Anytime your hands go above your head, your abs are forced to work. Add a dumbbell to the move, and they work harder. Stand with your feet slightly wider than hip-width apart and toes pointed slightly outward. Holding one heavier dumbbell with both hands. Sit back into your squat bending your knees to 90 degrees while keeping your elbows straight, and raise the weight overhead. Lower your arms as you straighten your knees to stand; this completes one rep. Do 15 reps for a set.