High-Intensity Interval Training is a new workout trend that involves short, intense bursts of exercise, followed by periods of lower-intensity exercise or rest. In turn, the body burns more calories in a shorter period of time than traditional exercise routines. Idiot's Guides: High-Intensity Interval Training is a full-color, step-by-step guide that is packed with over 80 exercises, structured routines, and intense programs that can be done anywhere, anytime.