Lie face-up and place your lower legs on a Swiss ball. Extend your right arm overhead and bend your left arm at a 90-degree angle; then grasp the upper portion of your right arm so you form a cradle for your head. Flexing your toes and holding the ball in place by contracting your hamstrings, crunch forward to the finish position. In this position, increase the tension on your abs by attempting to pull the ball towards you with your hamstrings. Return to the start and exhale. Your rectus abdominus can flex only about 30 degrees (strictly), so when you perform this exercise it may not be necessary to lift your shoulders off the floor to achieve peak contraction. You can make the exercise more difficult by pulling harder with your hamstrings, maintaining peak contraction longer and by holding a weight in your free hand.
To do it: Lie on the floor with your arms extended above your head and both legs lifted in the air at about a 45-degree angle. Inhale, roll your head and shoulders off the mat, press your ribs down toward your hip bones and exhale, lifting your entire upper body off the mat (keeping both legs up). At the top of the exercise, "land" your arms so that the arms and legs are parallel to one another. Then, breathe "naturally" while holding the top/up position for two slow counts. Reverse the action by inhaling and then rolling your back, shoulders and head down onto the mat exhaling at the start position.