Sit-ups on Ball
Sit towards the front slope of the ball. Place hands across chest, and lean back until parallel with floor. Lift up approximately to a 45 degree angle. Slowly lower back down to start position. Repeat until fatigued.
Extensions on Ball
Start stomach down (prone) on ball. Put your hands behind head or along your sides (easier). Slowly lift head, shoulders, chest to a 45 degree angle, and hold for moment. Then slowly lift back to start position. You can put your feet against the wall (as shown) for help. Repeat until fatigued.