The eleventh in a series by Scot Willingham.

@##=#<1,R>@##=#10 Inverted Reverse Crunch on ball

Muscles worked
Primary: Abdominals (all of them)
Secondary: Pectoralis major, Serratus Anterior, Deltoids, Trapezius, Rhomboids, erector spinae
Tertiary: Muscles of the arms
Equipment: Swiss ball

Safety tip: If you have lower back problems or have a tendency to strain your lower back, skip this exercise.

Put down that band/tubing and get that Swiss ball again. Start on your hands and knees on your mat with the ball at your feet. Supporting your weight with your hands, first put one shin on the ball, then the other shin. You should be in an altered push up position with your legs straight and the weight on the shins resting on top of the ball. Your hips should be slightly higher than your shoulders to protect the lower back.Take a moment to find your balance as just maintaining this position can be an excellent ab exercise.
Once you find your balance, draw up and in with your abs, bending at the hips, rolling the ball toward you and slightly bending your knees up toward your chest. Your butt and lower back should go up toward the ceiling and your belly button should feel as if it were being sucked up into your back. Then slowly return to your starting position. Do NOT stretch out to your full length, but keep your hips higher than your shoulders, and your abs actively pulled in to protect your lower back. Repeat until fatigue.

Simpler version: Rest your thighs on the ball and move in and out from that position.

Stud muffin version: Rest the tops of your feet on the ball and move in and out from that position.

To get out of this exercise:
walk your hands back towards the ball until it is supporting your chest. You will be draped over the ball because you are a little tired. Stay there and rest. It is a great lower back stretch.