Fitness and Exercise Sourcebook Fitness amp Exercise Sourcebook

Part I: The Health Benefits of Physical Activity

Chapter 1—Physical Activity Has Many Health Benefits............ 3 Chapter 2—The Health Burden of Physical Inactivity............... 15 Chapter 3—Physical Activity and Life Satisfaction.................... 19 Chapter 4—Physical Activity and Disease Prevention............... 25

Section 4.1—Physical Fitness and

a Healthy Immune System ............ 26 Section 4.2—The Link Between Fitness

and Longevity in Older Adults....... 28 Section 4.3—The Link Between Mortality

and Physical Inactivity .................. 29 Section 4.4—Physical Activity Promotes

Bone Health .................................... 31

Section 4.5—The Effect of Physical Activity

on the Risk for Coronary

Chapter 5—Physical Activity and Mental Health..................... 37 Section 5.1—Physical Activity Helps

Control Stress............................. 38 Section 5.2—Exercise Fights Dementia.......... 40 Section 5.3—Physical Activity, Mood,

and Serious Mental Illness ........ 42 Chapter 6—Physical Activity and a Healthy Weight ................ 45

Section 6.1—Physical Activity for Weight Loss ................................ 46

Section 6.2—Exercise Does Not Over-Stimulate Appetite............ 49

Section 6.3—The Effect of Exercise on Metabolism ................................. 51

Chapter 7—Is Physical Inactivity Genetic?............................... 57

Part II: Guidelines for Lifelong Physical Fitness

Chapter 8—Prevalence of Self-Reported Physically Active Adults........................................................... 67

Chapter 9—Introduction to Fitness Guidelines ........................ 73 Chapter 10—Physical Fitness and Children ............................... 81

Section 10.1—Statistics on Physical Activity in Children.................... 82

Section 10.2—Physical Activity from Birth to Age Five ........................ 87

Section 10.3—Raising a Fit Preschooler........... 89 Section 10.4—Fitness Guidelines for

School-Aged Youth...................... 93

Section 10.5—Physical Fitness Education

in Schools .................................... 99 Chapter 11—Physical Fitness and Teenagers........................... 105

Section 11.3—Teenagers Exercising Far Less than Younger Kids ........................................... 112

Chapter 12—Promoting Physical Activity in Children and Teenagers ....................................................... 115

Section 12.1—Motivating Children and Teenagers to Be Active............. 116

Section 12.2—Fitness for Kids Who Don’t Like Sports...................... 120

Section 12.3—Tips on Promoting Physical

Fitness for Girls........................ 124 Chapter 13—Physical Fitness and Adults................................. 131

Section 13.1—Fitness Guidelines for Adults........................................ 132

Section 13.2—Daily Exercise Dramatically

Lowers Men’s Death Rates ...... 138 Section 13.3—Women, Physical Fitness,

and Heart Health ..................... 141

Section 13.4—Physical Activity for Pregnant

and Postpartum Women........... 144

Section 13.5—Research Shows Overweight

Women Improve Quality of Life through Exercise............... 146

Section 13.6—Statistics and Research on Women and Physical Activity...................................... 149

Chapter 14—Fitness for Mid-Life and Older Persons............... 159 Section 14.1—Exercise Program for

Mid-Life Persons ...................... 160 Section 14.2—Exercise for Menopause-

Aged Women ............................. 169 Chapter 15—Physical Fitness and the Elderly ......................... 171

Section 40.2—Sports Nutrition ....................... 450 Section 40.3—Top Sports Nutrition Myths..... 453

Chapter 41—Preventing Sports Injuries ................................... 457 Section 41.1—Common Sports Injuries

and Their Prevention ............... 458

Section 41.2—Sports-Related Concussions:

What You Need to Know to Be Safe ...................................... 466

Chapter 42—Preventing Sports Injuries for Child Athletes .... 471 Chapter 43—Fitness and Your Feet ........................................... 477 Chapter 44—Overtraining and Compulsive Exercise............... 481

Section 44.1—Overtraining in Women

and the Risk to Bone Health ....................................... 482

Section 44.2—Compulsive Exercise ................ 486 Chapter 45—Exercising Safely Outdoors .................................. 491

Section 45.1—Outdoor Exercise Safety .......... 492 Section 45.2—Air Pollution and Exercise ....... 495

Part VI: Physical Fitness for People with Health Conditions

Chapter 46—Introduction to Exercise with

a Health Condition ............................................... 501 Chapter 47—Physical Activity for People

with Disabilities.................................................... 505

Section 47.1—Increasing Physical Activity

for People with Disabilities...... 506

Section 47.2—Promoting Inclusive Physical

Activity Communities for People with Disabilities ........... 509

Preface

About This Book

Regular physical activity provides numerous health benefits, includ- ing a reduced risk of diabetes, osteoporosis, obesity, some cancers, and heart disease, as well as increased mental well-being, longevity, and life satisfaction. Beginning a physical fitness program is important at any age, and it can provide a lifelong love of fitness in children, increased strength and endurance in adults, and improved balance and flex- ibility in the elderly. Yet, according to the Centers for Disease Control and Prevention, almost 39% of Americans engage in no leisure-time physical activity.

Fitness and Exercise Sourcebook, Fourth Edition provides updated information about the health benefits of physical activity. It discusses the guidelines for physical activity in people of all ages and diverse fitness levels—including those with disabilities, chronic diseases, or other challenges. It describes ways to make exercise fun and offers suggestions for incorporating fitness into everyday activities. Ways to maintain motivation and set fitness goals are described, and different types of physical activity—including aerobic, strength, balance, and mind-body—are detailed. Information on safety concerns, nutrition and hydration, and equipment needs is included, and an end section offers a glossary of related terms and a directory of organizations that provide information about physical fitness and exercise.

How to Use This Book

This book is divided into parts and chapters. Parts focus on broad areas of interest. Chapters are devoted to single topics within a part.

Part I: The Health Benefits of Physical Activity details the consequences of inactivity and the health and mental benefits of physical activity, including life satisfaction, disease prevention, increased mental health, and a healthy weight. It also explores a possible genetic contribution to physical inactivity.

Part II: Guidelines for Lifelong Physical Fitness offers readers specific fitness suggestions, age-appropriate guidelines, and tips for promoting physical activity among children, teenagers, adults, mid-life persons, and the elderly. It concludes with a discussion of ways in which a com- munity’s environment can promote physical fitness.

Part III: Start Moving explores practical suggestions for adding activity to everyday life and for beginning an exercise program. It explains how to create a fitness plan, overcome barriers to exercise, find a fitness club or workout partners, and measure and track exercise intensity and calorie expenditure. It also evaluates the reality behind advertising claims exercise equipment manufacturers sometimes make.

Part IV: Exercise Basics includes facts about specific forms of exercise, from basics—such as aerobics and strength training—to individual ac- tivities—such as walking, biking, running, kickboxing, racquet sports, dancing, aquatic exercise, boot camp, and even the Wii. Mind-body ex- ercises, such as yoga and Pilates, are also discussed, and cross training, interval training, and power training are explained.

Part V: Fitness Safety offers suggestions about how to be safe during physical activity through warming up, avoiding common mistakes, choos- ing safe and comfortable equipment, eating and hydrating properly, and preventing sports injuries. It also discusses the risks of overtraining and compulsive exercise and offers tips for exercising safely out of doors.

Part VI: Physical Fitness for People with Health Conditions describes specific steps to physical fitness for people with disabilities, people who are overweight, and people with other health challenges, such as heart disease, bone disorders, breathing difficulties, diabetes, or cancer.

Part VII: Additional Help and Information includes a glossary of impor- tant terms and a directory of organizations able to provide information on physical fitness and exercise topics.

Bibliographic Note

This volume contains documents and excerpts from publications issued by the following U.S. government agencies: Centers for Disease Control and Prevention (CDC); Consumer Product Safety Commission (CPSC); National Cancer Institute (NCI); National Center for Comple- mentary and Alternative Medicine; National Heart, Lung, and Blood Institute (NHLBI); National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS); National Institute of Diabetes and Diges- tive and Kidney Diseases (NIDDK); National Institute on Aging (NIA); National Institutes of Health (NIH); President’s Council on Physical Fitness and Sports; U.S. Department of Health and Human Services (HHS); and U.S. Department of Homeland Security.

In addition, this volume contains copyrighted documents from the following organizations: Allergy and Asthma Network Mothers of Asth- matics; American College of Sports Medicine; American Council on Exercise; American Heart Association; American Orthopaedic Foot and Ankle Society; American Podiatric Medical Association; Ameri- can Psychological Association; Aquatic Exercise Association; Asthma and Allergy Foundation of America; Boys Town Pediatrics; Cleveland Clinic; ExRx.net; Government of Ontario Ministry of the Environment; Harvard Health Publications; Helpguide (Center for Healthy Aging); IDEA Health & Fitness Association; Indiana University Office of Uni- versity Communications; National Association for Sport and Physical Education; National Strength and Conditioning Association; Nemours Foundation; OrthoIndy; Oxford University Press; Rails-to-Trails Con- servancy; United States Professional Tennis Association; University of Michigan Health System; University of Oxford; Wisconsin Department of Health and Family Services; Wolters Kluwer Health; Women’s Sports Foundation; and World Health Organization (WHO).

Full citation information is provided on the first page of each chap- ter or section. Every effort has been made to secure all necessary rights to reprint the copyrighted material. If any omissions have been made, please contact Omnigraphics to make corrections for future editions.

Acknowledgements

Thanks go to the many organizations, agencies, and individuals who have contributed materials for this Sourcebook and to medical consultant Dr. David Cooke and document engineer Bruce Bellenir. Special thanks go to managing editor Karen Bellenir and research and permissions coordinator Liz Collins for their help and support.

About the Health Reference Series

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Part One

The Health Benefits

of Physical Activity

Chapter 1

Physical Activity Has Many Health Benefits

All Americans should be regularly physically active to improve over- all health and fitness and to prevent many adverse health outcomes. The benefits of physical activity occur in generally healthy people, in people at risk of developing chronic diseases, and in people with cur- rent chronic conditions or disabilities. This chapter gives an overview of research findings on physical activity and health.

Physical activity affects many health conditions, and the specific amounts and types of activity that benefit each condition vary. In de- veloping public health guidelines, the challenge is to integrate scientific information across all health benefits and identify a critical range of physical activity that appears to have an effect across the health benefits. One consistent finding from research studies is that once the health benefits from physical activity begin to accrue, additional amounts of activity provide additional benefits.

Although some health benefits seem to begin with as little as 60 minutes (1 hour) a week, research shows that a total amount of 150 minutes (2 hours and 30 minutes) a week of moderate-intensity aerobic activity, such as brisk walking, consistently reduces the risk of many chronic diseases and other adverse health outcomes.

Excerpted from “Chapter 2. Physical Activity Has Many Health Benefits,” Physical Activity Guidelines for Americans, U.S. Department of Health and Hu-

man Services (www.hhs.gov), October 16, 2008.

Fitness and Exercise Sourcebook, Fourth Edition

Examining the Relationship between Physical Activity and Health

In many studies covering a wide range of issues, researchers have focused on exercise, as well as on the more broadly defined concept of physical activity. Exercise is a form of physical activity that is planned, structured, repetitive, and performed with the goal of improving health or fitness. So, although all exercise is physical activity, not all physical activity is exercise.

Studies have examined the role of physical activity in many groups—men and women, children, teens, adults, older adults, people with disabilities, and women during pregnancy and the postpartum period. These studies have focused on the role that physical activity plays in many health outcomes, including the following:

•฀ Premature฀(early)฀death •฀ Diseases฀such฀as฀coronary฀heart฀disease,฀stroke,฀some฀cancers,฀

type 2 diabetes, osteoporosis, and depression •฀ Risk฀factors฀for฀disease,฀such฀as฀high฀blood฀pressure฀and฀high฀

blood cholesterol •฀ Physical฀fitness,฀such฀as฀aerobic฀capacity฀and฀muscle฀strength฀

and endurance •฀ Functional฀capacity฀(the฀ability฀to฀engage฀in฀activities฀needed฀for฀

daily living) •฀ Mental฀health,฀such฀as฀depression฀and฀cognitive฀function •฀ Injuries฀or฀sudden฀heart฀attacks

These studies have also prompted questions as to what type and how much physical activity is needed for various health benefits. To answer this question, investigators have studied three main kinds of physical activity: aerobic, muscle strengthening, and bone strengthen- ing. Investigators have also studied balance and flexibility activities.

Aerobic Activity

In this kind of physical activity (also called an endurance activity or cardio activity), the body’s large muscles move in a rhythmic man- ner for a sustained period of time. Brisk walking, running, bicycling, jumping฀rope,฀and฀swimming฀are฀all฀examples.฀Aerobic฀activity฀causes฀

a person’s heart to beat faster than usual.

Physical Activity Has Many Health Benefits

Aerobic physical activity has three components: •฀ Intensity,฀or฀how฀hard฀a฀person฀works฀to฀do฀the฀activity—the฀

intensities most often examined are moderate intensity (equiva- lent in effort to brisk walking) and vigorous intensity (equivalent in฀effort฀to฀running฀or฀jogging)

•฀ Frequency,฀or฀how฀often฀a฀person฀does฀aerobic฀activity •฀ Duration,฀or฀how฀long฀a฀person฀does฀an฀activity฀in฀any฀one฀session

Although these components make up a physical activity profile, research has shown that the total amount of physical activity (minutes of moderate-intensity physical activity, for example) is more important for achieving health benefits than is any one component (frequency, intensity, or duration).

Muscle-Strengthening Activity

This kind of activity, which includes resistance training and lifting weights, causes the body’s muscles to work or hold against an applied force฀or฀weight.฀These฀activities฀often฀involve฀relatively฀heavy฀objects,฀ such as weights, which are lifted multiple times to train various muscle groups. Muscle-strengthening activity can also be done by using elastic bands or body weight for resistance (climbing a tree or doing push-ups, for example).

Muscle-strengthening activity also has three components: •฀ Intensity,฀or฀how฀much฀weight฀or฀force฀is฀used฀relative฀to฀how฀

much a person is able to lift •฀ Frequency,฀or฀how฀often฀a฀person฀does฀muscle-strengthening฀ac-

tivity •฀ Repetitions,฀or฀how฀many฀times฀a฀person฀lifts฀a฀weight฀(analo-

gous to duration for aerobic activity) The effects of muscle-strengthening activity are limited to the

muscles฀doing฀the฀work.฀It’s฀important฀to฀work฀all฀the฀major฀muscle฀ groups of the body: the legs, hips, back, abdomen, chest, shoulders, and arms.

Bone-Strengthening Activity

This kind of activity (sometimes called weight-bearing or weight- loading activity) produces a force on the bones that promotes bone

Fitness and Exercise Sourcebook, Fourth Edition

growth and strength. This force is commonly produced by impact with the฀ground.฀Examples฀of฀bone-strengthening฀activity฀include฀jumping฀ jacks,฀running,฀brisk฀walking,฀and฀weight-lifting฀exercises.฀As฀these฀ examples illustrate, bone-strengthening activities can also be aerobic and muscle strengthening.

The Health Benefits of Physical Activity

Studies clearly demonstrate that participating in regular physical activity provides many health benefits. These benefits are summa- rized here. Many conditions affected by physical activity occur with increasing฀age,฀such฀as฀heart฀disease฀and฀cancer.฀Reducing฀the฀risk฀of฀ these conditions may require years of participation in regular physi- cal activity. However, other benefits, such as increased cardiorespira- tory fitness, increased muscular strength, and decreased depressive symptoms and blood pressure, require only a few weeks or months of participation in physical activity.

Health Benefits Associated with Regular Physical Activity

Children and Adolescents There is strong evidence for the following:

•฀ Improved฀cardiorespiratory฀and฀muscular฀fitness •฀ Improved฀bone฀health •฀ Improved฀cardiovascular฀and฀metabolic฀health฀biomarkers •฀ Favorable฀body฀composition

There is moderate evidence for reduced symptoms of depression. Adults and Older Adults

There is strong evidence for the following: •฀ Lower฀risk฀of฀early฀death •฀ Lower฀risk฀of฀coronary฀heart฀disease •฀ Lower฀risk฀of฀stroke •฀ Lower฀risk฀of฀high฀blood฀pressure •฀ Lower฀risk฀of฀adverse฀blood฀lipid฀profile •฀ Lower฀risk฀of฀type฀2฀diabetes

Physical Activity Has Many Health Benefits

•฀ Lower฀risk฀of฀metabolic฀syndrome •฀ Lower฀risk฀of฀colon฀cancer •฀ Lower฀risk฀of฀breast฀cancer •฀ Prevention฀of฀weight฀gain •฀ Weight฀loss,฀particularly฀when฀combined฀with฀reduced฀calorie฀

intake •฀ Improved฀cardiorespiratory฀and฀muscular฀fitness •฀ Prevention฀of฀falls •฀ Reduced฀depression •฀ Better฀cognitive฀function฀(for฀older฀adults)

There is moderate to strong evidence for the following: •฀ Better฀functional฀health฀(for฀older฀adults) •฀ Reduced฀abdominal฀obesity

There is moderate evidence for the following: •฀ Lower฀risk฀of฀hip฀fracture

•฀ Lower฀risk฀of฀lung฀cancer •฀ Lower฀risk฀of฀endometrial฀cancer •฀ Weight฀maintenance฀after฀weight฀loss •฀ Increased฀bone฀density •฀ Improved฀sleep฀quality

Note: The Advisory Committee rated the evidence of health benefits of physical activity as strong, moderate, or weak. To do so, the com- mittee considered the type, number, and quality of studies available, as well as consistency of findings across studies that addressed each outcome. The committee also considered evidence for causality and dose response in assigning the strength-of-evidence rating.

The Beneficial Effects of Increasing Physical Activity: It’s About Overload, Progression, and Specificity

Overload is the physical stress placed on the body when physi- cal activity is greater in amount or intensity than usual. The body’s structures฀and฀functions฀respond฀and฀adapt฀to฀these฀stresses.฀For฀

Fitness and Exercise Sourcebook, Fourth Edition

example, aerobic physical activity places a stress on the cardiorespi- ratory system and muscles, requiring the lungs to move more air and the heart to pump more blood and deliver it to the working muscles. This increase in demand increases the efficiency and capacity of the lungs, heart, circulatory system, and exercising muscles. In the same way, muscle-strengthening and bone-strengthening activities overload muscles and bones, making them stronger.

Progression is closely tied to overload. Once a person reaches a certain fitness level, he or she progresses to higher levels of physi- cal activity by continued overload and adaptation. Small, progressive changes in overload help the body adapt to the additional stresses while฀minimizing฀the฀risk฀of฀injury.

Specificity means that the benefits of physical activity are specific to

the฀body฀systems฀that฀are฀doing฀the฀work.฀For฀example,฀aerobic฀physi- cal activity largely benefits the body’s cardiovascular system.

The health benefits of physical activity are seen in children and adolescents, young and middle-aged adults, older adults, women and men, people of different races and ethnicities, and people with disabili- ties and chronic conditions. The health benefits of physical activity are generally independent of body weight. Adults of all sizes and shapes gain health and fitness benefits by being habitually physically active. The฀benefits฀of฀physical฀activity฀also฀outweigh฀the฀risk฀of฀injury฀and฀ sudden heart attacks, two concerns that prevent many people from becoming physically active.

The following sections provide more detail on what is known from research studies about the specific health benefits of physical activity and how much physical activity is needed to get the health benefits.

Premature Death

Strong scientific evidence shows that physical activity reduces the risk of premature death (dying earlier than the average age of death for a specific population group) from the leading causes of death, such as heart disease and some cancers, as well as from other causes of death. This effect is remarkable in two ways:

•฀ First,฀only฀a฀few฀lifestyle฀choices฀have฀as฀large฀an฀effect฀on฀mor-

tality as physical activity. It has been estimated that people who are physically active for approximately 7 hours a week have a 40% lower risk of dying early than those who are active for less than 30 minutes a week.

Physical Activity Has Many Health Benefits

•฀ Second,฀it฀is฀not฀necessary฀to฀do฀high฀amounts฀of฀activity฀or฀

vigorous-intensity activity to reduce the risk of premature death. Studies show substantially lower risk when people do 150 minutes of at least moderate-intensity aerobic physical activity a week.

Research฀clearly฀demonstrates฀the฀importance฀of฀avoiding฀inactivity.฀ Even low amounts of physical activity reduce the risk of dying prema- turely. The most dramatic difference in risk is seen between those who are inactive (30 minutes a week) and those with low levels of activity (90 minutes or 1 hour and 30 minutes a week). The relative risk of dying prematurely continues to be lower with higher levels of reported moderate- or vigorous-intensity leisure-time physical activity.

All adults can gain this health benefit of physical activity. Age, race, and ethnicity do not matter. Men and women younger than 65 years as well as older adults have lower rates of early death when they are physically active than when they are inactive. Physically active people of all body weights (normal weight, overweight, obese) also have lower rates of early death than do inactive people.

Cardiorespiratory Health

The benefits of physical activity on cardiorespiratory health are some of the most extensively documented of all the health benefits. Cardiorespiratory health involves the health of the heart, lungs, and blood vessels.

Heart diseases and stroke are two of the leading causes of death in the฀United฀States.฀Risk฀factors฀that฀increase฀the฀likelihood฀of฀cardio- vascular diseases include smoking, high blood pressure (called hyper- tension), type 2 diabetes, and high levels of certain blood lipids (such as฀low-density฀lipoprotein,฀or฀LDL,฀cholesterol).฀Low฀cardiorespiratory฀ fitness also is a risk factor for heart disease.

People who do moderate- or vigorous-intensity aerobic physical activity have a significantly lower risk of cardiovascular disease than do฀inactive฀people.฀Regularly฀active฀adults฀have฀lower฀rates฀of฀heart฀ disease and stroke and have lower blood pressure, better blood lipid profiles, and greater levels of fitness. Significant reductions in risk of cardiovascular disease occur at activity levels equivalent to 150 minutes a week of moderate-intensity physical activity. Even greater benefits are seen with 200 minutes (3 hours and 20 minutes) a week. The evidence is strong that greater amounts of physical activity result in even further reductions in the risk of cardiovascular disease.

Everyone can gain the cardiovascular health benefits of physi- cal activity. The amount of physical activity that provides favorable

Fitness and Exercise Sourcebook, Fourth Edition

cardiorespiratory health and fitness outcomes is similar for adults of various ages, including older people, as well as for adults of various races and ethnicities. Aerobic exercise also improves cardiorespiratory fitness in individuals with some disabilities, including people who have lost the use of one or both legs and those with multiple sclerosis, stroke, spinal฀cord฀injury,฀and฀cognitive฀disabilities.

Moderate-intensity physical activity is safe for generally healthy women during pregnancy. It increases cardiorespiratory fitness with- out increasing the risk of early pregnancy loss, preterm delivery, or low birth weight. Physical activity during the postpartum period also improves cardiorespiratory fitness.

Metabolic Health

Regular฀physical฀activity฀strongly฀reduces฀the฀risk฀of฀developing฀ type 2 diabetes as well as the metabolic syndrome. The metabolic syn- drome is defined as a condition in which people have some combina- tion of high blood pressure, a large waistline (abdominal obesity), an adverse฀blood฀lipid฀profile฀(low฀levels฀of฀high-density฀lipoprotein฀[HDL]฀ cholesterol, raised triglycerides), and impaired glucose tolerance.

People who regularly engage in at least moderate-intensity aerobic activity have a significantly lower risk of developing type 2 diabetes than do inactive people. Although some experts debate the useful- ness of defining the metabolic syndrome, good evidence exists that physical activity reduces the risk of having this condition, as defined in฀various฀ways.฀Lower฀rates฀of฀these฀conditions฀are฀seen฀with฀120฀to฀ 150 minutes (2 hours to 2 hours and 30 minutes) a week of at least moderate-intensity aerobic activity. As with cardiovascular health, ad- ditional levels of physical activity seem to lower risk even further. In addition, physical activity helps control blood glucose levels in persons who already have type 2 diabetes.

Physical activity also improves metabolic health in youth. Studies find this effect when young people participate in at least three days of vigorous aerobic activity a week. More physical activity is associated with improved metabolic health, but research has yet to determine the exact amount of improvement.

Obesity and Energy Balance

Overweight and obesity occur when fewer calories are expended, including calories burned through physical activity, than are taken in through food and beverages. Physical activity and caloric intake both must

be considered when trying to control body weight. Because of this role in

Physical Activity Has Many Health Benefits

energy balance, physical activity is a critical factor in determining wheth- er a person can maintain a healthy body weight, lose excess body weight, or maintain successful weight loss. People vary a great deal in how much physical activity they need to achieve and maintain a healthy weight. Some need more physical activity than others to maintain a healthy body weight, to lose weight, or to keep weight off once it has been lost.

Strong scientific evidence shows that physical activity helps people maintain a stable weight over time. However, the optimal amount of physical activity needed to maintain weight is unclear. People vary greatly in how much physical activity results in weight stability. Many people need more than the equivalent of 150 minutes of moderate- intensity activity a week to maintain their weight.

Over short periods of time, such as a year, research shows that it is possible to achieve weight stability by doing the equivalent of 150 to 300 minutes (5 hours) a week of moderate-intensity walking at about a four-mile-an-hour pace. Muscle-strengthening activities may help promote weight maintenance, although not to the same degree as aerobic activity.

People who want to lose a substantial (more than 5% of body weight) amount of weight and people who are trying to keep a significant amount of weight off once it has been lost need a high amount of physi- cal activity unless they also reduce their caloric intake. Many people need to do more than 300 minutes of moderate-intensity activity a week to meet weight-control goals.

Regular฀physical฀activity฀also฀helps฀control฀the฀percentage฀of฀body฀fat฀ in children and adolescents. Exercise training studies with overweight and obese youth have shown that they can reduce their body fatness by participating in physical activity that is at least moderate intensity on three to five days a week, for 30 to 60 minutes each time.

Musculoskeletal Health

Bones,฀muscles,฀and฀joints฀support฀the฀body฀and฀help฀it฀move.฀ Healthy฀bones,฀joints,฀and฀muscles฀are฀critical฀to฀the฀ability฀to฀do฀ daily activities without physical limitations.

Preserving฀bone,฀joint,฀and฀muscle฀health฀is฀essential฀with฀increas- ing age. Studies show that the frequent decline in bone density that happens during aging can be slowed with regular physical activity. These effects are seen in people who participate in aerobic, muscle- strengthening, and bone-strengthening physical activity programs of moderate or vigorous intensity. The range of total physical activity for these benefits varies widely. Important changes seem to begin at 90 minutes a week and continue up to 300 minutes a week.

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Hip fracture is a serious health condition that can have life-changing negative effects for many older people. Physically active people, es- pecially women, appear to have a lower risk of hip fracture than do inactive฀people.฀Research฀studies฀on฀physical฀activity฀to฀prevent฀hip฀ fracture show that participating in 120 to 300 minutes a week of physi- cal activity that is of at least moderate intensity is associated with a reduced risk. It is unclear, however, whether activity also lowers risk of fractures of the spine or other important areas of the skeleton.

Building strong, healthy bones is also important for children and adolescents. Along with having a healthy diet that includes adequate calcium and vitamin D, physical activity is critical for bone develop- ment in children and adolescents. Bone-strengthening physical activity done three or more days a week increases bone-mineral content and bone density in youth.

Regular฀physical฀activity฀also฀helps฀people฀with฀arthritis฀or฀other฀ rheumatic฀conditions฀affecting฀the฀joints.฀Participation฀in฀130฀to฀150฀ minutes (2 hours and 10 minutes to 2 hours and 30 minutes) a week of moderate-intensity, low-impact physical activity improves pain man- agement,฀function,฀and฀quality฀of฀life.฀Researchers฀don’t฀yet฀know฀ whether participation in physical activity, particularly at low to mod- erate intensity, reduces the risk of osteoarthritis. Very high levels of physical activity, however, may have extra risks. People who participate in very high levels of physical activity, such as elite or professional athletes, have a higher risk of hip and knee osteoarthritis, mostly due to฀the฀risk฀of฀injury฀involved฀in฀competing฀in฀some฀sports.

Progressive muscle-strengthening activities increase or preserve muscle mass, strength, and power. Higher amounts (through greater frequency or higher weights) improve muscle function to a greater degree.฀Improvements฀occur฀in฀younger฀and฀older฀adults.฀Resistance฀ exercises also improve muscular strength in persons with such condi- tions฀as฀stroke,฀multiple฀sclerosis,฀cerebral฀palsy,฀spinal฀cord฀injury,฀ and cognitive disability. Though it doesn’t increase muscle mass in the same way that muscle-strengthening activities do, aerobic activity may also help slow the loss of muscle with aging.

Functional Ability and Fall Prevention

Functional฀ability฀is฀the฀capacity฀of฀a฀person฀to฀perform฀tasks฀or฀ behaviors that enable him or her to carry out everyday activities, such as฀climbing฀stairs฀or฀walking฀on฀a฀sidewalk.฀Functional฀ability฀is฀key฀to฀

a person’s ability to fulfill basic life roles, such as personal care, grocery shopping,฀or฀playing฀with฀his฀or฀her฀grandchildren.฀Loss฀of฀functional฀ ability is referred to as functional limitation.

Physical Activity Has Many Health Benefits

Middle-aged and older adults who are physically active have lower risk of functional limitations than do inactive adults. It appears that greater physical activity levels can further reduce risk of functional limitations.

Older adults who already have functional limitations also benefit from regular physical activity. Typically, studies of physical activity in adults with functional limitations tested a combination of aerobic and muscle strengthening activities, making it difficult to assess the relative importance of each type of activity. However, both types of activity appear to provide benefit.

In older adults at risk of falls, strong evidence shows that regular physical฀activity฀is฀safe฀and฀reduces฀this฀risk.฀Reduction฀in฀falls฀is฀seen฀ for participants in programs that include balance and moderate-intensity muscle-strengthening activities for 90 minutes a week plus moderate- intensity walking for about an hour a week. It’s not known whether dif- ferent combinations of type, amount, or frequency of activity can reduce falls to a greater degree. Tai chi exercises also may help prevent falls.

Cancer

Physically active people have a significantly lower risk of colon cancer than do inactive people, and physically active women have a significantly฀lower฀risk฀of฀breast฀cancer.฀Research฀shows฀that฀a฀wide฀ range of moderate-intensity physical activity—between 210 and 420 minutes a week (3 hours and 30 minutes to 7 hours)—is needed to significantly reduce the risk of colon and breast cancer; currently, 150 minutes฀a฀week฀does฀not฀appear฀to฀provide฀a฀major฀benefit.฀It฀also฀ appears that greater amounts of physical activity lower risks of these cancers even further, although exactly how much lower is not clear.

Although not definitive, some research suggests that the risk of endometrial cancer in women and lung cancers in men and women also may be lower among those who are regularly active compared to those who are inactive.

Finally,฀cancer฀survivors฀have฀a฀better฀quality฀of฀life฀and฀improved฀ physical fitness if they are physically active, compared to survivors who are inactive.

Mental Health

Physically active adults have lower risk of depression and cognitive decline฀(declines฀with฀aging฀in฀thinking,฀learning,฀and฀judgment฀skills).฀ Physical฀activity฀also฀may฀improve฀the฀quality฀of฀sleep.฀Whether฀physi- cal activity reduces distress or anxiety is currently unclear.

Fitness and Exercise Sourcebook, Fourth Edition

Mental health benefits have been found in people who do aerobic or a combination of aerobic and muscle-strengthening activities three to five days a week for 30 to 60 minutes at a time. Some research has shown that even lower levels of physical activity also may provide some benefits.

Regular฀physical฀activity฀appears฀to฀reduce฀symptoms฀of฀anxiety฀ and฀depression฀for฀children฀and฀adolescents.฀Whether฀physical฀activity฀ improves self-esteem is not clear.

Adverse Events

Some people hesitate to become active or increase their level of physical฀activity฀because฀they฀fear฀getting฀injured฀or฀having฀a฀heart฀ attack. Studies of generally healthy people clearly show that moderate- intensity physical activity, such as brisk walking, has a low risk of such adverse events.

The฀risk฀of฀musculoskeletal฀injury฀increases฀with฀the฀total฀amount฀ of฀physical฀activity.฀For฀example,฀a฀person฀who฀regularly฀runs฀40฀miles฀ a฀week฀has฀a฀higher฀risk฀of฀injury฀than฀a฀person฀who฀runs฀10฀miles฀ each week. However, people who are physically active may have fewer injuries฀from฀other฀causes,฀such฀as฀motor฀vehicle฀collisions฀or฀work- related฀injuries.฀Depending฀on฀the฀type฀and฀amount฀of฀activity฀that฀ physically฀active฀people฀do,฀their฀overall฀injury฀rate฀may฀be฀lower฀than฀ the฀overall฀injury฀rate฀for฀inactive฀people.

Participation in contact or collision sports, such as soccer or football, has฀a฀higher฀risk฀of฀injury฀than฀participation฀in฀noncontact฀physical฀ activity, such as swimming or walking. However, when performing the same฀activity,฀people฀who฀are฀less฀fit฀are฀more฀likely฀to฀be฀injured฀than฀ people who are fitter.

Cardiac events, such as a heart attack or sudden death during physical activity, are rare. However, the risk of such cardiac events does increase when a person suddenly becomes much more active than usual. The greatest risk occurs when an adult who is usually inactive engages in vigorous-intensity activity (such as shoveling snow). People who are regularly physically active have the lowest risk of cardiac events both while being active and overall.

The bottom line is that the health benefits of physical activity far outweigh the risks of adverse events for almost everyone.

Chapter 2

The Health Burden of Physical Inactivity

Facts

•฀ Appropriate฀regular฀physical฀activity฀is฀a฀major฀component฀in฀ preventing the growing global burden of chronic disease.

•฀ At฀least฀60%฀of฀the฀global฀population฀fails฀to฀achieve฀the฀mini-

mum recommendation of 30 minutes moderate intensity physi- cal activity daily.

•฀ The฀risk฀of฀getting฀a฀cardiovascular฀disease฀increases฀by฀1.5฀

times in people who do not follow minimum physical activity

recommendations. •฀ Inactivity฀greatly฀contributes฀to฀medical฀costs—by฀an฀estimated฀

$75 billion in the United States in 2000 alone. •฀ Increasing฀physical฀activity฀is฀a฀societal,฀not฀just฀an฀individual,฀

problem and demands a population-based, multi-sectoral, multi- disciplinary, and culturally relevant approach.

Appropriate฀regular฀daily฀physical฀activity฀is฀a฀major฀component฀in฀ preventing chronic disease, along with a healthy diet and not smoking. For฀individuals,฀it฀is฀a฀powerful฀means฀of฀preventing฀chronic฀diseases;฀ for nations, it can provide a cost-effective way of improving public

“Physical Activity,” http://www.who.int/dietphysicalactivity/media/en/ gsfs_pa.pdf.฀©฀2003฀World฀Health฀Organization.฀Reprinted฀with฀permission.฀ ฀Reviewed฀by฀David฀A.฀Cooke,฀MD,฀FACP,฀March฀2010.

Fitness and Exercise Sourcebook, Fourth Edition

health across the population. Available experience and scientific evi- dence show that regular physical activity provides people, both male and female, of all ages and conditions—including disabilities—with

a wide range of physical, social, and mental health benefits. Physical activity interacts positively with strategies to improve diet, discourage the use of tobacco, alcohol, and drugs, helps reduce violence, enhances functional capacity, and promotes social interaction and integration.

Extent of the Problem

Physical inactivity was estimated to cause 1.9 million deaths world- wide annually, according to World Health Report [WHR] 2002. Globally, it is estimated to cause about 10–16% of cases each of breast cancer, colon cancers, and diabetes, and about 22% of ischemic heart disease. Estimated attributable fractions are similar in men and women. Op- portunities฀for฀people฀to฀be฀physically฀active฀exist฀in฀the฀four฀major฀ domains of their day. These are:

•฀ at฀work฀(whether฀or฀not฀the฀work฀involves฀manual฀labor); •฀ for฀transport฀(walking฀or฀cycling฀to฀work,฀to฀shop,฀etc.); •฀ during฀domestic฀duties฀(housework,฀gathering฀fuel,฀etc.); •฀ in฀leisure฀time฀(sports฀and฀recreational฀activities).

The global estimate for the prevalence of physical inactivity among adults is 17%. Estimates for prevalence of some, but insufficient, activity (<2.5 hours per week of moderate activity) ranged from 31% to 51%, with

a global average of 41% across the sub-regions. WHR 2002 used a number of direct and indirect data sources and a range of survey instruments and methodologies to estimate activity levels in these four domains. The most data was available for leisure time activity, with less direct data avail- able on occupational activity, and little direct data available for activity related to transport and domestic tasks. In addition, the WHR 2002 data only estimates the prevalence of physical inactivity among people aged 15 years and over, which suggests the total figures could be higher. Physical activity declines with age, falling off from adolescence, and physical activ- ity and physical education is declining in schools worldwide. Inactivity is generally higher amongst girls and women.

Why Is Regular Physical Activity Necessary?

Physical inactivity, along with other key risk factors, is a significant contributor฀to฀the฀global฀burden฀of฀chronic฀disease.฀Regular฀physical฀

The Health Burden of Physical Inactivity

activity reduces the risk of heart disease, stoke, and breast and colon cancers. These benefits are mediated through a number of mechanisms. In general, physical activity improves glucose metabolism, reduces body fat, and lowers blood pressure; these are the main ways in which it฀is฀thought฀to฀reduce฀the฀risk฀of฀CVD฀[cardiovascular฀disease]฀and฀ diabetes. It can also help manage and mitigate the effects of these diseases. Physical activity may also reduce the risk of colon cancer by its effects on prostaglandins, reduced intestinal transit time, and higher antioxidant levels.

Physical activity is associated with a lower risk of breast cancer, which may be the result of effects on hormonal metabolism. Partici- pation in physical activity can also improve musculoskeletal health, control body weight, and reduce symptoms of depression. The possible beneficial effects on musculoskeletal conditions such as lower back pain, osteoporosis, and falls, as well as on obesity, depression, anxiety, and stress, have been well reported in a number of studies. Beyond the direct medical benefits, increasing physical activity through an inte- grated program, which takes into account transportation and urban planning policy, makes other broader contributions, increasing social interaction฀throughout฀the฀life฀course,฀providing฀recreational฀enjoy- ment, and reducing violence, urban traffic congestion, and pollution.

Physical activity also has economic benefits, especially in terms of reduced health care costs, increased productivity, and healthier physi- cal and social environments. Data from developed countries indicate that the direct costs of inactivity are enormous. The costs associated with inactivity and obesity accounted for some 9.4% of the national U.S. health expenditure in 1995. Physically active individuals in the United States save an estimated $500 per year in health care costs ac- cording to 1998 data. Inactivity alone may have contributed as much as $75 billion to U.S. medical costs in the year 2000. In Canada, physical inactivity accounts for about 6% of total health care costs.

What Can We Do about It?

While฀different฀amounts฀are฀needed฀for฀various฀outcomes,฀the฀opti- mal combination of type, frequency, and intensity for different popula- tions is not known. There is, however, clear consensus in recommending at least 30 minutes daily of moderate intensity activity. Increased benefits come from doing more, especially more vigorous activities, and these are highly recommended for youth to support healthy bones and muscles. Physical activity does not necessarily mean running a strenuous฀marathon฀or฀playing฀competitive฀sports.฀Rather,฀for฀many฀

Fitness and Exercise Sourcebook, Fourth Edition