Science writer Jörg Blech sets out the actual physiological effects of exercise: it triggers the growth of new brain cells, induces stem cells in blood vessels, and reverses symptoms of heart disease and type 2 diabetes. Doctors are now using exercise to combat common ailments such as heart disease, arthritis, diabetes, osteoporosis, and depression. Everyone--whether a healthy athlete, a patient seeking to overcome a chronic disease, or a person...