Lying on your back with your knees bent and your feet against a wall, hold a three- to five-pound medicine ball over your head with both hands. Do a basic sit up, and while in the upright position, throw the ball against the wall and catch it on the rebound. Slowly lower to starting position. For extra credit, hold the medicine ball above your head and hinge sideways at your waist while you sit up. Keep your lower back straight, drop the ball down to the ground beside you, and catch it. Repeat for three sets of 20 reps.