ABSolutely the Best

Crunching Success
In a recent survey reported by Reps Magazine, 500 fitness instructors chose crunches on the exercise or swiss ball as the best abdominal exercise. The consensus was that the exercise ball injected a more intense workout and greater range of motion than the conventional standard crunch.
How to cruch on a ball:
Position the ball to support the back, keeping the feet flat on the floor.
With slow movement, curl up and forward.
Hold for a second or two
Return to start position
For more intensity hold your hands over your head or behind the neck. (If you choose behind the neck do not use your hands and arms to pull you up, just positin them behind the head. Pulling with your hands can cause injury.
Maximum Intensity: do the movement while holding additional weight in your hands above your head or behind the neck. (Once again do not pull with the hands for safety)