Participants will be asked to perform movements such as walking, walking up or down stairs, standing quietly or reaching for an object. For the test, the arms and legs are wrapped with a soft, rubber-like material to which small plastic reflective balls are attached. A piece of firm material called a shell may be attached to the rubber sleeves or other areas of the body. Then the volunteer performs the specified task several times while special cameras record the movement. The cameras only record the positions of the reflective balls during movement, not the person s face or body. Electrical activity in the muscles also may be measured, using small metal electrodes attached to the surface of the skin with an adhesive bandage.