If you've mastered how to do abdominal crunches on the floor, you might be looking for a new way to condition the muscles in the middle of your body. This exercise uses a ball to accomplish that. As a beginner, try to concentrate on using a small range of motion. With practice, you can gradually make the motion larger.
1 Start in a push-up position, with your shins and ankles on top of a large stability ball. Make sure your hands are directly below your shoulders, with your fingers pointed forward and elbows straight.
2 On an exhale contract your abdominals and round your lower back as you pull your knees toward your chest. When your legs are about halfway in, pause for a moment and focus your attention on working your midsection by pressing your navel to the spine. For a more advanced movement, you can continue to roll the ball a little further in toward your chest.
To return to the start position, reverse the movement and slowly roll the ball away from your chest as you straighten your legs. Use your abdominals to keep your entire back straight and don't let it sag in the center. Repeat eight to 12 times, rest for 30 seconds and do a second set.