Evidence for the health benefits of physical activity is overwhelming: physical activity is protective against type II diabetes, cardiovascular disease, breast and colon cancer, stroke, osteoporosis, depression, falls in older adults, and many other adverse health outcomes. Research also suggests that widespread physical inactivity exacts a heavy toll on the US economy, as well as on individual health. Researchers have estimated that those who are physically inactive impose greater costs on society than do smokers or problem drinkers. . . .