Xtest Muscle Wall sits are fast and simple ways on which you can build leg strength. Make sure you find a big enough wall space for you to do wall sits on. Stand with the wall behind you about 18 inches. Crouch down slightly at the knees then slowly lean backwards so your back is resting against the wall. Keep bending your knees to the point that your thighs appear parallel with the ground in a sitting position. Remain in place for as long as you can tolerate it.
http://www.healthbuzzer.com/xtest-muscle/