Physical Activity and Health

Prior to 1900, virtually every aspect of life, including transportation, work, food preparation, and caring for one's property required physical exertion or movement. However, beginning with the Industrial Revolution, an immense number of inventions have provided convenience and relief from physical effort. This has created an environment in which people can be almost completely sedentary on any given day. This changed environment has unintended consequences as we are now beginning to fully understand the negative impact a sedentary lifestyle can have on health.

The benefits of physical activity (PA) have been extolled throughout Western history, but it was not until the latter half of the 20th century that scientific evidence supporting these beliefs began to accumulate. A significant amount of this evidence has come from prospective epidemiology studies involving large numbers of people followed for several years in which the relationship between PA and various health outcomes have been documented.

This entry summarizes the evidence from such studies to provide an understanding of the association between PA and different health benefits and risks. Where sufficient evidence exists, answers to the question, ‘How much physical activity is enough?’ are provided. However, since the vast majority of the epidemiology studies have involved participants above 18 years of age, only evidence on adults is considered. Research with adults shows that regular PA independently confers significant health benefits as indicated by marked reductions in the risk of developing several chronic diseases that are today's leading causes of death and disability. In some cases, the optimal dose of PA is unclear. However, current data suggest that at least 30 min/day of moderate intensity PA is very beneficial and, in some cases, more is better. The resultant health benefits are available to all persons across the adult life span and, therefore, a lifetime of PA should be a priority.