Trying to get rid of a stubborn tummy pooch? Interval training is proven to blast belly fat. Here's a 45-minute interval workout you can do on the treadmill (set the incline to one to prevent shin splints) or head outdoors and use one of these running apps on your iPhone to keep track of your speed. Or you can use the RPE column on the right to determine how fast you should be going. You'll end up burning 303 calories while toning your tush and thighs. If this workout is a cinch or way too difficult, then adjust the speed to fit your level.