Physical Activity Health Article

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.