Set-up: Position a stability ball by your feet and your upper back on a mat.
Lift: Place your heels on the stability ball. Lift your hips off the floor so that a straight line forms between your shoulders, hips and heels. Keeping the hips elevated and the core tight, bring the heels toward your body, rolling the ball towards your rear end.
Repetitions: Perform all prescribed reps on one side, then on the other. This counts as one set.
Training Impact
Muscle Roles in stability ball hamstring curl - single leg
Instructions and effects for the Stability Ball Hamstring Curl - Single Leg exercise 
