Exercise · Hips

Clamshell

Lying on your side with your knees bent and stacked, you open the top knee like a clam while your feet stay together. It is a small, isolated way to make the gluteus medius — the muscle on the side of the hip that keeps the pelvis level when you stand on one leg — work without the leg's full weight to lift. Momentum's system lists glute med as commonly weak, names weak glutes as a cause of knee pain, and blames knee collapsing inward on poor hip control. This is the first rung of the activate-glutes step in the running flow.