This version of the leg curl is one of the most demanding hamstring exercises you will find. One should at least have an intermediate level of workout experience before attempting this exercise. A certain degree of muscle control is required in order to be able to stabilize the ball. But with a bit of practice, anyone can master this exercise. It is important to thoroughly warm up your hamstrings before performing this exercise, as the starting resistance level is high.

Start on your back with your heels/ankles on top of the stability ball. Place your hands by your sides, palms face down. Next, lift your hips off the ground. As the hips come up, use your leg muscles to roll the ball in toward the butt. Your knees should bend to at least 90 degrees or more. In the fully bent position, your shoe soles should be firmly on the ball. Finally, slowly return to the starting position and repeat the movement.