Place ball at low back area and place feet wide to stabilize the body. Cross arms over chest. In a controlled motion, keeping neck straight, curl upper body up. Contract abdominals fully without compromising form. While maintaining the controlled motion, return to starting position. Do not allow muscle to relax before next repetition.
Here are a few suggested alternative exercises:Ab CrunchAb Crunch ObliquesBall Crunch TraditionalDouble CrunchDumbbell Side BendsLateral Bend with Barbell