3. Put on some weight.
To really rev your calorie burn, it is not about the number of reps, but the size of the weights. Even when exercisers lifted identical volumes (such as 10 pounds 10 times or 20 pounds 5 times), those using the heavier dumbbells burned about 25% more calories when they were finished. “Heavy weights create more protein breakdown in the muscle, so your body has to use more energy to repair and recover—that’s how lean muscle tissue is built,” says researcher Anthony Caterisano, PhD, of Furman University. Bonus: working out with heavy weights even for as few as 3 to 6 reps increased exercisers’ sleeping metabolic rate—the number of calories burned overnight—by nearly 8%. That’s enough to lose about 5 pounds in a year, even if you did nothing else! (Give this super-speedy sculpting routine a try.)