 Our first objective is to characterize performance, as related to socket fit, of a vacuum suspension system using objective and subjective measures. We will do this by conducting a within-subject experiment to measure pistoning in three dimensions while walking, overall and regional changes in limb volume before and after a thirty-minute treadmill walk, mobility step counts and the perception of socket fit questionnaire as a function of prosthetic prescription vacuum suspension system vs. total surface bearing suction socket. 