You’ve made the transition from the most common of crunches on the floor up onto the stability ball where you can achieve a greater range of motion, but short of doing 200 reps, how do you add more of a challenge from there? Simple: set yourself up in front of the cable trainer with the rope attachment. Sit on the edge of the ball and lean all the way back until you can grab each end of the rope in either hand (it helps to have someone hand them to you). Keeping your elbows bent and your hands next to your ears use your abdominal muscles to sit up straight. Slowly return to the starting position. Repeat for 10-15 reps.