By the early to mind-1980s,it had become clear that physical inactivity was a major public health concern (30). In 1992, the American Heart Association made physical inactivity a major risk factor for cardiovascular diseases, just like smoking, high blood pressure, and high serum cholesterol (3). In 1995, the Centers for Disease Control and Prevention (CDC) and the American College of Sports Medicine published a public health physical activity recommendation that "Every U.S. adult should accumulate 30 minutes or more of moderate-intensity physical activity on most, preferably all, days of the week" (28). A year later, the Surgeon General's Report on Physical Activity and Health was published (36).