Leg Curl on Swiss Ball

Lie on the floor with your calves on a stability ball and your arms at your sides. Squeeze your glutes to raise your hips off of the floor so your body is in a straight line from your shoulders to your ankles. Pause for a second, then bend your legs to roll the ball toward your butt. Straighten your legs to roll the ball back out away from you, then lower your body to the floor.