This exercise provided courtesy of Mike Clausen, founder and co-owner of DIAKADI Body training gym, voted best personal training gym in San Francisco by CitySearch in 2006.
Doing crunches on the stability ball works your abs with a wider range of motion than you can get with a floor crunch; adding a weight plate behind your head increases intensity across that wider range of motion.
Sit on a stability ball with your feet on the floor in front of you and approximately hip-width apart. Lie back on the stability ball so that your body is supported between the top of your buttocks and your shoulder blades, your abdominals are centered right at the top of the ball, and your head is hanging off the other side of the ball. Take a weight plate in both hands and place it behind your head with your head resting lightly on the plate and your elbows out to the side (see Photo 1).
- From the starting position, engage your core muscles and roll your upper body up until your shoulder blades are off the stability ball and your upper body just breaks the plane of being flat. Your head should still be resting lightly on the weight plate, but the plate should not be pulling your head up—use your arms to support the plate, but your abs to lift your upper body (see Photos 2 and 3).
- Reverse the motion and, with your core engaged, lower yourself back to starting position. Again, the weight plate should stay right behind your head (see Photo 4 and 5).