The objective of the proposed research is to use photo-oximetry to discover which of five different prosthetic limb systems results in higher residual limb tissue oxygenation during both rest and gait. This experiment will enable evidence-based decision making on this clinically relevant problem. Using a prospective, randomized cross-over experimental design and the investigators' photo-oximetry system, the investigators will measure and compare the tissue oxygenation along the medial and lateral surfaces (3 sites each) of the residual limb during rest and walking.