PHYSICAL ACTIVITY

Exercise, sport, play, games, dance—these and many other terms have been used to describe the wide variety of pursuits considered to be physical activity. "Physical activity" is a universal term defined as "bodily movement that is produced by the contraction of skeletal muscles and that substantially increases the amount of energy you expend" (USDHHS, 1996). "Exercise" is narrower in focus and is defined as "one type of physical activity conducted with the intent of developing physical fitness" (Corbin and Pangrazi, 1998). The term is typically used for calisthenics, resistance exercises, stretching exercises designed for flexibility, and aerobic exercises specifically designed to improve cardiovascular fitness. Sport, play, games, dance, and recreational activities are all different forms of physical activity, some more organized than others.

PHYSICAL ACTIVITY: A BRIEF HISTORY

Throughout history, the importance of physical activity to health and fitness has been acknowledged as an important component of life, along with work, play, and social, religious, and cultural activities. The early Greeks knew the importance of a sound body to hardy spirits and tough minds. The Olympics exemplify the place of prominence they afforded to physical activity. Hippocrates, generally known as the father of medicine, expressed interest in the hygienic value of exercise. As early as 3000 to 1000 b.c.e. the Chinese described the principle of human harmony, a concept that valued the role of physical activity. Various Native American and African groups also have featured active lifestyles and physical activity prominently in their cultures.

Early Europeans also knew the value of regular physical activity. In the seventeenth century, John Dryden (1631–1700) wrote: "Better to hunt in fields, for health unbought, than fee the doctor for nauseous draught; the wise, for cure, on exercise depend; God never made his work for man to mend" (Paffenbarger and Hyde, 1980). By the late 1800s, the General Hygiene movement had begun. Physical activity in the United States was championed in the late 1880s by physicians— many who were greatly influenced by their European heritage—who focused on promoting exercise programs in schools with the intent of improving health. These programs, later referred to as physical education, were the principal sources of public efforts to promote physical activity in the late nineteenth and early twentieth century. From 1900 through the mid-1950s a primary reason for the promotion of physical activity (exercise) was to prepare men for war. During this same time there was an increased emphasis on school sports, with an emphasis on college athletic programs. Physical activity, as a social phenomenon, was principally an endeavor for males, however.

In 1956, President Dwight D. Eisenhower established the President's Council on Youth Fitness, a cabinet-level agency, reflecting a growing concern for the lack of fitness among American youth, specifically a concern that many youth were considered unfit for war. In 1957, the American Medical Association joined in the public effort by endorsing the president's new council. For much of the mid–twentieth century, youth fitness and physical activity were the focus of public attention.

The year 1960 is generally considered to be when the "physical fitness boom" began in the United States. It was during this period that the American College of Sports Medicine (ASCM) was founded and Dr. Kenneth Cooper's book Aerobics (1968) was published. These two events did much to make Americans aware of the health benefits of physical activity. In 1961, Hans Kraus and Wilhelm Raab published the book Hypokinetic Disease, which many consider to be a landmark publication linking disease to physical inactivity. Hypokinetic diseases (health problems associated with inactive lifestyles) became a topic for increased study by the medical and research communities. From 1950 through the 1980s the study of physical activity epidemiology led researchers to conclude that there was evidence "that the relationship between exercise and good health is more than circumstantial. If some questions are not yet answered, they are far less important than those that have been" (Paffenbarger and Hyde, 1980). In 1996, Physical Activity and Health: A Report of the Surgeon General synthesized the mounting evidence that physical activity and good health are inextricably linked.

PHYSICAL ACTIVITY PATTERNS IN MODERN CULTURE

The human organism is designed to be physically active. Anthropologists indicate that the need to be active is associated with our need to find food, fight predators, and to flee for safety. While the "fight or flight" response that prepares people for physical activity still exists, automation and technology have freed many from the heavy physical labor that was characteristic of previous generations. The American workweek decreased from 70 hours in 1860 to less than 40 hours in the year 2000. Baseline data for the national health goals for the year 2010 indicate that 40 percent of the adults eighteen years of age and older do no regular leisure time activity. Approximately 23 percent of adults in the United States report regular vigorous physical activity (20 minutes or more 3 days a week) and only 15 percent report moderate physical activity equal to brisk walking (30 minutes on at least 5 days a week). Health goals for 2010 outline the need to increase these proportions— by 15 to 30 percent for vigorous activity and 23 to 30 percent for moderate activity—and to reduce sedentary behaviors from 40 percent to 20 percent. Goals are also outlined for increasing participation in physical activities such as resistance training for muscle fitness and stretching for developing flexibility.

Also apparent is the decline in physical activity from childhood to adulthood. Sedentary behavior is almost nonexistent among young children (about 6 percent for boys and 8 percent for girls) but increases to more than 20 percent by age twenty (22 percent for males and 25 percent for females). Vigorous activity decreases from 71 percent for boys and 66 percent for girls at age twelve to 43 percent for males and 28 percent for females at age twenty. Moderate activity levels decrease from 39 percent for boys and 32 percent for girls at age twelve to 22 percent for males and 21 percent for females at age twenty.

Different segments of the population are more active than others. Beginning in childhood and continuing throughout life, males are more active than females, with differences varying depending on the type of activity. Disparities in activity levels are also apparent for various ethnic groups. African Americans, Hispanics, and Native Americans, for example, are typically less active than non-Hispanic whites. To some extent these differences are influenced by education and socioeconomic status. Low socioeconomic groups with low education levels are less likely to be active than middle and high socioeconomic groups with higher education levels. The fact that minority populations are underrepresented in the upper socioeconomic and upper education levels could account for some of the differences in activity levels among ethnic groups.

PHYSICAL ACTIVITY AND HEALTH

Medical progress in preventing and treating infectious disease resulted in major changes in the causes of death between 1900 and 2000. Pneumonia, tuberculosis, and diarrhea were the three most common causes of death in 1900. In 2000, in developed countries, the leading causes of death were heart disease, cancer, and stroke. Large long-term public health studies began to focus on these chronic diseases by the mid-1900s, and by the 1960s several major studies had been published establishing physical inactivity as an important contributor to chronic conditions, especially heart disease. Some of the more prominent studies showed that people in active occupations, such as bus conductors in London, postal workers who delivered the mail, and longshoreman who did hard physical labor, were less likely to have heart attacks and other related heart conditions than bus drivers, postal clerks who sorted the mail, and white-collar workers who did little physical activity on the job.

The wealth of evidence led the Surgeon General of the United States to note: "Many Americans may be surprised at the extent and strength of the evidence linking physical activity to numerous health improvements. Most significantly, regular physical activity greatly reduces the risk of dying of coronary heart disease, the leading cause of death in the United States. Physical activity also reduces the risk of developing diabetes, hypertension, and colon cancer; enhances feelings of general wellbeing; is important for healthy bones and joints; and helps maintain function and preserves independence in older adults" (Corbin and Pangrazi, 1999). Table 1 synthesizes the findings of the research through the year 2000, as accumulated from a variety of sources.

Prior to 1960, little attention had been focused on the amount of physical activity necessary to produce health benefits. With the fitness boom in the 1960s, researchers began more intense efforts to find out "how much physical activity is enough," though the focus was primarily on how much is enough for improved fitness and physical performance, rather than on the health benefits of activity. The research, initially prompted by coaches interested in enhancing the performance of athletes, led to the development of guidelines based on the frequency, intensity, and duration of activity necessary to improve fitness for performance. By the 1970s, the focus on high intensity and short duration activity was firmly established. In 1972, the American Heart Association (AHA) published an exercise testing and training handbook and, in 1975, the American College of Sports Medicine (ACSM) published its first set of guidelines outlining the frequency, intensity, duration, and mode of exercise necessary to produce physical fitness.

The focus on exercise for fitness and performance began to change with the accumulation of public health research outlining the health benefits of activity. The evidence that accumulated in the last half of the twentieth century resulted in new guidelines in the 1990s. In July 1992, the AHA, in cooperation with ACSM, the Centers for Disease Prevention and Control (CDC), and the President's Council of Physical Fitness and Sports, issued a statement acknowledging the importance of lifestyle physical activity as a means of reducing

Table 1

disease risk. The recommendations focused on accumulating thirty minutes (or more) of moderate physical activity throughout the day over the course of most days of the week. Examples of such activities are walking up stairs (instead of taking the elevator), gardening, raking leaves, dancing, and walking all or part of the way to work. Activity can also be planned exercise or recreation such as jogging, playing tennis, swimming, and cycling.

Based on the accumulating evidence, Blair and colleagues (1993) suggested the need for a shift from the strategy of exercise for fitness to a new strategy of physical activity for public health. This new strategy, sometimes referred to as the "lifetime physical activity strategy," differs from earlier strategies in three ways. First, the new strategy focuses on the amount of physical activity necessary to produce health benefits associated with reduced morbidity and mortality rather than fitness or performance benefits. Second, the new strategy focuses on moderate activity rather than the vigorous physical activity of the old strategy designed to enhance fitness and performance. Finally, the new strategy emphasizes the value of accumulating physical activity throughout the day, as opposed to having to perform the activity in a single bout.

THE PHYSICAL ACTIVITY PYRAMID

The 2000 exercise and prescription guidelines of the ACSM acknowledged the new strategy of physical activity for health. The FIT (frequency, intensity, time or duration) formula for various types of physical activity was adjusted to include more moderate activity that results in specific health benefits. The Physical Activity Pyramid (see Figure1) illustrates the FIT formula for six different types of physical activity, each with its own unique benefits. The Physical Activity Pyramid is modeled after the Food Guide Pyramid developed by the United States Department of Agriculture.

At the base of the pyramid (Level 1) is lifestyle physical activity. Lifestyle physical activities are those people can do as part of their regular workday or daily routine. Examples of such activities are yard work and delivering the mail. A person who works while sitting at a desk for most of the day can get lifestyle activity by walking or riding a bicycle to work rather than driving a car, or by walking up the stairs at work rather than taking an elevator. Those who are totally sedentary should focus on this level of the pyramid because moderate amounts of physical activity can provide many of the health benefits outlined in Figure 1. As the 1996 Surgeon General's Report states, "something is better than nothing," and a good start would be thirty minutes of lifestyle physical activity on most days of the week.

Level 2 of the pyramid includes active aerobic activities. Aerobic activities are those performed at a pace for which the body can supply adequate oxygen to meet the demands of the activity. Because lifestyle activities meet this criterion, they are aerobic in nature. In the pyramid, however, active aerobics refers to those aerobic activities that elevate the heart rate to an appropriate target heart rate. This level includes aerobic activities using the FIT formula based on target heart rate (elevating the heart rate to an appropriate intensity at least three days a week for a time of at least 20 minutes). Examples of popular moderate to vigorous active aerobics are aerobic dance, step aerobics, jogging, moderate to vigorous swimming, and biking. Because they are more vigorous than activities at Level 1, active aerobics can be performed less frequently and the time of each activity bout can be shorter.

Also on Level 2 of the pyramid are active sports and recreational activities. Some examples of active sports are basketball, tennis, hiking, racquetball, and volleyball. Like active aerobics, this type of activity is typically more vigorous than lifestyle physical activity. Sports involve vigorous bursts of activity with brief rest periods. Though they are often not truly aerobic in nature, when they are done without long rest periods they have many of the same benefits as aerobic activities. The FIT formula for active sports and recreation is similar to the formula for active aerobics.

Some sports are not vigorously active and should be considered lifestyle physical activities. For example, golf, as a physical activity, is similar to walking to work, rather than the more vigorous activity generated in tennis or basketball—it is beneficial, but not vigorous in nature. Recreational activities such as rock climbing or canoeing are not considered to be sports by some people. Nevertheless, they can be used to meet the three-day moderate to vigorous recommendation for active sports if performed vigorously. Recreational

Figure 1

activities such as fishing and chess are not considered to be in this category. These activities have benefits, but are not in the moderate to vigorous physical activity category.

Flexibility exercises are included at Level 3 of the pyramid. These are referred to as exercises because they are done specifically to build the part of physical fitness called flexibility. Flexibility is the ability to use joints through a full range of motion as a result of having long muscles and elastic connective tissues. There are, no doubt, some activities from the first two levels of the pyramid that help build flexibility to some extent. Still, to develop this part of fitness, it is necessary to do special flexibility exercises that involve stretching the muscles and using the joints through their full range of normal motion. For this purpose stretching exercises are best.

Flexibility exercises should be done at least three days a week, and as often as every day. The intensity requires stretching beyond normal to a point of mild discomfort. Each exercise is performed several times for 15 to 30 seconds. It is important to perform exercises for each of the body's major muscle groups.

Muscle fitness includes strength and muscular endurance. Exercises to develop muscle fitness are included at Level 3 of the pyramid. Some of the activities from the first two levels of the pyramid can contribute to the development of muscle fitness. But most experts agree that if you want to improve muscle fitness you need to do some exercises especially designed to build it.

The ACSM recommends that muscle fitness exercises be done at least twice a week. Exercises for several different muscle groups (between 8 and 10) should be done using a percentage of the maximum weight a person can lift. The percentage (intensity) depends on the type of muscle fitness to be developed. Each exercise should be performed 8 to 12 times (a set). More frequent training and additional sets or combinations of sets and repetitions produce larger strength gains, but the additional improvement is relatively small.

At the top of the pyramid is inactivity (Level4). Some inactivity is not necessarily bad. For example, we need adequate amounts of sleep, and after vigorous exercise rest is important. Also, there are benefits associated with activities that are fairly sedentary. Fishing can be a relaxing experience that helps people get away from the stress of daily living. Nevertheless, the Physical Activity Pyramid is meant to provide information about the benefits of regular physical activity. Sedentary living as a lifestyle is discouraged. Long periods of inactivity during the hours of the day when you are awake should be limited. People who only sit and watch television or who spend all of their free time playing video games are not getting the activity they need for good health.

Ideally, a person should do some regular physical activity from each of the first three levels of the pyramid each week. However, if doing activity at all three levels proves discouraging or seems to be too difficult, it is better to select activities from fewer categories, beginning with the bottom of the pyramid.

GENETICS, MATURATION, AGE, AND OTHER DETERMINANTS OF ACTIVITY

Studies have shown that some animals tend to be more active than others. Humans are no exception in that a genetic predisposition to be active is one of several factors that determine the daily activity levels of children and adults. While social and environmental factors account for more of the variability in human activity than genetics, there are several ways in which heredity is important.

Physical fitness is highly influenced by heredity, especially in childhood. The amount of variability in physical fitness associated with heredity ranges from 10 percent to as high as 60 percent (e.g., maximal aerobic power, 25%; muscular endurance, 21%; muscle strength, 30%; body fat, 25%; bone density, 30—60%). Evidence suggests that fit people are more likely to be active than unfit people, thus heredity influences activity levels via its relationship to fitness.

Recent evidence also indicates that all people do not respond similarly to regular physical activity. Large variations have been noted between people who have a hereditary predisposition to respond to physical activity and those who do not have this predisposition. In other words, some people have the genetic makeup to respond more favorably to physical activity than others. Given the same activity program, some show considerably greater improvements in fitness than others.

Maturation also influences physical activity and fitness. During puberty, the potential for physical activity to produce gains in fitness is enhanced. Thus, teens are more responsive to physical activity than children. The feedback from performance improvements stimulates an interest in activity among those who are more mature physically compared to those who are less mature and do not see similar benefits for the same amounts of activity. Those who mature early may be more inclined to see the benefits of regular physical activity than those who mature later.

There is an abundance of evidence to indicate that children are the most active group in society. Beginning in the early school years, activity drops consistently throughout life. The most precipitous declines occur during the teenage years. The drop in activity continues throughout life, though the drop from the teens to the early twenties is less dramatic than the drop-off from childhood to the teen years. Older adults (above 50) are typically less active than younger adults. Much of the decline with age can be attributed to decreases in dopamine levels, which are associated with decreases in motivation to be active, though social factors (influence of friends, family, and role models), psychological factors (self-efficacy, enjoyment, beliefs about activity, and barriers to activity), physical factors (weather, safety, convenience, and availability), and demographic factors (sex, education, and vocation) all play a role in adult physical activity patterns.

GUIDELINES AND APPROACHES TO INCREASING ACTIVITY LEVELS

Among the most important physical activity guidelines are those of the ACSM and the CDC, which has established guidelines for the promotion of physical activity among youth. In addition, Healthy People 2010 (2000), a statement of national health goals, includes important national health objectives relating to physical activity and outlines priorities for changing activity patterns of Americans. Important strategies include increasing moderate and vigorous activity, as well as involvement in activities for muscle fitness and flexibility through increased school physical education, decreased television viewing, improved facilities for physical activity, and increased programs to promote walking and cycling as daily life activities. Expanded worksite health-promotion programs, improved health and wellness education, and greater public information access are other strategies that are outlined.

It is important to point out that the physical activity guidelines that are appropriate for adults are not appropriate for children. Appropriate guidelines for physical activity for children, including applications of the physical activity pyramid for younger age groups are available in Physical Activity for Children: A Statement of Guidelines (1998) published by the National Association for Physical Education and Sports.

Charles B. Corbin

Robert P. Pangrazi

(see also: Behavior, Health-Related; Centers for Disease Control and Prevention; Chronic Illness; Coronary Artery Disease; Epidemiologic Transition; Foods and Diets; Healthy People 2010; Lifestyle; Nutrition )

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