Stability ball abs... I love the stability ball, it's a great tool to use because it adds the need to balance, which works the big muscles and the intrinsic muscles (muscles that support your big muscles) to give you an all around workout. Start out by going into a pushup position with your hands on the ball and your feet on the ground. Hold for 30 seconds. Once you master this move, you can start pulling a knee up to the ball and balance, and then place your foot back on the ground.