Calculate your max heart rate by subtracting your age from 220, then use the built-in heart rate monitor on the treadmill or elliptical to track your ticker while you work out. Aim to do short bursts of high-intensity exercise at 80 to 85 percent of your max, followed by low-intensity recovery periods at 50 to 65 percent max. This method burns more calories than exercising at a consistent level of exertion for the same amount of time. Source: American Collage of Sports Medicine
