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.

Benefits
Doing crunches on the stability ball allows you to stretch all the way back on the crunch descent, working your abs with a wider range of motion than you can get with a floor crunch.

Muscles worked
Abdominals

Starting position
Sit on a stability ball with your feet on the floor in front of you 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. Place your hands behind your head in standard crunch position, with your elbows back and relaxed (see Photo 1).

Exercise

1. From the starting position, engage your core muscles and roll your upper body up until your shoulder blades are off stability ball and your upper body just breaks the plane of being flat. Use your hands to gently support your head, but do not pull up with your arms (see Photo 2).
2. Reverse the motion and, with your core engaged, lower yourself back to starting position (see Photo 3).