Stability Ball Leg Curl

The stability ball leg curl trains the hamstrings in both of their jobs at the same time. Lying on your back with a heel on the ball and the hips lifted, the hamstring has to extend the hip to hold the bridge and flex the knee to roll the ball in, which is a combination no machine reproduces. Performing it on one leg doubles the load on the working side without any equipment at all, and immediately reveals the strength difference between legs that a two-legged version hides. The part most people find surprising is the return. Rolling the ball back out while keeping the hips high is an eccentric contraction under a long lever, and it is where cramping usually appears. Keep the hips level with the shoulders throughout; the moment the pelvis drops, the hamstring has stopped working.