Exercise Ball Crunch
Sit on top of an exercise ball with your feet placed firmly on the floor. Roll the bottom half of your glutes off the ball by sliding forward. Your lower back should be centered on top of the ball. Place your hands on the sides of your head,but don't use your hands to pull. Crunch your upper body forward and roll your shoulders towards your hips. Squeeze at the top. Then lower back to the starting position and repeat. You can hold a weight to increase the difficulty.