We've all heard the mantra, exercise for good health. In fact, exercise, or lack of it, may be the most important factor in avoiding, or surviving and recovering from, the top three killers across developed countries-heart disease, cancer, and stroke. But few of us understand exactly how different forms of exercise work-physiologically speaking-to keep us healthy and prevent or treat disease. Here, two nationally known exercise experts lead a stellar team explaining, in reader-friendly terms, what exercise does to our bodies and how it spurs beneficial biological actions.

Julie K. Silver, M.D., is Assistant Professor at Harvard Medical School and Medical Director of the International Rehabilitation Center for Polio. She is a board-certified physiatrist and a graduate of the Georgetown University School of Medicine. She is also Series Editor for two Praeger series, The Praeger Series on Contemporary Health and Living, and The Praeger Series on Healing and Managing Injury and Disease.

Christopher Morin is Founder of the American Fitness Testing Association and owner of a personal training center in Southborough, Massachusetts. He is a former bodybuilder who won 10 titles including Mr. Eastern USA, New England Bodybuilding Champion, and Natural Atlantic Coast Champion. The holder of a master's degree in health and fitness education, Morin has been trainer, nutritionist, and coach to amateur and professional athletes including 40 regional bodybuilding champions, two national champions, and one three-time world champion.