STABILITY BALL REVERSE CRUNCH

This crunch is similar to the previous exercise, because you initiate the movement from the lower body instead of the upper body.

1. Lie on the back and rest the lower legs on top of a stability ball so that the ball is tucked underneath the knees. Beginners keep the arms at the sides; advanced place them behind the head.
2. Dig the heels into the ball and contract the abs to bring the knees to the chest.
3. To make it harder, lift the butt off the ground and bring the knees to the chest at the same time, while the arms are behind the head.
4. For the most advanced reverse crunch, do an upper-abdominal crunch simultaneously with the lower-abdominal crunch.