S.F.
Sit in front of the yoga ball. Position the ball in front of you and lean your tummy on the ball with your torso hanging off the front of the ball a bit. Have your legs straight behind you. So... basically you're a plank sitting on a ball... like a teeter-totter. Put your hands on your hips with straight posture. Lift your torso up and back (like a reverse crunch). Repeat slowly. Hold position as you pull back briefly, then slowly release to the straight position.
This will build abs and back muscles. This is important because the two muscles support each other in any movement. Have a strong back and weak abs could still cause back strain.
If you don't have a yoga ball, you can also buy a huge plastic ball in the toy section at Wal-Mart or any kids store for about $5.00. It's not quite as sturdy, but it gets the job done. Plus, the kids can play with it in the meantime!
I can probably explain better on the phone if you're not quite sure what I'm saying.
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