Many individuals are living in the United States with limb loss. With the use of a prosthetic device many individuals can stay active, but most do not achieve a medically desired physical activity level. This creates a risk for cardiovascular disease. It is thought that individuals with amputation walk less because it is more difficult to get around, and recent advances in robotic prosthetic technology may make such activities easier. However, these prostheses have not yet been evaluated to determine their effectiveness during extended periods of walking. Despite the goals in design of new devices it is unclear whether individuals using them are able to incorporate them into making daily activities easier. Therefore, the goal of this research is to determine the effectiveness of a powered prosthesis compared to an unpowered prosthesis during long periods of walking.