Use a larger light “stability ball” that’s about 22″ diameter, or as shown here, for more of a challenge, a weighted exercise ball (we’re using an 8lb ball). Stand back-to-back, knees bent, and exchange handing off the ball twisting at the waist, for ab/core toning and flexion. The heavier the ball, the slower you should go. This is an effective and fun partner challenge segment. Click on photo to enlarge.