To do a crunch on an 8” inflatable ball with added rotation, begin by lying down on your back. Place the ball between your legs. Lift your legs so that they are bent at the knees. Your lower legs should be parallel to the ground. Cross your arms over your chest. Lift your shoulders and your upper back off the ground to do a crunch but, as you lift your body, rotate to the right and then recline to the starting position. Now repeat the movement on the opposite side.
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