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.
The stability ball, now common in most gyms, started out as a physical therapy tool. Soon trainers began to use them as an unstable surface to do abdominal work as well as a supportive device to allow clients to strengthen their abdominals through a range of motion. These center and oblique situps are staples of those abs workouts, providing excellent muscle isolation that will help you develop those hard-to-train muscles.
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, the upper half of your abdominals are resting right at the peak 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).
- From the starting position, engage your core muscles and crunch 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).
- Reverse the motion and, with your core engaged, lower yourself back to starting position. Do 20 repetitions of the center situps before switching to your obliques.
- To do oblique situps, begin at the starting position for center situps, then turn your entire body to the right so that your right hip and right side are resting on the stability ball (see Photo 3). Again, set up high on the ball so that the center of your obliques are at the peak of the ball, allowing your upper body to lay down across the other side.
- From the oblique starting position, use your left oblique muscles to crunch your body up until your body comes just past a flat position (see Photo 4).
- At the top of the crunch, reverse the motion and, with your left obliques engaged, lower yourself back to starting position. Do 20 repetitions on your right side before turning over and doing 20 repetitions on your left side.