Like distance runners on measured course, all of us will move through time in a roughly predictable pattern. In the first stage of our lives, we develop and grow, reaching toward the top of physical vitality (energy). After we grow up, however, the body begins a process of gradually wearing out. A new awareness of physical fitness may help lengthen our years of health and vitality, yet nothing we do will work to stop the unavoidable force of aging. Most of the changes of aging take place deep inside the body. The lungs become less able to take in oxygen. Powerful muscles gradually l