STABILITY BALL CURL Target Muscles: hamstrings Synergist Muscles: gastrocnemius, erector spinae Set Up: Lie supine on the ground with your legs straight and your heels on the top of an exercise ball. Lift your hips up as high as you can [A]. Action: Roll the ball toward your body by bending your knees. Hold for a second [B] and then extend your legs. Repeat for three sets of 15 reps.