The benefits of physical activity (see below) are well-established, and emerging studies continue to support an important role for habitual exercise in maintaining overall health and well-being. Persuasive epidemiological and laboratory evidence shows that regular exercise protects against the development and progression of many chronic diseases and is an important component of a healthy lifestyle. Recent studies correlating changes in physical activity in initially sedentary adults with subsequent reductions in mortality have supported the hypotheses that regular activity increases longevity. The public health benefits of increasing physical activity with the general population are potentially enormous due to both the prevalence of sedentary lifestyles and the impact of activity on disease risk. Furthermore, data in recent years suggest that the threshold necessary for the health benefits of exercise, such as significantly lowering chronic disease risk, is lower than previously thought. There is a clear inverse relationship between activity and mortality risk across activity categories, and the risk profile indicates that some exercise is better than none, and more exercise--up to a point--is better than less. Thus, public health efforts should be directed toward getting more people more active more of the time rather than elevating everyone to an arbitrary fitness or activity level.