How do I perform a ball crunch?

Lie on a stability ball with the ball placed under your low back, bend your hips slightly and keep your knees lined up directly over your ankles. Your feet should be placed flat on the floor, hip width apart. Extend your back over the curve of the ball and cross your arms over your chest. Draw-in your navel and contract your glutes. Crunch your upper body forward, being careful not to move your hips off the ball. Return to the starting position and repeat.

Position yourself with your feet flat on the floor and lie with your body on the stability ball, fingertips behind your ears and elbows back.  Add some variety to the crunch by holding a weighted plate or dumbbell across your chest while raising your head and shoulders off the ball and crunching your rib cage toward your pelvis.  Remember to keep your abdominals drawn in and your glutes contracted while you slowly return to the start position.

To Start:
1. Lie with ball under low back and knees directly over ankles; feet on floor, hip-width apart.
2. Extend back over curve of ball and cross hands on chest.

Now:
3. Draw-in belly button and squeeze butt muscles.
4. Crunch upper body forward.
5. Lower upper body.