 Both the control and study group will have gait analysis measurements performed as a baseline for data collection. After a six minute acclimatization period at 4kmh on the instrumented treadmill Kistler Gaitway, Kistler Instrument Corporation, Amherst, NY, the speed is increased until either the subject feels uncomfortable, or the walking performance deteriorates. The procedure generally takes 12 minutes of continuous walking. Following the flat ground assessment, the inclination is then increased in 5 increments at a steady 4 kmh, until either the subject feels uncomfortable, or the walking deteriorates. The treadmill is then ramped to an inclination of 7 downhill. The subject is then asked to walk initially at the same 4 kmh, and then at 0.5 kmh increments until they either feel uncomfortable, or the walking performance deteriorates. 