Amputees work harder and have greater oxygen cost during ambulation compared to those without limb loss. Therefore, amputees generally walk slower and tire more easily than intact individuals. The loss of the ankle as a propulsive and supportive joint requires the amputee to perform extra muscular work with the hip, trunk and contralateral limb during ambulation. This increased muscular activity consumes additional metabolic energy and means that amputees have to work harder to walk at the same speed as intact individuals. For some amputees, this extra effort is simply not possible, and their loss of functional ambulation leads to a progressive spiral of disuse, reduced capacity and more disuse. Conversely, greater mobility can lead to greater activity and even more successful return to the workplace. The health consequences for amputees who do not maintain functional ambulation is multifactorial and costly, not only in terms of dollars for the institutions committed to their care, but also for the individuals themselves in terms of decreased quality of life, increased disability and pain. Recent developments have resulted in the design of a novel prosthetic foot that uses the energy from compressive forces during heel contact, stores it throughout midstance and releases it at an optimal instant during push-off in late stance. This unique design, with Controlled Energy Storage and Release (CESR) developed by a team at the University of Michigan, Ann Arbor has been shown to reduce the metabolic cost penalty of prosthetic ambulation (i.e. the increased cost over normal walking) by 50% compared to a standard SACH foot, but as yet only intact individuals wearing an aircast boot equipped with the prosthetic feet have been studied. It is likely that the increased energy savings will also be observed in transtibial amputees. Young, active amputees will soon be entering the VA system following operations in Iraq and Afghanistan, and the energy improvements may benefit this new VA patient population. The CESR foot may also provide substantial metabolic cost savings to older less active amputees currently in the VA system. By improving gait efficiency amputees will be better able to keep up with the demands of functional ambulation, remain more active and postpone many of the debilitating consequences of limited mobility. Therefore we propose to first refine the design of the CESR foot focusing on the energy storage and energy release mechanisms of the CESR foot. Several spring characteristics may prove optimal for certain subjects depending upon weight and walking characteristics. This will be an iterative optimization process with power generation and absorption characteristics of the CESR foot evaluated using computerized gait analysis and the lessons used for further refinement. The second phase will involve a three week wear-testing trial to determine if any improvement in gait economy, reduction in fatigue, improvement in comfort, or increase in the amount of daily walking can be achieved. A validated questionnaire will be utilized to determine each amputee's comfort and fatigue during a three week trial in their conventional foot and with the CESR foot. Step counts will be performed on each individual over the entire 3 week period with both the conventional foot and with the CESR foot. We will collect full body gait kinematics (motion) and kinetics (forces) using our Vicon 612 system, and metabolic measurements using our VmaxST to calculate oxygen cost for 24 transtibial amputees while walking with the CESR foot and their conventional foot. This will permit the calculation of the energy storage and release of the foot by inverse dynamics and calculate the net effect upon metabolic energy cost savings during ambulation at several speeds. If the CESR foot is successful in amputee gait these domains, our next step will be to perform a multi-center study with other VA motion laboratories, and eventually collaborate with Ohio Willow Wood, a prominent prosthetic manufacturer who has expressed an interest in bringing the CESR foot to market.