Instructions
Lie with your back on the floor and place a swiss ball between your lower legs. Squeeze your legs into the ball to ensure a tight grip. Raise your legs so that they form a 90 degree angle with your body. Keeping your legs straight, and your arms on the floor by your sides, contract your abdominals and crunch your lower abdominals up until your buttocks raise slightly off the floor. Lower your buttocks back to the floor then slowly lower your legs towards the floor. Only go as low as you can maintain the natural curve in your back. Raise your legs back to the starting position to repeat the whole exercise.
Tips
Do not use momentum/swinging to raise your buttocks off the floor in the reverse crunch movement. If you are not able to raise your buttocks, you will still work your abdominals if you focus on contracting the muscles.