Grab a five-to 10-pound medicine ball (or dumbbell). Lying faceup on a stability ball with your upper back and head pressed against the ball and your feet together on the floor, hold the medicine ball against your chest. Brace your abs and crunch up until your shoulders are off the ball. Then reach the ball toward the ceiling. Lower it and return to the starting position. Do 12 to 15 reps. Tip: Control your movement through the entire exercise, bracing your core and keeping your back flat.
