9. Cut your workouts in half.
Introducing short bouts of vigorous activity can speed up weight loss and cut your workout time by up to half or more. Australian researchers found that women who alternated just 8 seconds of high-intensity exercise with 12 seconds of low-intensity activity for 20 minutes, 3 times a week, slimmed down faster than steady-paced exercisers who worked out twice as long. Those who did intervals lost up to 16 pounds, shrunk their bellies by 12% and their thighs by 15%, and gained, on average, 1½ pounds of metabolism-revving muscle in 4 months—without dieting! Get started with these 20-minute interval workouts.