Your hamstrings consist of a group of three leg muscles that, when injured, are slow to recover. Building hamstring strength may help you avoid injury as well as improve your overall lower body performance. Stability balls offer a variety of hamstring exercises that strengthen these leg muscles. In addition, the dynamic nature of stability balls promotes body balance by recruiting stabilizer muscles as you perform the exercises, according to the American College of Sports Medicine.

Leg Lift

The leg lift on a stability ball targets primarily your hamstring muscles and, to a lesser extent, your back muscles. With the stability ball on a stable surface, roll your body forward until your hips are centered on the ball. Support your upper body by placing your hands on the floor directly beneath your shoulders. Extend your legs behind you so that your body is in a straight line from head to heels. Without arching your back or bending your knee, lift your left leg toward the ceiling as high as possible. Hold for a count of five, and then lower your left leg and raise your right leg. When you can easily perform 20 reps with each leg, intensify the exercise by raising your opposite arm parallel to the floor as you lift your leg.

Hamstring Curl

The stability ball hamstring curl focuses intently on your hamstrings, with a smaller emphasis on your gluteus muscles. Lie on your back with your calves atop the stability ball. Contract your abs and press your hips upward to form a straight line between your chest and your feet. Slowly bend your knees as your feet roll the ball inward toward your glutes. Continue to raise your hips until the soles of your feet are on top of the ball and your chest is aligned with your knees. Hold this position for a moment before rolling back to your starting point with a controlled motion. Repeat 10 times. The American Council on Exercise recommends increasing the challenge to your hamstrings by raising your left leg up to the sky and performing the curl with your right leg only, then switching sides.

Stability Ball Lunge

The stability ball lunge using a fitness ball not only can improve your hamstring strength, but also increases the strength of your core, glutes and quads. Reinforcing all these muscles helps protect your hamstrings from injury. Position your left ankle on the stability ball behind you, right foot supporting your weight as you slowly bend your right knee until your thigh is parallel to the floor. At the same time, roll the ball in from your ankle to your shin, keeping your torso upright and your left leg straight behind you. Hold for several seconds and then return to starting position. If necessary, hold on to a wall until you are able to balance yourself through the movement. Perform 10 repetitions, then repeat with your other leg.