There is broad public awareness that regular physical activity can reduce the risk of developing many of the major health disorders of modern life, including heart disease and diabetes, and serve as an effective treatment for those with such diseases. Despite this knowledge, only about 45% of the adult U.S. population participates in some physical activity, with perhaps 22% exercising 3 times or more per week at a duration and intensity sufficient to increase cardiovascular capacity. Furthermore, on average, 1 of 2 individuals who begin an exercise program quit within the first 6 to 8 weeks. While these figures make it clear that most Americans would benefit from more physical activity, it has also been recognized that a small minority exercise excessively. Moreover, these individuals ...