Can Vibration Stimulation of the Foot Sole Activate Leg Muscles?

Participants will be asked to complete three different tests (standing, stepping and assisted walking) and will experience three different experimental conditions during each test. The three conditions are types of vibratory plantar cutaneous stimulation, which include no vibratory stimulation, submaximal vibratory stimulation and supramaximal vibratory stimulation. In the first condition, participants will experience no stimulation applied to any part of the body. In the second condition, a submaximal vibratory stimulus will be delivered at 90% of the participant's threshold to the surface of the foot. In the third condition, a supramaximal vibratory stimulus will be delivered at three times the participant's threshold. The hypothesis is that this plantar stimulation (90% threshold and supramaximal) will elicit increased muscle activity during these tests. If the hypothesis is positive then this protocol will also be presented in incomplete spinal cord injuried participants.