Declining rates of physical activity in the United States: what are the contributors?

This review describes current patterns and long-term trends (up to 50 years when possible) related to (a) physical activity, (b) employment and occupation, (c) travel behavior, (d) land use, and (e) related behaviors (e.g., television watching). On the basis of available data, the following trends were observed according to type of physical activity: relatively stable or slightly increasing levels of leisure-time physical activity, declining work-related activity, declining transportation activity, declining activity in the home, and increasing sedentary activity. These result in an overall trend of declining total physical activity. Large differences were noted in the rates of walking for transportation across metropolitan statistical areas. A strong linear increase existed in vehicle miles traveled per person over the past half century, coupled with a strong and consistent trend toward Americans living in suburbs. Although it is difficult to precisely quantify owing to the lack of long-term data, it is apparent that a combination of changes to the built environment and increases in the proportion of the population engaging in sedentary activities put the majority of the American population at high risk of physical inactivity.