Unilateral trans-femoral amputee gait consumes up to 60% more energy than able-bodied gait. For higher level amputees, research suggests that energy efficiency drops by well over 80%. Recently it has been shown that energy consumption in high level amputees increases significantly when walking on slopes, suggesting studies in level walking may underestimate the extent of the problem. The negative effects of high energy consumption are compounded by reductions in walking speed of typically 40% for trans-femoral amputees with associated low activity levels, particularly in elderly amputees. These deficits are even greater in bilateral amputees. This has a tremendous impact on what amputees can achieve and the consequences for their quality of life.The energy storage and return capabilities of prostheses are crucial to improving the situation and yet modern prostheses only store and return significant energy below the knee, and energy is not returned in a controlled manner. For example, stored energy is not available for plantar-flexion (push-off) at the end of stance. Furthermore, modern prosthetic systems don't transfer energy between joints, which is a lost opportunity as, for example, the excess of eccentric work at the knee could be stored and used in a controlled manner at other joints. For these reasons, we believe there is an opportunity for truly transformative research leading to a step change in the performance of lower limb prostheses.We have been undertaking simulation studies to establish the potential for hydraulic technology to enable controlled storage, transfer between joints, and return of energy in lower limb prostheses. Although the work to date has focussed on prostheses for trans-tibial amputees, this approach has even greater potential for improving the energy efficiency of trans-femoral amputee gait. We are focussing on hydraulic designs because of their unique advantages for the prosthetics application. Because they typically operate at pressures of 200 to 400 bar, hydraulic systems have very high power densities and are therefore well suited to miniaturisation, an important requirement in prosthetics. Short term energy storage is another important requirement for which hydraulic accumulators are well suited. Finally, hydraulic actuation is ideally suited for transferring energy between joints because the transfer mechanism involves only pipes and fluid, rather than gears and linkages. This is of particular importance for higher level amputees who could benefit if the excess of eccentric work at the knee could be stored and used in a controlled manner at other joints.To achieve our objectives we have carried out research in three areas, which correspond to the three main work packages (WPs). WP1 has developed and simulated alternative concept designs. WP2 has established a methodology for predicting the ways in which amputees might adapt their gait to alternative prosthesis. WP3 has provided gait laboratory data for: validating the gait prediction methodology; and informing the concept designs.Planned ImpactThe proposed research addressed three areas (prosthetics, gait simulation and hydraulics-based systems for energy storage and return), and involved both computational modelling and experimental work with amputee subjects. This will have major and broad impact on a range of beneficiaries.