Whether on the treadmill or outside in nature, interval-style running is a real fat burner. It's a super effective exercise that involves running at full throttle for a specified time interval (usually up to 60 seconds), followed by walking or jogging for another specified time interval (shorter, the same or longer than the sprint interval). A good ratio to start out with is 30/60: 30 seconds of sprinting, 60 seconds of walking/jogging. And in terms of calorie expenditure, a 180-lb person doing sprint intervals at 12 mph for 20 minutes can burn about 608 calories + the calories burned from EPOC.