative intensity. In
age-matched women and men, walking at a given speed or performing an activity of a
certain MET level represents a greater relative cardiovascular stress for women than men,
because women have a lower maximal aerobic power (27). Similarly, such activities may
also represent a greater skeletal stress in women, because bone size and mineral content are
less in women than in men. The failure to account for such sex-related differences in relative
intensity may result in miscategorization of level of activity. For example, fast walking may,
Physical Activity Guidelines Advisory Committee Report G5–8
Part G. Section 5: Musculoskeletal Health
indeed, be a moderate-intensity activity for older men, but is likely to be a strenuous activity
for older women. Although studies typically adjust for effects of sex (and age) in statistical
analyses, it is not clear whether such approaches adequately control for these issues. The use
of very broad categorizations (e.g., mild versus moderate versus strenous) may obscure true
associations of physical activity with fracture risk, and this would be expected to be of
greater concern in studies that included both women and men.
Physical Activity Dose-Response Pattern
Studies of laboratory animals indicate that the adaptation of bone to mechanical loading is
dose-dependent, with the intensity of the loading force being the key determinant of the
magnitude of the adaptive response (28). If these findings have relevance to human
physiology, it would be expected that associations of physical activity with fracture risk
would reflect a dose dependency.
Quantified Dose Response
Several studies evaluated physical activity in a manner that enabled the evaluation of a
quantifiable (in terms of frequency, duration, and/or intensity) dose-response association
with fracture risk. Some studies (6;7;18;23), but not others (8;9;12), found evidence of a
linear trend for increased volume of physical activity and reduced fracture risk. The manner
in which the dose was quantified varied among studies, including MET-hours per week,
kilocalories per week, and hours per week; none of these approaches facilitated the isolation
of intensity as a mediator of fracture risk. Among the studies that reported a significant
dose-response association, the minimal levels found to be significantly associated with
reduced fracture risk were: at least 9 to 14.9 MET-hours per week of physical activity (6),
4 or more hours per week of walking (6), 1,290 kilocalories or more per week of physical
activity (7), and 1 or more hours per week of physical activity (18;23). These levels were
associated with relative reductions in fracture risk of 33% to 41%. With increasing levels,
the relative reduction in fracture risk was 36% to 68%. Another study (6) found a doseresponse association of hours spent standing per day with reduction in fracture risk.
Standing 40 or more hours per week was associated with a 34% reduction in fracture risk.
One study (7) also found a significant dose-response association of physical inactivity,
quantified as hours per day spent sitting, and increased fracture risk. Sitting more than
8 hours a day was associated with a 37% increase in risk of fracture.
Categorical Dose Response
A few studies that used categorical methods (e.g., tertiles of activity, inactive versus active
versus very active) to evaluate dose-response associations of physical activity with fracture
risk found significant trends (6;7;10), whereas others did not (9;13;15-17;19;21;22).
However, even in the absence of significant linear trends, several of the latter studies found
that the highest categories of activity were associated with reduced fracture risk
(9;13;15;21;22); the relative reduction in risk ranged from 20% to 70%. Most of the methods
used to categorize level of physical activity were based on combinations of frequency,
duration, and/or intensity. Of the 3 studies that categorized physical activity by intensity
Physical Activity Guidelines Advisory Committee Report G5–9
Part G. Section 5: Musculoskeletal Health
(e.g., low versus moderate versus vigorous walking pace) (6;7;17), two found that
higher-intensity activity was associated with reduced fracture risk (6;7).
Change in Physical Activity
In the Nurses’ Health Study (6), the change in hours per week of leisure-time physical
activity was evaluated over the 6-year interval before the accrual of hip fracture data. A
non-significant trend (P=0.07) was apparent for women who were the least active (less than
1 hour per week) at the baseline assessment to have a decreased fracture risk if they reported
becoming more active. Conversely, a significant trend (P=0.004) was seen for the most
active women (4 or more hours per week) at the baseline assessment to have an increased
fracture risk if they reporting a decrease in activity level. Women who decreased their
activity level from 4 or more to less than 1 hour per week had more than a 2-fold increase in
hip fracture risk (RR 2.08; 95% CI 1.20-3.61). Among older women and men who were
performing heavy outdoor work, those who reported a decrease over a 2.5-year interval had
more than a 2.5-fold increase in fracture risk relative to those who maintained their level of
activity (RR 2.7; 95% CI 1.14-6.62) (11). A limitation of the study was that it could not rule
out the decline in physical activity as a consequence, rather than an antecedent, of the
fracture. Among women and men who participated in 3 Danish longitudinal population
studies (8), the change in physical activity over 2 assessment visits was evaluated as a
predictor of future fracture. Participants who had been moderately active and became
sedentary had a significant increase in relative fracture risk (RR 1.53; 95% CI 1.12-2.08).
However, those who moved from the sedentary to the most active group also had a
significant increase in fracture risk (RR 1.73; 95% CI 1.10-2.70). A case-control study
evaluated change in physical activity from the recalls of historic (ages 18 to 30 years) and
recent levels (18). This approach revealed no significant associations of either increases or
decreases in physical activity with fracture risk.
Summary
Studies that have used either quantitative or categorical methods of discriminating physical
activity dose generally support an inverse association between the level of activity and
fracture risk. However, such findings are not uniform across all studies. There may be
sex-and/or site-specific benefits that are not adequately captured in the instruments used to
assess physical activity. Limited evidence indicates that decreases in physical activity result
in increased fracture risk over only a few years in older adults. Evidence that increasing
physical activity leads to a reduction in fracture risk in older adults is lacking.
Corroborating Evidence
An advantage of studies conducted in laboratory animals is that the effects of mechanical
loading (i.e., physical activity) to enhance resistance to fracture (i.e., bone strength) can be
assessed in a direct and quantifiable manner. Such experiments have demonstrated that small
increases in BMD and BMC (e.g., 5% to 7%) translate into very large improvements in
resistance to fracture (e.g., 64% to 94%) (28). In contrast, the larger improvements in BMD
and BMC in response to bisphosphonate (e.g., 14% to 15%) (29) or parathyroid hormone
Physical Activity Guidelines Advisory Committee Report G5–10
Part G. Section 5: Musculoskeletal Health
therapy (e.g., 9% to 13%) (30) result in only proportional improvements in resistance to
fracture (e.g., 7% to 21% and 12% to 17%, respectively). If such findings in laboratory
animals are relevant to human physiology, it suggests that physical activity plays a critical
role in fracture prevention.
Consistency of Findings With Other Recommendations
Observational studies suggest that the minimal levels likely to reduce fracture risk are 9 or
more MET-hours per week of physical activity, 4 or more hours per week of walking, and
1,290 or more kilocalories per week of physical activity. These levels are consistent with the
current recommendations of the American College of Sports Medicine (ACSM) and the
American Heart Association (AHA) (3;31) and in the US Dietary Guidelines (32). However,
2 studies found that relative risk of fracture was significantly reduced with more than1 hour
per week of activity (18;23), suggesting that even lower amounts have benefit on bone
health. As reviewed in the ACSM Position Stand on Physical Activity and Bone Health (33),
fracture risk may be reduced both by the effects of physical activity on bone metabolism
(weight-bearing endurance and resistance activities), and by its effects to reduce the risk of
falling (resistance, balance, and flexibility activities). Currently, no evidence is available in
humans that the benefits of physical activity on fracture reduction can be achieved through
multiple short bouts versus a single longer daily bout. However, studies of animals suggests
that multiple short bouts should be more effective in enhancing bone strength than a single
bout (28).
Question 2. Does Physical Activity Reduce Risk of Osteoporosis
by Increasing, or Slowing the Decline in, Bone Mineral Density or
Bone Mineral Content?
Conclusions
Exercise training can increase, or minimize the decrease, in BMD in clinically relevant spine
and hip regions. The magnitude of the effect, when compared with changes in non-exercise
control groups, is approximately 1% to 2 % per year for studies up to 1 year in duration.
Studies involving longer periods of exercise training (i.e., more than 1 year) are sparse, but
suggest that the annual rate of BMD accrual does not persist. Importantly, studies of animals
indicate that small improvements in BMD in response to mechanical loading (i.e., exercise)
translate into very large increases in resistance to fracture. In contrast, increases in BMD in
response to pharmacological therapy (i.e., bisphosphonates, parathyroid hormone) translate
into proportional improvements in resistance to fracture.
Benefits on BMD have been found to occur in premenopausal women, postmenopausal
women, and adult men; the effects of physical activity on BMD of children are addressed
elsewhere in the report (See Part G. Section 9: Youth). Both weight-bearing endurance and
resistance types of exercise programs have been found to be effective in increasing BMD. A
key determinant of effectiveness is likely whether the exercise program appropriately targets
the skeletal region of interest.
Physical Activity Guidelines Advisory Committee Report G5–11
Part G. Section 5: Musculoskeletal Health
Rationale
Bone mineral density is the strongest predictor of fracture risk. Accordingly, many RCTs
and non-randomized clinical trials (CTs) have been conducted to evaluate changes in this
biomarker of fracture risk in response to exercise training, and even more cross-sectional
comparisons of BMD in sedentary versus physically active people and athletes in a variety
of sports and non-athletes have been published.
Because several meta-analyses of these studies have been conducted, the primary evidence
base used to address Question 2 was the meta-analytic findings (Table G5.A2, which
summarizes these studies, can be accessed at http://www.health.gov/paguidelines/report/). It
should be noted that 3 of the meta-analyses included individual subject data (34-36).
The evidence for an effect of exercise training on BMD will be summarized with respect to
whether findings are specific to skeletal region (lumbar spine [LS], femoral neck [FN], other
hip regions), population (i.e., premenopausal women, postmenopausal women, men), type of
exercise program (i.e., endurance or impact exercise, resistance or low-impact exercise),
type of study design (i.e., RCT, CT), and dose-response association.
Skeletal Region
Meta-analyses have most commonly assessed BMD of the LS and FN. Other sites include
the total hip, regions of the hip other than the femoral neck, the radius, and the os calcis.
Because it is fractures of the hip and spine that are of greatest clinical significance, the
discussion will focus on BMD of these regions. The methods of reporting the overall
treatment effect varied among studies, and included absolute (g/cm2) and relative (%)
change in BMD, annualized relative (% per year) change in BMD, and effect size. Results
will be discussed regarding whether changes in the reported parameters were statistically
significant and, when available, the general relative magnitude of the effect will be
provided.
Lumbar Spine Bone Mineral Density
Of the 15 meta-analyses, 13 evaluated whether an exercise intervention had a significant
effect on LS BMD (34;36-47) (Table G5.A2). Without regard to the population or type of
exercise studied, all but 3 of the meta-analyses found that exercise intervention resulted in a
significant benefit on LS BMD (36-41;43;45-47). The relative magnitude of the benefit was
generally 1 to 2% per year (i.e., difference between exercise and control groups). One metaanalysis reported a much larger benefit of exercise to increase LS BMD (10.7%) (45); this
will be discussed further in the population section (adult men) below.
Femoral Neck Bone Mineral Density
The second most commonly assessed skeletal region was the FN (34;35;37-40;42;47). Only
2 of these meta-analyses reported significant effects of exercise training (39;40). The
relative benefits of exercise on FN BMD ranged from 0.5% per year to 1.4% per year.
Physical Activity Guidelines Advisory Committee Report G5–12
Part G. Section 5: Musculoskeletal Health
Total Hip or Femur Bone Mineral Density
Regions of the proximal femur other than the femoral neck that have been studied were the
total hip or what was generically described as the femur (any subregion)
(38;41;42;45;46;48). Significant effects of exercise training on BMD were reported in
3 meta-analyses, with benefits of 0.4%, 2.4%, and 5.9% (45;46;48).
Summary
Meta-analytic studies generally agree that exercise training has beneficial effects on LS
BMD. Although a benefit of 1 to 2 % per year may seem small, this is roughly equivalent to
preventing the decrease in BMD that would typically occur over 1 to 4 years in
postmenopausal women and elderly men. Less evidence exists for beneficial effects of
exercise training on hip BMD. Because compliance to exercise training studies wanes as the
duration of the intervention increases, the majority of studies have been 12 or fewer months
in duration. The rates of increase in BMD observed in studies of less than 1 year in duration
do not appear to be sustained with longer-duration exercise training (49). Studies of
laboratory animals indicate that increases in bone mass continue only if the loading stimulus
is progressively increased, but it is unlikely that an exercise program with a continuously
increasing stimulus to bone could be carried out long-term in humans. However, in adult
men and women, an important goal of physical activity is to minimize age-related declines
in bone mass and strength. The extent to which decreases in BMD with aging can be
attenuated through long-term exercise training is not clear. Recent evidence indicates that
increases in BMD in response to a 1-year exercise training program can be maintained for
up to 4 years by regular exercise (49).
Populations
Premenopausal Adult Women
Several meta-analyses have either focused exclusively on premenopausal women or
conducted subgroup analyses of premenopausal women (34;37;39-41). Only one of these
studies reported no significant benefits of exercise training on BMD (34). That
meta-analysis was of individual subject data, and included only 3 published studies. The
other meta-analyses were generally consistent with the findings summarized above for
skeletal regions of interest.
Postmenopausal Women
Because the highest prevalence of osteoporosis is in postmenopausal women, it is not
surprising that the majority of meta-analyses have focused on this population, either
exclusively or in subgroup analyses (35;36;38-44;46-48). Only 3 of these meta-analyses
found no significant benefits of exercise training on BMD (35;42;44). Of these, one
excluded studies that involved any intervention other than exercise, including calcium
supplementation (42), one focused only on tai chi interventions (44), and one evaluated
individual subject data (35). The remaining meta-analyses involving postmenopausal
women were consistent with the findings summarized above for skeletal regions.
Physical Activity Guidelines Advisory Committee Report G5–13
Part G. Section 5: Musculoskeletal Health
Adult Men
Fewer RCTs and CTs of the effects of exercise training on BMD have been conducted in
men than in women. The only meta-analysis of studies of men included 2 RCTs and 6 CTs;
the studies evaluated BMD at any skeletal region (45). The overall effect size (ES) of 0.028
was not significant, but was equivalent to a difference in BMD of 2% between exercisers
(1.6%) and controls (-0.4%). Thus, the magnitude of the overall effect was similar to what
has been observed in women. Subgroup analysis for age revealed a significant ES (0.605)
for men older than aged 31 years (4.2% in exercisers versus -2.5% in controls), but not for
men aged 31 years or younger (ES 0.066). Subgroup analysis by skeletal region revealed
significant ESs for the LS (5.8% in exercisers vs. -4.9% in controls) and the femur (4.0% in
exercisers vs. -1.9% in controls).
Because only one meta-analysis of studies of men has been published, the Musculoskeletal
Health subcommittee also considered RCTs of the effects of exercise training on BMD in
men published after the meta-analysis (50-54). Only one of these studies reported significant
exercise-induced increases in BMD (51). In that study, 24 weeks of progressive
high-intensity resistance training resulted in greater gains in LS and whole-body BMD than
did moderate-intensity resistance training. The ineffectiveness of exercise training to
increase BMD in 3 of the other studies was likely because they were conducted at only low
to moderate exercise intensities (50;53;54) and because intensity was not progressively
increased (50;54). The study by McCartney and colleagues (52) involved a progressive
high-intensity resistance training program, but did not result in significant increases in
BMD. However, in that study, half of the 6 resistance exercises that were performed
involved relatively small muscle groups (i.e., ankle dorsi- and plantarflexion, arm curls) that
would not be expected to have a major influence on clinically important regions of the
skeleton. Thus, the volume of exercise performed that would be predicted to have favorable
skeletal effects was low.
Summary
Meta-analytic findings indicate that adult women and men can increase BMD at clinically
important skeletal regions through exercise training. Two analyses that included both
pre-and post-menopausal women found similar relative effects of exercise training on LS
and FN BMD in both populations (39;40). The other analysis that included both pre- and
postmenopausal women found similar relative effects of exercise training on LS BMD, but
effects on FN BMD in postmenopausal women only (41). Although some subgroup analyses
have suggested relatively greater effects of exercise on BMD in men than in women, this
must be interpreted cautiously. One of the RCTs was a study of the effectiveness of
resistance training (RT) to increase BMD in men following heart transplantation, and both
the decreases in BMD of controls and the increases in BMD of exercisers were of relatively
greater magnitude than is typically observed in healthy cohorts.
Physical Activity Guidelines Advisory Committee Report G5–14
Part G. Section 5: Musculoskeletal Health
Type of Exercise Program
Some of the meta-analyses evaluated effects of the type of exercise training, either by
restricting inclusion to certain types of exercise programs (34;37;38;41;43;44;47;48) or by
conducting subgroup analyses (40;46). The types of exercise programs have generally been
categorized as either endurance (i.e., aerobic) training (ET), with an emphasis on
weight-bearing activities, or RT (i.e., weight lifting). One meta-analysis focused specifically
on impact versus low-impact exercise training (40); the exercise programs were aligned with
the ET (i.e., impact) and RT (i.e., low-impact) categories referred to below. In general,
exercise programs can be categorized as to whether they introduce stress to the skeleton
primary through joint-reaction forces (i.e., low-impact, strengthening exercises) or
ground-reaction forces (i.e., impact).
Endurance Training
The meta-analyses that restricted inclusion to studies of ET have found beneficial effects
only on LS (43) and hip (48) BMD. One meta-analysis included only studies of walking and
found a significant effect on LS BMD, but not FN BMD (47).
Resistance Training
Four meta-analyses restricted inclusion to studies of RT (34;37;38;41). Three found a
significant effect of RT on LS BMD (37;38;41); the one that did not was a meta-analysis of
individual subject data (34). None of the analyses found significant effects of RT on BMD
of the FN (34;37;38) or other hip regions (41).
Endurance Training versus Resistance Training
Two meta-analyses included studies that involved either ET or RT exercise programs and
conducted subgroup analyses by exercise type (40;46). When considering any regional
BMD measurement (LS, radius, femur regions), Kelley found a significant overall effect of
RT (0.7%) but not ET (46). In contrast, Wallace and Cumming found significant effects of
both ET and RT on LS and FN BMD in postmenopausal women and on LS BMD in
premenopausal women (40). They found no effect of ET on FN BMD in premenopausal
women and the available data were not adequate to evaluate the effect of RT on FN BMD.
Summary
Evidence indicates that both ET and RT types of exercise programs can increase BMD at
both the LS and hip in adults, but this is not a consistent finding across all meta-analyses. In
particular, study findings differ as to whether RT has beneficial effects on BMD of hip
regions. This would be expected if RT programs did not include exercises that specifically
involved the musculature in the hip region, particularly because many of the exercises that
target other major muscle groups are commonly performed in the seated position (i.e., very
little load on the FN and other regions of the proximal femur).
Physical Activity Guidelines Advisory Committee Report G5–15
Part G. Section 5: Musculoskeletal Health
Type of Study Design
The majority of meta-analyses included studies in which the assignment to exercise and
non-exercise control groups was either randomized (RCTs) or non-randomized (CTs) (3537;39;41-45;47;48). Three included only RCTs (38;40;46) and 1 meta-analysis of individual
data was generated from only CTs (34).
Randomized Controlled Trials Only
All of the meta-analyses that restricted inclusion only to RCTs found beneficial effects of
exercise training on LS BMD (38;40;46); 2 also found significant effects on BMD of hip
regions (39;46).
Randomized Controlled Trials versus Non-Randomized Clinical Trials
Studies that evaluated whether outcomes differed by study design had discordant findings.
Wolff and colleagues (39) reported that increases in LS and FN BMD were 1.5- to 2-fold
greater in CTs (1.85 % per year, 1.39 % per year) than in RCTs (0.84 % per year, 0.89 % per
year). Kelley (48) found significant increases in hip BMD in CTs, but not RCTs, but in
another report (43), type of study design was not a significant determinant of the increase in
LS BMD. Although the meta-analysis of studies of men found that increases in BMD were
larger in RCTs, this finding appeared to be influenced strongly by the study of heart
transplant patients (see discussion above). Finally, Kelley and colleagues (41) reported that
study quality was a determinant of the increase in hip, but not LS, BMD, with higher quality
studies demonstrating a benefit. Randomization is one characteristic that contributes to high
quality, but other factors include blinding and attrition.
Summary
It is not clear whether non-random assignment to exercise and non-exercise groups results in
an over-inflation of the effects of exercise training on BMD. Importantly, meta-analyses that
restricted inclusion to RCTs reported favorable effects.
Dose–Response Pattern
The meta-analyses provided no evidence for dose-response effects of exercise training on
BMD. In some cases, when a study included two exercise groups that were distinguished by
exercise intensity, the meta-analyses included only the more intensive group (40;47).
Several of the meta-analyses by Kelley and colleagues evaluated characteristics of the
exercise programs (e.g., duration, intensity, compliance) using regression or correlation
analyses, but none of these yielded significant results (36;41;43;45;46;48). However, one of
the larger RCTs (n=140) of the effects of resistance exercise training on BMD of
postmenopausal women found a positive association between volume of weight lifted and
the change in BMD (55).
Physical Activity Guidelines Advisory Committee Report G5–16
Part G. Section 5: Musculoskeletal Health
Consistency of Findings With Other Recommendations
The findings from meta-analyses of the effects of exercise intervention on BMD and BMC
did not reveal dose-response effects. However, many of the intervention trials included in
the systematic reviews involved a volume of exercise that is consistent with the current
recommendations of the ACSM and the AHA (3;31) and in the US Dietary Guidelines (32).
The ACSM Position Stand on Physical Activity and Bone Health (33), which was based on
narrative review and consensus opinion, suggested that adults should participate in weightbearing endurance activities 3 to 5 days per week and resistance activities 2 to 3 days per
week at a moderate to high intensity (in terms of bone-loading forces) to increase, or prevent
excessive loss of, bone mass. The current review did not reveal any evidence to suggest that
the recommendation is inappropriate or should be modified.
Question 3. Does Physical Activity Reduce or Increase the
Incidence of Osteoarthritis?
Conclusions
In the absence of major joint injury, no evidence exists to indicate that regular moderate to
vigorous physical activity in amounts that are commonly recommended for general health
benefits increases the risk of developing OA. In addition, limited, weak evidence is available
from observational and animal studies to suggest that low-to-moderate levels of recreational
physical activity, particularly walking, may provide protection against the development of
hip and knee OA.
Introduction
Osteoarthritis is a relatively common degenerative condition of the hyaline cartilage lining
the joints and affects nearly 27 million US adults, manifested most commonly in the knee
and hip (4). Characterized clinically by joint pain, swelling, stiffness, and weakness, OA
often results in increased disability and significant negative personal effects on physical
function, mental health, and quality of life. Known major risk factors for OA include genetic
predisposition, older age, female sex, history of joint injury, occupational load, and excess
body mass (56-60). Historically, the “wear and tear” theory of joint degeneration suggests
that excess force on the joint cartilage, such as accumulates from vigorous sports and
occupational and daily living activities may initiate the pathophysiological process that
results in clinical OA (61). However, some level of physical activity is essential for joint
health. Thus, the physical activity guidelines for Americans should include a level of
movement or activity to ensure good joint health, while minimizing potential deleterious
forces.
The Musculoskeletal Health subcommittee examined the scientific evidence from
observational epidemiologic studies that have assessed some measure of physical activity
exposure before a determination of the OA status. In selecting studies from the Scientific
Database, the subcommittee used the following criteria, which were thought to be most
Physical Activity Guidelines Advisory Committee Report G5–17
Part G. Section 5: Musculoskeletal Health
helpful in informing the development of physical activity guidelines for Americans: 1)
included case-control or longitudinal cohort study design, 2) included participants typical of
the general community (not specialized subpopulations of elite athletes), and 3) assessed
and/or classified exposure in relation to the usual types and amounts recommended for
general health benefits (3;31). A total of 12 studies (8 longitudinal cohort, 4 case-control)
were used to address the research question.
Also examined were studies of elite, high-level athletes in specific sports activities to
qualitatively assess those activities that may be associated with an excess risk of incident
OA. Although not representative of the general population, studies of former elite and
professional level athletes provide insights that may be useful in informing physical activity
guideline development. Select sports have an increased risk of incident OA by virtue of such
factors as the inherent risk of joint injury, the extent of impact forces delivered to specific
joints, and/or the length of time and level of play while participating in the sport. We
identified 16 studies of elite athletic populations representing a variety of sports and
activities.
Rationale
Data from 12 observational epidemiologic studies suggest that no clear evidence exists that
regular participation in moderate- to vigorous-intensity PA, in amounts commonly
recommended for general health, infer a significant risk of incident lower-extremity OA
(Table G5.A3, which summarizes these studies, can be accessed at http://www.health.gov/
paguidelines/report/). Weak evidence indicates that walking and select other low-impact
activities may protect against the development of OA (Table G5.1).
Five of 8 cohort studies and 3 of 4 case-control studies reported at least 1 measure of
association below 1.0. For example, in a longitudinal study, participation in cross-country
skiing, walking, or swimming was associated with statistically significant protection against
OA (62). Theoretically, this is aligned with laboratory animal and human research showing
that exercise in moderate amounts results in beneficial changes to hyaline cartilage (greater
surface area, volume, glyccosaminoglycan content), synovial fluid nutrition and distribution,
and quality and strength of muscles surrounding the lower extremity joints, possibly without
increasing the presence of knee cartilage defects (63-66). These changes may improve the
shock absorption ability, thereby reducing forces transmitted to the joint cartilage.
Two longitudinal studies reported potential protective effects of walking on joint health. One
(67) reported odds ratios of 0.96 (95% CI 0.57-1.62) and 0.78 (CI 0.49-1.24) for incident
radiographic, symptomatic knee OA in adults who walked less than 6 versus more than 6
miles per week, respectively. In the other study (68), women who walked more than 5 miles
per week had significantly less joint space narrowing (OR 0.38, CI 0.15-0.93) than did
women who walked less than 5 miles per week (Table G5-1). A nested case-control
Physical Activity Guidelines Advisory Committee Report G5–18
Part G. Section 5: Musculoskeletal Health
Table G5.1. Studies Examining the Association Between Participation in Walking
and Risk of Hip/Knee Osteoarthritis
Study
(Year)
Study
Type OA Definition Walking Exposure
Measure of Association
OR (95% CI)
Hart et al.,
1999 (68)
Cohort Incident
radiographic:
1. Joint space
narrowing
2. Osteophyte
formation
Walking*
No = less than
5 miles per week
Yes = more than
5 miles per week
Joint Space Narrowing:
No = 1.0 (referent)
Yes = 0.38 (0.15 – 0.93)
Osteophyte Formation:
No = 1.0 (referent)
Yes = 0.60 (0.22 – 1.71)
McAlindon
et al., 1999
(69)
Cohort Radiographic
knee OA
Number of city blocks
walked per day
None = 1.0 (referent)
>4 = 1.2 (0.4 – 3.8)
Manninen
et al., 2001
(62)
Case
Control
Knee
arthroplasty
surgery
Regularly performed
exercise for at least
2 years?
Walking = Yes/No
Men:
No = 1.0 (referent)
Yes = 0.17 (0.02 – 1.46)
Women:
No = 1.0 (referent)
Yes = 0.32 (0.16 – 0.65)
Manninen
et al., 2002
(70)
Case
Control
Knee
arthroplasty
surgery
Occupational Walking:
Low
Medium
High
Low = 1.0 (referent)
Medium = 1.0 (0.65 – 1.53)
High = 1.06 (0.68 – 1.64)
Felson
et al., 2007
(67)
Cohort Radiographic,
symptomatic
knee OA
Do you walk for
exercise?
No <6 miles/week
>6 miles/week
No = 1.0 (referent)
<6 = 0.96 (0.57 – 1.62)
>6 = 0.78 (0.49 – 1.24)
CI, confidence interval; OA, osteoarthritis; OR, odds ratio
* No details were provided on the question used to determine walking in Hart el al (68). However, another published paper
from the same cohort described the walking variable as less than versus greater than 5 miles per week.
study (71) did not examine walking in isolation, but classified physical activity by the
amount of joint stress. Women who participated in activities requiring low joint stress,
which included walking, cycling and swimming, had a 42% (OR 0.58, CI 0.34-0.99) lower
risk of hip/knee OA than did women who were inactive.
However, some select groups of persons may have a moderately elevated risk of OA due to
long-term participation in high-impact activities (Table G5.2).
Physical Activity Guidelines Advisory Committee Report G5–19
Part G. Section 5: Musculoskeletal Health
Table G5.2. Select Individual Sports and Recreational Activities That Have Been
Associated With the Development of Osteoarthritis in at Least One
Study
Sports/Activities Associated
With Incident OA
Sports/Activities Not Associated
With Incident OA
Ballet/Modern Dance
Orienteering Running
Track and Field
Football (American)
Australian Rules Football
Team Sports
Basketball
Soccer
Ice hockey
Boxing
Weight Lifting
Wrestling
Tennis
Handball
Cross-Country Skiing
Running
Swimming
Biking
Team sports
Volleyball
Baseball
Walking
Gymnastics
Tennis (OA in hip/knee)
Rock Climbing
For example, competitive athletes who participate and train at high levels (e.g., elite,
professional sports, National Teams, Olympic athletes) in sports requiring high joint impact
(e.g., football, track and field, soccer) for many years have higher rates of incident knee or
hip OA than do non-athletes (Table G5.A3, which summarizes these studies, can be
accessed at http://www.health.gov/paguidelines/report/). Increased risk of OA has been
reported in one or more studies for the following sports: football (Australian rules), soccer,
track and field, basketball, boxing, ice hockey, orienteering running, wrestling, tennis, ballet,
and handball (see Part G. Section 10: Adverse Events for a discussion of muskuloskeletal
injuries related to these sports). The increased risk of OA in athletes in these sports may be
attributed, in part, to joint injuries, because these sports are also associated with the highest
rates of joint injuries (72;73), which is a strong risk factor for incident OA (57-59). In
addition, persons who have occupations that require excessive knee bending, kneeling, or
twisting/torsion movements or involve high-load weight bearing (lifting and carrying heavy
loads) and who also participate in moderate or vigorous recreational activity may have
increased risk for lower-extremity OA due to the additive effects over time (69;74).
Special Considerations
Sex
Women have a higher prevalence and incidence of most types of OA (57;75). Women also
have lower quadriceps muscle strength, one of the main muscles supporting the hip and knee
Physical Activity Guidelines Advisory Committee Report G5–20
Part G. Section 5: Musculoskeletal Health
(76;77), different anatomical and biomechanical structure (78;79), higher rates of obesity
(80), and participate in different types of physical activity than do men (81), and have
different risks of injury even in similar sports (72;73). All these factors can influence the
risk of OA related to physical activity, suggesting that the relationship may be sexdependent. For example, quadriceps muscle strength has been shown to be an independent
risk factor for the development of hip and knee OA even after controlling for excess body
weight, age, activity level, injury status, and physical fitness (76). In fact, the weak
protective effect of physical activity participation seems to be stronger among women than
men (62;68;70;71;82). Both Rogers and colleagues (71) and Manninen and colleagues (62)
reported that low and high levels of accumulated physical activity were protective for OA
among women (not all were statistically significant due to small sample sizes), but only high
levels were protective among men. A later study by Manninen and colleagues (70) also
reported a protective effect on severe knee OA among men and women combined. Because
that study was a matched (age and sex) case-control design, the independent effect of sex
could not be estimated.
Excess Body Mass
It has been demonstrated that overweight and obese individuals put more stress on their
lower-extremity joints during normal ambulation than do normal-weight individuals. This
suggests that overweight and obesity would exaggerate impact forces transmitted to the joint
during exercise and recreational physical activity, potentially increasing the risk of
developing OA. However, evidence suggests that elevated body mass index (BMI)
independently predicts incident OA, and that physical activity does not contribute
significantly to this increased risk (67). Physical activity plays an integral role in both
weight loss and the maintenance of normal body weight. Currently, no evidence supports the
possibility that promoting activity in the general US population, even among those who are
overweight or obese, will increase risk for OA.
Previous Injury
Previous joint injury is a well-established, independent risk factor for OA. In fact, athletes
who sustain major joint injuries, such as anterior cruciate ligament ruptures, and undergo
surgical reconstruction have premature onset OA (about 10 years early) compared with
non-injured athletes (83-86). Athletes in some sports that involve relatively high joint impact
(e.g., soccer) and who do not suffer a major joint injury do not seem to have excessive rates
of incident OA (87). However, in other sports (e.g., Australian Rules Football), both players
with and without previous knee injuries had an increased risk of radiographic knee OA (84).
Not all studies included in Table G5.A3 controlled for previous injury. (This table can be
accessed at http://www.health.gov/paguidelines/report/). Three studies that reported an
increased risk of OA associated with the highest level of physical activity (74;82;88) did not
control for previous joint injury, which may explain some of the excess risk. Sutton and
colleagues (89) reported an increased risk of knee OA with regular long walks (at least
2 miles at least 1 time per week), but this association was no longer significant after
Physical Activity Guidelines Advisory Committee Report G5–21
Part G. Section 5: Musculoskeletal Health
controlling for previous knee injury. McAlindon and colleagues (69) reported a significant
effect of more than 3 hours per day of heavy physical activity (combined occupational,
recreational, household and transportation domains) on symptomatic knee OA incidence,
even after controlling for previous joint injury, BMI, age, sex, and other potential
confounders. This finding is difficult to place into context in today’s society. Because of
changing job demands and increased technological advances in high-risk occupations (e.g.,
manufacturing, farming), it is likely that only a small fraction of the current US population
accumulates more than 3 hours of heavy physical activity per day.
Study Design Issues
It is interesting that the few studies that reported significant protective effects of physical
activity on OA incidence were case-control study designs (one was a nested case-control
within a longitudinal cohort). Case-control studies are strong and efficient study designs
when an outcome is rare. However, OA is a common condition when compared with the
incidence of some types of cancer or even diabetes. Therefore, some biases inherent to
case-control studies (e.g., recall bias, lack of representative controls) (90) may have
influenced the findings. This issue remains unclear, because 2 prospective cohort studies
(67;91) also reported measures of association that were below the referent level, although
not statistically significant, suggesting a possible protective effect for some groups.
Last, observational study designs such as these cannot determine cause and effect. However,
conducting an RCT to investigate the influence of different exercise participation on the
rates of incident OA is not feasible due to the long incubation period for OA development
and the potential ethical problems of randomizing persons to inactivity.
Some of the inconsistent findings also may be related to the methods used to collect and
analyze self-reported data. Historically, instruments used to query physical activity behavior
were designed to study the relation between activity and cardiovascular or mortality
outcomes. Hence, many instruments are geared more toward how physical activity may
affect the cardiorespiratory system versus the effects it may have on the musculoskeletal
system. As a result, the bone and joint loading effects of physical activity may be missed in
these studies. For example, jogging and swimming may be rated at the same MET level
based on their cardiovascular effects, yet these two activities are very different in terms of
loading delivered to the muscles, bones and joints. Hootman and colleagues (91) attempted
to address this issue in part by applying a “joint loading stress score” to the self-reported
data. However, the effects of joint loading physical activity on incident hip and knee OA
were still difficult to identify, even in this relatively large longitudinal study. Future research
should focus on teasing out the musculoskeletal effects from the cardiovascular effects in an
attempt to identify the types of activities involving high joint loading that may be associated
with increased risk of OA.
Another study design issue is the inconsistent definition of incident OA. Various outcomes
were used across studies including self-reported doctor-diagnosed OA, radiographicallydetermined OA (with and without symptoms), and incident hospitalization for joint
Physical Activity Guidelines Advisory Committee Report G5–22
Part G. Section 5: Musculoskeletal Health
replacement surgery. It is not known how these different definitions may affect the measures
of association.
Consistency of Findings With Other Recommendations
Our findings are not fully consistent with the results of a systematic review of sporting
activities on the development of hip OA (92) or the OASIS group (93), but do align with the
American Gerontological Society Consensus Guidelines for practice (94).
Lievense and colleagues (92) reported that moderate evidence exists that participation in a
combination of team sport and running activities is positively associated with the
development of hip OA. In addition, they reported conflicting evidence for ballet and soccer
participation and limited evidence for general athletics. This systematic review included
some of the studies reported in Table G5.A3, but also included studies published before
1995, the beginning point of this evidence synthesis (Table G5.A3 can be accessed at
http://www.health.gov/paguidelines/report/). Studies completed before the early 1990s may
have included subjects who were inherently different from more contemporary cohorts.
Also, Lievense and colleagues (92) noted that 4 of the older studies scored very low in terms
of study quality (less than 40 on a 100 point scale), which may have contributed to the
disparate findings.
The OASIS group (93) stated that considerable scientific evidence indicates that sport is a
risk factor for OA of the knee and hip, and that the risk correlates with frequency, duration,
and level of play. This is consistent with the evidence presented in Table G5.A3. However,
the OASIS group did not specifically address participation in general, moderate-intensity
physical activity. The OASIS summary recommendations also stated that joint injury and
excess body mass are much stronger risk factors for OA than sports participation. They
further recommended that the high-level athlete should be informed of the risk of OA
associated with sports and counseled regarding protecting joints from trauma and
maintaining optimal body weight. This guidance is an important risk communication
message for any person engaging in high-level sports activity over many years.
Summary
In the absence of joint injury, participation in recreational or leisure physical activities at
levels commonly recommended for general health benefits does not increase the risk of
developing OA. However, long-term high-level participation in select high-impact sports
(e.g., football, soccer, track and field) may be associated with increased risk of OA. As such,
health promotion messages should be developed to inform persons choosing to participate in
such activities that they may have increased risk for OA, and that modifying other OA risk
factors (e.g., maintaining normal body weight, preventing joint injuries) may help to lower
risk.
Physical Activity Guidelines Advisory Committee Report G5–23
Part G. Section 5: Musculoskeletal Health
Question 4. Is Physical Activity Harmful or Beneficial for Adults
With Osteoarthritis or Other Rheumatic Conditions?
Conclusions
Strong evidence indicates that both endurance and resistance types of exercise provides
considerable disease-specific benefits for persons with OA and other rheumatic conditions
without exacerbating symptoms or worsening disease progression. Adults with OA can
expect significant improvements in pain, physical function, quality of life and mental health
and delayed onset of disability by engaging in appropriate low-impact physical activity for
approximately 150 minutes per week (3 to 5 times per week for 30 to 60 minutes per
session). No evidence indicates that OA is a contraindication for participation in physical
activity among sedentary populations. However, patients should be counseled to pursue
activities that are low impact, not painful, and do not have a high risk of joint injury.
Introduction
More than 46 million adults in the United States have arthritis or another rheumatic
conditions and almost 40% of them are limited in their usual activities by their condition
(95). As a result of the aging of the population, the prevalence of arthritis is expected to
grow to 67 million by the year 2030 (96), and more than 44% of adults with arthritis are
sedentary (97). Because adults with arthritis make up a significant proportion (21%) of the
general US population (95) and have disease-specific barriers (e.g., pain, fatigue) to
initiating and maintaining physical activity (98-100), Federal authorities should consider this
patient population in the physical activity guideline development process.
To evaluate the evidence regarding the disease-specific benefits of PA among adults with
arthritis, the Musculoskeletal Health subcommittee examined RCTs published since 1995
(Table G5.A4, which summarizes these studies, can be accessed at http://www.health.gov/
paguidelines/report/). These studies met the following criteria: 1) included only patients with
arthritis or another rheumatic condition (e.g., OA, rheumatoid arthritis, fibromyalgia, lupus,
gout), 2) compared an exercise group (i.e., endurance and/or resistance exercise) with a nonexercise control group, 3) reported adequate information on the intervention (e.g., type,
frequency, duration), and 4) reported patient-oriented outcomes such as pain, physical
function, quality of life, and disability. Studies that described a clinically-delivered exercise
intervention (e.g., therapeutic physical or occupational therapy) were excluded.
Rationale
Table G5.A4 includes findings of 24 exercise intervention studies (15 endurance,
9 resistance, and 5 combined endurance plus resistance training) (Table G5.A4 can be
accessed at http://www.health.gov/paguidelines/report/). Interventions were included if the
exercise program described could feasibly be replicated in community settings (e.g., group
exercise classes, home programs) even if they were supervised by health care or research
Physical Activity Guidelines Advisory Committee Report G5–24
Part G. Section 5: Musculoskeletal Health
Physical Activity Guidelines Advisory Committee Report G5–25
professionals such as a nurse, physical therapist, or exercise physiologist. The 15 endurance
exercise studies represented 17 actual exercise versus non-exercise control comparisons,
because 2 studies (101;102) had multiple endurance exercise groups. Both endurance and
resistance exercise training programs demonstrated effectiveness for reduced pain, improved
function, and additional benefits on quality of life, mental health, self-efficacy (confidence),
and delayed onset of disability in ADLs.
Components of the Exercise Prescription
Table G5.3 summarizes characteristics of the exercise RCTs among those with arthritis or
other rheumatic conditions.
Many studies did not measure the actual dose of exercise delivered during the course of the
intervention, but prescribed doses of exercise across all 24 studies averaged 146 minutes per
week of moderate-intensity exercise, such as walking, cycling, tai chi, and water aerobics.
Average frequency (2.8 days per week) and duration of exercise sessions (51.8 minutes per
day) were consistent with current recommendations for people with arthritis (2003), and
with recommendations for the general adult population in the United States (3;31). The
length of the interventions varied considerably, ranging from 8 to 104 weeks.
Endurance Exercise Versus Control
The 15 endurance exercise studies (17 comparisons) included participants with OA (n=12),
fibromyalgia (n=4) and rheumatoid arthritis (n=1). The modes of exercise, all moderate
intensity, included walking (n=5), tai chi (n=5), water exercise (n=2), aerobics class (n=2),
and cycling (n=1). Participants exercised in small groups or at home for an average of 2.9
times per week and 48 minutes per session for a total average of 137 minutes per week.
Endurance interventions lasted an average of 23.9 weeks (range, 8 to 72 weeks). Sample
sizes were variable, with an average of 50 subjects in the exercise arm and 45 in the control
arm. Only 1 trial, the Fitness Arthritis and Seniors Trial (3 separate reports (103-105), had
more than 100 subjects in both the exercise and control arms.
Pain reduction and improvements in physical function were reported in the majority of
studies of endurance exercise. Other benefits included improved self-efficacy (confidence),
quality of life, muscle strength, mental/emotional health, and physical activity levels. No
increases in symptoms (pain, fatigue, stiffness) or other measures of disease activity
(e.g., global rating, radiographic progression, inflammatory markers) were demonstrated. In
fact, Schachter and colleagues (102) reported decreased disease severity (physician global
rating of severity and Fibromyalgia Impact Questionnaire total score) in response to exercise
training for subjects who adhered to both long-bout (one 30-minute bout per day) and
short-bout (two 15-minute bouts per day) programs.
Part G. Section 5: Musculoskeletal Health
Table G5.3. Summary Descriptive Characteristics of the Randomized Controlled Trials of Exercise Among Persons With
Arthritis or Other Rheumatic Conditions
Study Type
Number
of Studies
Average (Mean)
Characteristics
of Interventions
Number of
Intervention
Subjects
[Range]
Average (Mean)
Characteristics
of Interventions
Number of
Control Subjects
[Range]
Average (Mean)
Characteristics
of Interventions
Length (Weeks)
of Intervention
[Range]
Average (Mean)
Characteristics
of Interventions
Frequency
Per Week
[Range]
Average (Mean)
Characteristics
of Interventions
Duration (Min)
Per Session
[Range]
Average (Mean)
Characteristics
of Interventions
Total Prescribed
Dose (Min/Week)
[Range]
Significant Findings
(Number of
Studies/Outcome)
Endurance
versus Control
17† 50
[17–144]
45
[16–149]
23.9
[8–72]
2.9
[2–5]
47.8
[20–60]
137
[60–180]
10 ↓pain
8 ↑ function
1 ↑ quality of life
4 ↑ self-efficacy
4 ↑ muscle strength
2 ↑ physical activity
3 ↓ symptoms (other than pain)
4 ↑ mental/emotional health
5 ↑ or no change in symptoms/
disease activity
Resistance
versus Control
9 54
[10–146]
55
[10–149]
50.9
[8–96]
2.6
[2–3]
52.5
[30–60]
145
[60–180]
5 ↓ pain
5 ↑ function
6 ↑ muscle strength
3 ↓ stiffness
3 ↓ disease activity
4 ↓ disability
1 ↑ ROM
Combination
versus Control
5 62
[25–151]
64
[25–158]
44.0
[12–104]
3.0
[2–5]
55.0
[30–75]
156
[120–180]
1 ↓ pain
2 ↑ function
2 ↑ muscle strength
2 ↑ fitness/perceived exertion
2 ↑ no change in disease activity
1 ↑ mental health
1 ↓ body weight
All Studies 24‡ 54 52 39.6 2.8 51.8 146 –
* All studies implemented exercise interventions of at least moderate intensity.
†The endurance group had 15 individual studies, but 17 actual exercise versus control comparisons.
‡ Review included 24 individual studies, 2 studies compared multiple exercise groups versus a non-exercise control group and may be counted separately under the rows for the
endurance, resistance, and combination studies.
Physical Activity Guidelines Advisory Committee Report G5–26
Part G. Section 5: Musculoskeletal Health
Resistance Exercise Versus Control
The 9 resistance exercise studies included patients with OA (n= 5), rheumatoid arthritis
(n=3), and fibromyalgia (n=1) who exercised in groups at a clinic or other exercise facility
(n=7) or at home (n=2). Seven studies used isotonic (i.e., dynamic resistance exercise
involving concentric and eccentric actions) and 2 used isokinetic (i.e., variable resistance,
constant velocity) resistance training modes. Exercise occurred an average of 2.6 times per
week for 52.5 minutes per session, accumulating an average of 145 minutes per week. The
duration of resistance interventions ranged from 8 to 96 weeks (average 50.9 weeks). The
average number of subjects in the exercise arms was 54 versus 55 in the control arms. Only
one trial, the Fitness Arthritis and Seniors Trial (3 separate reports (103-105) had more than
100 subjects in both the intervention and control groups.
Benefits of resistance exercise for adults with arthritis included improvements in muscle
strength, symptoms (pain and stiffness), and function. Reduced risk of incident disability in
ADLs and improved measures of disease activity also were noted. Using two common
measures of disease activity (Disease Activity Score 28 [DAS28], which captures joint
tenderness, patient global rating of health, pain visual analog scale and erythrocyte
sedimentation rate, and the Larsen Score, which measures radiographic damage), 2 studies
of patients with RA reported significant improvements in DAS28 scores in response to
resistance training (106;107) and no worsening of the Larsen Score (106).
Combined Interventions Versus Control
The 5 studies that examined a combined endurance and resistance intervention included
patients with OA (n=4) and RA/inflammatory arthritis (n=2) patients. The mode of
endurance exercise was walking in 3 studies and cycling in 2 studies. The mode of
resistance exercise was either isotonic (n=3) or isokinetic (n=1). One study did not report
mode. Combined interventions occurred on average 3 days per week and averaged 55
minutes per session, for a total average weekly dose of 156 minutes per week. The average
duration of the combined interventions was 44 weeks (range 12 to 104 weeks). The average
number of subjects in the combined exercise arm was 62 versus 64 in the control arm.
Munneke and colleagues (108) and de Jong and colleagues (109) were the only studies that
had more than 100 subjects in each group.
Benefits of intervention programs that included both endurance and resistance exercise have
been similar to those reported for endurance-only and resistance-only interventions. The
benefits include reduced pain and improved function, muscle strength, fitness, and mental
health, with no increase in disease activity or symptoms. Weight loss and improved
satisfaction with function also were reported benefits. Specifically, the Arthritis, Diet, and
Activity Promotion Trial (ADAPT) (110) noted that the endurance plus resistance exercise
arm reduced body weight by 2.6% compared to 1.3% in the education control arm.
Physical Activity Guidelines Advisory Committee Report G5–27
Part G. Section 5: Musculoskeletal Health
Special Considerations
Appropriate Physical Activity Type and Dose
The exercise prescriptions in the reviewed studies varied widely on the frequency, duration,
intensity and type of physical activity. Thus, it is difficult to define either a minimum dose
of activity that results in clinical benefits for adults with arthritis or a maximum dose that
may be associated with increased symptoms or adverse events. The average minutes per
week of activity prescribed in these studies (146 minutes per week) suggests that a
prescription of 5 days per week for 30 minutes per session is likely appropriate for most
people with arthritis. All reviewed studies prescribed moderate to vigorous intensity and
low-impact activities. However, it is unclear whether some persons with arthritis can tolerate
higher-impact activities, such as team sports or tennis. It seems appropriate, given the
evidence, to guide persons with arthritis toward low-impact, moderate-intensity activities,
such as walking, cycling, water exercise, and tai chi.
In fact, walking may be a particularly relevant exercise mode for persons with arthritis,
especially in terms of disability prevention and safety. Walking was the exercise mode of
choice for 9 studies (6 endurance and 3 combined), and those studies reported benefits in
terms of reduced pain and improved function among persons with rheumatic conditions. No
true dose-response studies have been conducted, but evidence does suggest that higher
compliance to endurance and/or resistance exercise was associated with better outcomes,
including less disability and pain and improved physical function. Ettinger and colleagues
(103) used walking as the primary endurance component of the intervention and reported on
global ADL disability, an important patient-oriented outcome measure. The walking group
reported a significant 10% lower ADL disability score and the resistance training group an
8% lower score compared to the control group. A follow-up of this study cohort (105) found
that endurance exercise resulted in a 37% reduced risk of incident ADL disability and that
resistance exercise resulted in a 40% reduced risk. These studies are important to highlight
because of several critical design elements that are central to high study quality (111): 1)
large number of subjects (endurance = 144, resistance = 146, control = 149), 2) use of an
appropriate randomization protocol, 3) concealment of allocation to randomized groups, 4)
low loss-to-follow-up (83% completed study), 5) adequate adherence to the assigned
intervention (approximately 69%), and 6) use of an intent-to-treat analysis. In addition,
Ettinger and colleagues (103) reported adverse events related to the intervention, including 2
in the endurance exercise group, 3 in the resistance exercise group, and 1 in the control
group; only 2 of the 6 reported events resulted in injuries (1 in the endurance group, 1 in the
resistance group).
Important Outcome Measures
Pain
A recent expert consensus document from the international group, Osteoarthritis Research
International (OARSI), reported 25 evidence-based, patient-focused, recommendations for
the management of knee and hip OA. (112) One of the 11 non-pharmaceutical OARSI
recommendations states that all patients with hip and/or knee osteoarthritis should be
Physical Activity Guidelines Advisory Committee Report G5–28
Part G. Section 5: Musculoskeletal Health
counseled to engage in aerobic, resistance/strengthening, and range-of-motion exercises.
This recommendation was supported by the highest level of evidence rating (1a — based on
meta-analyses of RCTs) and had a ‘strength of recommendation’ rating of 96
(using a 0 - 100 visual analog scale). OARSI reported the effect of exercise on pain relief as
moderate, as pooled effect sizes reported were 0.52 (95% CI 0.34-0.70) for aerobic exercise
and 0.32 (95% CI 0.23-0.42) for resistance exercise.
Physical Activity Level
Even though the prescribed doses of physical activity in the studies included in Table G5.3
approached 150 minutes per week, a dose consistent with current recommendations, only 2
studies measured actual levels during the intervention (113;114). Both studies suggested that
the interventions did, indeed, increase actual activity levels. However, without monitoring
the actual participation, it is difficult to determine whether the intervention was ineffective
or whether a lack of effect was related to an insufficient increase in activity. Persons with
arthritis are known to have disease-specific barriers, particularly joint pain, to being
physically active (98-100). If an exercise intervention protocol does not adequately address
pain fluctuation during exercise, then persons with joint pain and stiffness may drop out at
high rates, have lower compliance to the prescribed dose, or not respond to the intervention
protocol as expected.
Quality of Life
Thirteen studies measured quality of life outcomes using various instruments, and 9 of those
reported benefits, mostly in terms of the function component of quality of life. Quality of
life, a concept that includes physical, mental, and emotional elements, is particularly
important for people with arthritis. Arthritis is not typically associated with excess mortality,
as are cardiovascular and other chronic diseases. However, it is associated with pain,
functional limitation, work disability, and loss of participation in valued life activities, which
severely affect quality of life. These results suggest that adequately measuring quality of life
as a primary outcome measure in arthritis interventions should be a priority.
Disability
Only 2 of 24 studies (103;105) included a measure of disability, as defined by the authors. In
terms of self-reported disability outcomes, the OARSI recommendations report pooled effect
sizes for self-reported disability of 0.46 (95% CI 0.25-0.67) for aerobic exercise and 0.32
(95% CI 0.23-0.41) for resistance exercise (112). The International Classification of
Functioning and Disability model purports participation restriction as an important concept
to capture in health studies. Participation restriction goes beyond limitation in specific
activities (e.g., climbing a flight of stairs, rising from a chair) by placing the activity
limitation in the context of a social role (115). For example, not being able to play the piano
(activity limitation) would be a significant disability (participation restriction) for a concert
pianist (social role), but not for someone who does not play the piano. Therefore, it is
equally important to include reliable and valid measures of function/activity limitation
(self-report or performance-based), as well as measures of participation restriction in studies
Physical Activity Guidelines Advisory Committee Report G5–29
Part G. Section 5: Musculoskeletal Health
of arthritis treatment interventions. Participation restriction was not an outcome measure in
any of the reviewed studies.
Adverse Events
Few studies reported adverse events, even though the CONSORT guidelines state it is
important to report even minor adverse events from RCTs (111). However, at least 14
studies reported that arthritis symptoms (pain and/or stiffness) were improved, or at least not
worsened, with exercise and at least 4 studies reported improvement or no increase in
disease activity. Of the 2 studies that did report intervention-related adverse events, Ettinger
and colleagues (103) reported that only 2 of 6 events resulted in injury, 1 each in the
endurance and resistance exercise groups, and Coleman and colleagues (116) reported no
major musculoskeletal adverse events. In addition, Fransen and colleagues (101) reported
that 4 participants dropped out of the study, 2 due to aggravation of knee pain (both in the tai
chi group) and 2 due to low back pain (1 each in the tai chi and hydrotherapy groups). These
reviewed studies, as well as others (117), noted that the frequency of study-related adverse
events were low among arthritis patients and older adults in general. This suggests that the
promotion of moderate physical activity, such as walking, cycling, and water exercise, is
likely safe in patients with arthritis. However, risk communication messages geared for this
population should include concepts such as “start low and go slow.”
Consistency of Findings with Other Recommendations
The above recommendations agree with the OARSI expert consensus guidelines (112), the
OASIS statement (93), the American Geriatrics Association Consensus Practice Statement
(94), and the MOVE Consensus (118). All 4 of these consensus documents recommended
that adults with OA participate in moderate-intensity, low-impact exercises with low risk of
injury. Both endurance and resistance exercises are recommended, accumulating
approximately 150 minutes per weeks, delivered either in group or home settings, 3 to 5
times per week for 30 to 60 minutes per session. The recommendations also are aligned with
disease management guidelines of the American College of Rheumatology and the European
League Against Rheumatism (EULAR) (119-121). At least 9 systematic reviews provide
additional support to the recommendations in the current report (122-130).
Summary
Current scientific evidence indicates that physical activity has important health benefits for
adults with arthritis, including reduced pain, improved function, and a reduced risk of
disability. Such benefits have been observed in adults with arthritis who participate in
moderate-intensity, low-impact activities (e.g., walking, cycling, water exercise), 3 to 5
times per week for 30 to 60 minutes per session (i.e., accumulate approximately 150 minutes
per week). Both endurance and resistance exercise, performed in group or home settings, has
been found to be effective.
Physical Activity Guidelines Advisory Committee Report G5–30
Part G. Section 5: Musculoskeletal Health
Question 5. Does Physical Activity Increase or Preserve Muscle
Mass Throughout the Lifespan? Does Physical Activity Improve
Skeletal Muscle Quality, Defined as Changes in Intrinsic and
Extrinsic Measures of Force-Generating Capacity, Such as
Strength or Power?
Conclusions
Specific modes and intensities of physical activity can preserve or increase skeletal muscle
mass, strength, power, and intrinsic neuromuscular activation. Such effects appears to be
similar in women and men and pervasive throughout the lifespan, although some evidence
indicates that the magnitude of the increases in skeletal muscle mass with resistance training
may be attenuated in advanced age. Specific types of activity can effectively increase
fat-free mass (i.e., lean mass), strength, and power. Specifically, performance of regular
(i.e., 2 to 4 times per week), high-intensity (i.e., 60% to 80% of the 1 repetition maximum
[1RM]), progressive resistance exercise can result in significant increases in muscle size,
strength, and neuromuscular function. Endurance activities have not been shown to increase
muscle mass or quality, but may be associated with an attenuation of loss. Muscle power
output may be a critical determinant of physical functioning in the elderly, and evidence is
emerging that resistance training performed at high velocity and low external resistance to
maximize muscle power output may have important beneficial effects on physical function
in older adults.
Introduction
Evidence indicates that the preservation of fat-free mass and, in particular, skeletal muscle
mass is associated with favorable health outcomes with advancing age. Cross-sectional
studies have reported that sarcopenia, the age-associated loss of muscle mass, is associated
with muscle weakness, functional limitations, and disability (131;132). Emerging evidence
for the effects of increasing adiposity on disability risk also have raised questions regarding
the relative importance of sarcopenia on age-associated disability (133-135). Despite these
observations, evidence remains for an important role of fat-free mass in maintaining
physical functioning and preventing disability with advancing age (131;136;137). Physical
activity and exercise interventions that have the potential to increase or preserve skeletal
muscle mass also may have important therapeutic benefits on improving physical
functioning and preventing disability, particularly in older adults (see Part G. Section 6:
Functional Health for a detailed discussion of this issue). Muscle mass also has been
reported to be a significant reserve of energy and a critical tissue for metabolic homeostasis
during stress and chronic disease. Thus, physical activity interventions designed to
increase or preserve muscle mass may be important for several health outcomes across the
lifespan (5).
Physical Activity Guidelines Advisory Committee Report G5–31
Part G. Section 5: Musculoskeletal Health
The effects of physical activity on muscle mass may mediate observed changes in muscle
strength and, as such, are important to men and women of all ages. For example, exerciseinduced increases in muscle strength are associated with improved muscular fitness in
formerly sedentary obese individuals (138;139). This is particularly noteworthy because
sedentary overweight and obese individuals have a limited exercise capacity (140), which
may impair physical function. In older individuals, the age-related loss of muscle mass is
accompanied by losses in voluntary muscle strength (141). Consequently, in those at risk of
sarcopenia, functional capacity and mobility are likely to be comprised. Studies conducted
in older adults indicate that increases in lower body strength are associated with
improvements in gait parameters (142;143), functional capacity (144-147), and bone health
(51;148;149). Strength adaptations also have been suggested to mediate increased endurance
(150).
Given the current scope of physical inactivity in the United States and the declines in muscle
quality parameters that begin in early adulthood, interventions designed to prevent declines
in muscle quantity and quality through physical activity should be focused on all ages of the
population. However, because the percentage of older Americans is increasing rapidly and
the associated detriments in function may similarly escalate, a special emphasis on the
importance of musculoskeletal health should be placed in this population to prevent the
substantial economic costs associated with decreased physical functioning that result from
the loss of muscle mass and muscle weakness.
Rationale
Physical Activity and Muscle Mass
Many studies have examined the role of physical activity on changes in body composition.
Because of the association between muscle strength, power, and muscle mass and the well
described age-related declines in skeletal muscle mass, we examined the literature on the
influence of exercise training interventions, in particular resistance training interventions, on
changes in muscle and fat-free mass. Studies that were evaluated included trials conducted
in young, middle-aged, and older men and women. Very few studies, if any, examined
subgroups of different ethnic populations to evaluate variations in responsiveness.
The effects of progressive resistance training in young healthy men and women have been
well described (151). As reviewed by Kraemer and colleagues, high-intensity progressive
resistance training in young adults results in significant increases in dynamic strength,
explosive power, and muscle mass. More recent studies have confirmed these findings.
Short-term studies of both lower- and upper-extremity resistance training have demonstrated
increases in muscle cross-sectional area (CSA) in men (152-154) and women (155), with
corresponding increases in muscle strength.
Sex-specific changes in muscle mass or CSA in response to resistance exercise training have
been investigated. Short-term studies of progressive resistance training noted similar
increases in muscle adaptations of men and women (156). Increases in muscle CSA by
Physical Activity Guidelines Advisory Committee Report G5–32
Part G. Section 5: Musculoskeletal Health
computed tomography (CT) have also been shown to be similar in men (17.5%) and women
(20.4%) in response to 16 week of upper- and lower-extremity high-intensity resistance
training (157). However, one study employing elastic bands for resistance training noted
significant increases in muscle fiber CSAs in men, but not women, in response to 8 week of
training, with 2 - 3 sessions per week (158). Interestingly, one RCT of adolescent girls
demonstrated that a 5 day per week mixed mode endurance training program (running,
aerobic dance, competitive sports) induced a significant (4%) increase in mid-thigh muscle
volume (159). More recently, assessment of fat-free mass by dual-energy x-ray
absorptiometry (DXA) and serial CT scans to measure muscle volume confirmed that
similar increases in muscle mass and volume occurred in young men and women in response
to a 6-month whole-body program of progressive resistance exercise training (160). These
results suggest that resistance exercise training can increase muscle strength and mass to
similar relative extent in men and women. Other modes of physical activity may increase
fat-free mass during adolescence.
Several studies have assessed combinations of the number of repetitions and intensity of
resistance training required to maximize gains in muscle strength and mass in young adults.
Campos and colleagues compared the responses to 8 weeks of 3 different regimens of
progressive resistance training (161). Young healthy men were randomized to perform
low-repetition/high-intensity, intermediate-repetition/moderate-intensity, or high-repetition/
low-intensity progressive resistance training of the lower extremities (leg press, squat, and
knee extension). Increases in muscle fiber hypertrophy and muscle strength were greater in
the low-repetition/high-intensity and intermediate-repetition/moderate-intensity groups than
in the high-repetition/low-intensity group. In contrast, Hisaeda and colleagues observed
similar gains in peak torque and muscle CSA in young women in response to 8 weeks of
either high-intensity/low-repetition or high-repetition/low-intensity resistance training (155).
The influence of the number of sets performed at each training session on changes in muscle
strength and mass in response to resistance training also has been studied. Ronnestad and
colleagues demonstrated that 3 sets of lower-body resistance exercise per session was more
effective than 1 set in increasing muscle strength and CSA, suggesting that the volume of
training may drive the gains in muscle strength and mass (162). In support of this, varying
the number of training days per week and the number of training sets performed to control
the total volume of work performed per week resulted in similar gains in muscle strength
and CSA in young men and women (163). The evidence from these trials suggests that
muscle hypertrophy from resistance training occurs in a dose-dependent manner that is
primarily dependent on the intensity of the resistance.
As reviewed by Fielding, a number of early studies demonstrated the positive effects of
progressive resistance training on muscle mass in healthy older men and women (164).
More recent short duration randomized trials have confirmed these initial findings (165168), and one study has demonstrated that muscle mass can continue to increase in older
adults throughout 2 years of resistance training (52).
Physical Activity Guidelines Advisory Committee Report G5–33
Part G. Section 5: Musculoskeletal Health
The influence of age, per se, on changes in muscle mass in response to training also has been
investigated. Although resistance exercise training interventions can increase both whole
muscle and fiber CSA in older men and women, some evidence indicates that this
hypertrophic response is attenuated in old age. Cross-sectional studies of older bodybuilders
who had been performing resistance training for 12 to 17 years were reported to have midthigh muscle CSAs that were similar to young sedentary controls, suggesting that the ability
to stimulate muscle growth is diminished with age (169). In young men and women, the
change in mid-thigh CSA after 4 months of high-intensity resistance training is typically
16% to 23 % (157), compared to a 2.5% to 9.0% increase in institutionalized or frail older
individuals in response to similar resistance interventions (170-172).
Few studies have directly compared increases in muscle hypertrophy in young and older
subjects using a similar standardized training intervention; comparisons across studies are
prohibitive due to differences in subject selection criteria, the specific training intervention
employed, and the techniques implemented to assess muscle mass. Welle and colleagues
reported impaired responses of both knee and elbow flexors, but not knee extensors, after a
whole-body resistance training program in older compared to young men and women (173).
Hakkinen and colleagues reported a decline in the adaptive response of the vastus lateralis
from middle to old age of approximately 40% (174). Lemmer and colleagues reported a
significant increase in thigh muscle CSA in both young and older adults following resistance
training; the magnitude of the increase was greater in the young (175). Similar results also
were observed by Dionne and colleagues following 6 months of resistance training in young
and older non-obese women (176). In contrast, resistance training studies of similar intensity
and duration also have been reported to generate similar changes in thigh CSA in young and
old (160;177). These findings suggest that progressive resistance training-induced increases
in muscle mass can occur in older individuals, but that the magnitude of the response may be
attenuated, particularly in the oldest old.
Whether the anabolic response to resistance training among older adults is sex-specific
remains equivocal. Several studies have reported similar increases in muscle mass in older
men and women in response to resistance training (52;160;178;179). In contrast, men were
found to have larger increases than women in muscle volume after 9 weeks of high-intensity
resistance training (177) and larger increases in fat-free mass after 12 weeks of highintensity resistance training (180). At the cellular level, Bamman and colleagues found a
greater degree of hypertrophy of both type I and II fibers in older men than in older women
in response to 26 weeks of high-intensity resistance training (181). However, in contrast to
these reports, Hakkinen and colleagues found a smaller increase in muscle CSA in older
men than in older women (174). Despite some lack of agreement, the majority of studies
evaluated suggested that sex plays a relatively small role in the magnitude of the
hypertrophic response to resistance exercise training in older adults.
Physical Activity and Strength
Several studies have documented gains in strength as a direct result of resistance training
regimens throughout the lifespan (182;183). In young men, a 2-week isokinetic resistance
Physical Activity Guidelines Advisory Committee Report G5–34
Part G. Section 5: Musculoskeletal Health
training program increased isokinetic and isometric quadriceps muscle peak torque at both
60 and 240 degrees (184). In another study of men, a 12-week high-intensity resistance
training program resulted in an increase in isokinetic concentric (quadriceps) knee extension
strength at a velocity of 30 degrees and eccentric (hamstring) knee joint strength at
velocities of 30, 120 and 240 degrees (185). The hamstring/quadriceps ratio also increased.
A dynamic resistance training protocol of similar duration resulted in isometric torso
rotation strength gains in men and women who exercised twice weekly for 12 weeks (186).
Significant gains in both upper- and lower-body strength have also been reported for longer
studies (6 months) (138). Although the preferential mode for strength gains has been
dynamic resistance training (139;187;188), with inclusion of some amount of eccentric
contractions (189), some studies indicate that other modes also may be effective, including
nordic training (190), circuit weight training (153), balance training (191), and a
combination of strength and endurance or endurance-only protocols (188;192).
In middle-aged men and women subjected to short-duration physical activity interventions,
strength gains also have been observed after progressive resistance (150), endurance (193),
and multi-modal aerobic/weight (194) training protocols. Gains in strength are evident in
longer duration studies (4 to 6 months) in this age group (195;196), and further demonstrate
that greater gains in strength begin to occur after 8 weeks of a combined resistance and
endurance exercise protocol (196).
In older adults, investigators have used relatively long duration (4 to 12 months) resistance
training alone (142;143;145) or in combination with endurance training (144;146;197-199),
endurance/balance (200), or endurance/strength/balance/coordination/flexibility (201)
regimens to successfully increase strength in an effort to counteract the late-life decline in
physical functioning. Although resistance training induces muscle strength gains, functionaltask exercises may be more effective at counteracting declines in function (202). It has been
suggested that gains in isometric and dynamic muscle strength (199) and in isokinetic
muscle strength (145) are associated with improved physical functioning. However, the
gains in strength may be muscle-specific and translate into improvements only in select
parameters of physical functioning, as indicated in both long- (146;203;204) and shortduration exercise interventions (205). The results of these studies are in agreement with a
large systematic review (206) of 62 RCTs of resistance training in older men and women
(older than age 60 years), which found that resistance training increased muscle strength and
had a modest significant effect on some measures of physical functioning (e.g., gait speed).
Strength gains also have been reported for shorter (8 to 12 week) duration studies of older
adults. These studies have employed dynamic training (179;207), exclusively eccentric
resistance training (147), an integration of resistance, endurance and balance types of
activities (208-210), or endurance-only activities (211). A progressive resistance training
protocol in older adults resulted in a linear increase in dynamic strength at different time
points of a 12-week study (212). Other intervention paradigms for functional improvements
have been explored. In an 8-week comparison between a combined resistance
training/functional training regimen (1 day per week of each) and resistance training only
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Part G. Section 5: Musculoskeletal Health
(2 days per week), both programs resulted in significant gains in dynamic strength (213).
However, others report a dose-response relationship between high-intensity progressive
resistance training and functional capacity that may explain the preponderant use of this type
of resistance training (145;214). Gains in strength also occur with low- (215) and variableintensity resistance training (6 months) (216;217).
Physical Activity and Muscle Power
Although physical activity interventions that increase or maintain muscle strength have
important health implications, emerging evidence suggests that muscle power (the rate at
which muscle force can be generated) may play a more important role in functional
independence and fall prevention, particularly among older adults. Muscle power has been
shown to decline more precipitously with aging than does dynamic and isometric strength
(218). Lower extremity muscle power also is a strong predictor of physical performance,
functional mobility, and risk of falling among older adults (219;220). Muscle power has
been found to be inversely associated with self-reported disability status in communitydwelling older adults with mobility limitations (221;222) and is a better discriminator of
mobility limitations than muscle strength (220).
Most trials that have evaluated the effects of progressive resistance training on muscle
strength and mass have traditionally involved relatively slow movement velocities. Some of
these have examined changes in lower extremity power output. In a study of nursing home
residents, progressive resistance training resulted in an increase in muscle strength of more
than 100%, but only a 28% increase in stair climbing power, suggesting a disproportionate
and specific rise in strength versus power with traditional resistance training (171). Skelton
and colleagues also examined changes in peak leg extensor power in response to 12 weeks
of traditional resistance training in older women (223). They observed increases in strength
of 22% to 27% with a non-significant increase in leg extensor power. A randomized trial by
Joszi and colleagues also noted a modest improvement (30%) in leg extensor power in
response to 12 weeks of progressive resistance training in healthy older men and women
(224). More recently, Delmonico and colleagues examined the effects of moderate-velocity
resistance training on changes in peak power in older men and women (225). They observed
similar changes in absolute peak power in response to 10 weeks of resistance training in
both older men and women. However, the relative improvements in peak power were greater
in women (16%) compared to the men (11%). Similar results have also been reported by
Newton and colleagues employing a “periodized” resistance training intervention in healthy
young and older men (226). These studies suggest that traditional slow velocity resistance
training results in minimal improvements in peak power, that adaptations may be sexdependent, and that resistance training performed at relatively slow velocities may lack the
specificity to improve peak power, particularly in older individuals.
Early randomized trials that examined high-velocity resistance training to increase muscle
power in older subjects compared the effects against walking exercise (227), slow velocity
resistance training (228), or slow velocity isokinetic training, (229). In general, these studies
all demonstrated that interventions designed to maximize muscle power are feasible, well
Physical Activity Guidelines Advisory Committee Report G5–36
Part G. Section 5: Musculoskeletal Health
tolerated, and can dramatically improve lower-extremity muscle power in healthy older men
and women and older women with self-reported disability. Earles and colleagues reported a
50% to 141% increase in leg power in older women and men following 12 weeks of highvelocity resistance training in combination with moderate-intensity non-resistance exercise
compared to a structured walking program (227). Fielding and colleagues compared highvelocity lower-extremity resistance training with traditional slow-velocity resistance training
in older women with self-reported disability (228). They observed an 84% greater increase
in leg press power in the high-velocity training group. Similar results were reported by
Signorile and colleagues in healthy older men and women in response to 12 weeks of
high-velocity isokinetic training (229). All of these studies employed high-velocity training
at a relatively high external resistance. Only one study to date has examined high-velocity
training at varying levels of external resistance (measured as a percent of the 1 RM) (230).
Older adults were randomized to 12 weeks of high-velocity resistance training at 20%, 50%,
or 80% of 1 RM. Peak power output improved similarly across all training intensities,
suggesting that speed of movement is a key factor in generating improvements in power
output.
A small number of studies have evaluated different types of exercise interventions that did
not depend on specific resistance training equipment or isokinetic dynamometry, but
emphasized explosive power. These have included modified calisthenics and plyometric
(i.e., jumping) exercises (231), stair climbing (232), and weighted-vest exercise (233). Bean
and colleagues compared 12 weeks of a weighted stair climbing program (i.e., stair climbing
while wearing a weighted vest) to a walking program in older adults with baseline mobility
limitations (232). When compared with walking, the stair climbing intervention increased
leg power by 17% with a corresponding 12% increase in stair climbing power. The same
group also examined the effects of a program of weighted vest exercise performed at a high
velocity (InVEST) compared to a slow-velocity training program (233). Lower-extremity
power and chair rise time were increased more in the InVEST group. Surakka and
colleagues examined the effects of a group exercise intervention that consisted of leg and
trunk exercise that emphasized both strength and power training (231). They observed that
the explosive power training intervention resulted in improved perceived fitness compared
to non-exercising controls. These studies confirm that several types of exercise programs
that can be performed at high velocity can improve muscle power and improve physical
functioning.
A few studies have evaluated the influence of power training on changes in physical
functioning in older adults (234-237). Sayers and colleagues compared 16 weeks of slowvelocity resistance training to high-velocity power training in older women with selfreported disability (234). They noted significant improvements in dynamic balance and stair
climbing performance in both groups, but no differential effects of the two programs. Recent
studies have evaluated low-resistance (40% to 60% 1 RM) high-velocity power training on
measures of physical functioning (235-237). Orr and colleagues reported improvements in
measures of dynamic balance in older women and men in response to lower-intensity power
training when compared with a no-exercise control group (236). Both Miszko and colleages
Physical Activity Guidelines Advisory Committee Report G5–37
Part G. Section 5: Musculoskeletal Health
and Bottaro and colleagues. found that lower-intensity power training improved physical
functioning composite scores when compared with traditional slow-velocity resistance
training (235;237).
Summary
Exercise interventions targeted at improving lower-extremity muscle power in the elderly
have been well-tolerated, safe, and effective. Improvements in muscle power were generally
greater with interventions that emphasized high- versus low-velocity resistance training. In
addition, emerging evidence indicates that higher-velocity, lower-intensity resistance
training may improve physical functioning in older adults to a greater extent than traditional
slow-velocity resistance training.
Overall Summary
As this chapter amply demonstrates, physical activity has many benefits for musculoskeletal
health (for a detailed summary of these benefits, see Table E.1 in Section E: Integration
and Summary of the Science). Briefly, physical activity is inversely associated with risk of
hip and spine fracture. Exercise training can increase, or slow the decrease, in spine and hip
BMD, and can increase skeletal muscle mass, strength, power, and intrinsic neuromuscular
activation. In the absence of major joint injury, regular moderate-intensity physical activity
does not appear to promote the development of OA. In fact, physical activity may provide
protection against the development of OA, but there is limited evidence for this. In adults
with OA, participation in moderate-intensity, low-impact physical activity has diseasespecific benefits (e.g., pain, function, quality of life).
The musculoskeletal benefits of physical activity have been observed in adult women and
men across a wide age range, but information on race and ethnic specificity is lacking.
Moderate evidence supports a dose-response association of volume of physical activity with
hip fracture risk, and muscle mass and strength increase in an exercise intensity-dependent
manner. High-intensity and/or high-velocity resistance exercise may be particularly effective
in increasing BMD and muscle strength and power. Endurance exercise, even when
high-intensity in nature, has little effect on muscle mass and strength, but may preserve
BMD if the activities are weight-bearing. In the absence of major prior joint injury, regular
moderate- and vigorous-intensity physical activity in amounts that are commonly
recommended for general health benefits does not appear to increase the risk of developing
OA.
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