Book excerpt: Aging, despite its dismal reputation, is actually one of the great mysteries of the universe. Why don't we just reproduce, then exit fast, like salmon? Could aging just be one big evolutionary accident? Is senescence, the gradual falling apart of our bodies, at least partially avoidable? Can we extend the healthy lifespan and reduce the lingering, debilitating effects of senescence? In this book, investigative health journalist Judy Foreman suggests that we actually can, and the key element is exercise, through its myriad effects on dozens of molecules in the brain, the muscles, and other organs. It's no secret, of course, that exercise is good for you and that exercise can extend longevity. What Foreman uncovers through extensive research into evolutionary biology, exercise physiology, and the new field of geroscience is exactly why exercise is so powerful - the mechanisms now being discovered that account for the vast and varied effects of exercise all over the body. Though Foreman also delves into pills designed to combat aging and so-called exercise "mimetics," or pills that purport to produce the effects of exercise without the sweat, her resounding conclusion is that exercise itself is by far the most effective, and safest, strategy for promoting a long, healthy life. In addition to providing a fascinating look at the science of exercise's effects on the body, Foreman also provides answers to the most commonly asked practical questions about exercise.