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.
Your core strength depends in large part on your legs and lower back for support. This exercise works that entire complex by having you pin a stability ball under your hips as you bring your upper body up and back off the ball in a powerful motion. Don't arch—lift.
Lie face down on a stability ball with your chest on the ball and your feet on the floor behind you, with your weight on your toes. Bend your knees so that you are squatting behind the ball even as you are lying on it with your chest. Your hips should be level with your shoulders, and your thighs in a vertical line. Put your hands behind your head with your elbows out to the side. Note: If you find need more stability to do this exercise, place the soles of your feet against a wall. (see Photo 1).
- From the starting position, dig your toes into the floor for stability as you lift your shoulders up and forward off the ball. As your chest rises, press your hips into the ball, pinning it in place, until your chest and shoulders are upright even as your lower body is holding the ball in a very low squat (see Photos 2 and 3).
- Lower your body back to the starting position, until the ball is once again under your chest. Repeat the extensions for a set of 14, being careful not to let the ball roll away at any time (see Photos 4 and 5).