Step strengthening exercise. Stand on a step and tighten the quadriceps as you bend and straighten the knee. Particularly try to tighten the inside muscle (vastus medialis), as usually this is the weakest of the quadriceps. Use the other leg as a lever by extending it down over the step. strengthening of this muscle, combined with stretching the hip abductors (exercise66) and strengthening the outer hip muscle (exercise68) can assist if you suffer from 'runner' s knee' (pain under the kneecap)