A complete guide to a technique long used in athletic training--carefully explained here for those who run, swim, cycle, or do any other kind of regular exercise. Building on the program they developed at Ohio State, the authors describe interval training (IT) as short periods of activity alternating with longer periods of rest--less painful and seemingly more fitness-producing than continuous exertion. Aside from the usual benefits of any exercise (improved physical shape, weight control, cardiovascular fitness), IT has the bonus of being less boring; the program is designed so that different activities (running, swimming, even calisthenics) are interchangeable from day to day, with exercise periods planned for three times a week. Explaining the differences between aerobic and non-aerobic exercise, the authors note that the program can be adjusted to emphasize one or the other: exercise requiring bursts of energy (squash, sprinting) has a large anaerobic component and hence practice is planned differently from that which is aerobic (e.g., distance running). There are detailed, eight-week practice plans for a variety of sports (from running to bench-stepping); for serious trainees, the authors explain how to tailor-make an individual program. The only mundane and relatively uninformed advice here is on nutrition: selections from the traditional basic food groups are recommended, while a high calorie diet for those in training lists, for lunch, five fish sticks with tartar sauce and one large serving of french fries. Otherwise, a sound presentation of one of the most interesting and varied ways of exercising.