This exercise provided courtesy of Billy Polson, founder and co-owner of DIAKADI Body training gym, voted best personal training gym in San Francisco by CitySearch in 2006.
Doing abdominal work on the stability ball is great because it allows your abs to flex and move within the full range of motion. The unstable surface of the stability ball also increases the difficulty of situps because it forces you to continually balance and re-balance throughout the movement. The addition of the medicine ball to the stability ball situp ups the ante further by adding additional weight that your abs need to lift.
Lie back on a stability ball with your feet on the floor in front of you about hip-width apart and a medicine ball held in your hands, arms extended overhead with biceps beside your ears. Your body should supported between the top of your buttocks and the bottom your shoulder blades and your head and shoulders should be hanging off the other side of the ball. Try to stretch back over the top of the stability ball while keeping your abs engaged (see Photo 1).
- From the starting position, fully engage your abdominal muscles and lift your upper body and the medicine ball up. Lift until your entire upper body is off the stability ball and vertical and you are holding the medicine ball out in front of your face. Keep your abs engaged throughout the lift, even when you are at the top of the movement (see Photos 2 and 3).
- Reverse the motion and, with your abs still engaged, lower yourself back to starting position (see Photo 4). Do 20 repetitions for a full set.