Effect of push-off timing on metabolic cost during walking with a universal ankle-foot prosthesis emulator

1 Introduction The ankle delivers about half of the total mechanical work during walking. Lower-limb amputees using conventional passive-elastic prostheses experience 20 to 30% higher metabolic cost than able-bodied individuals, perhaps because these prostheses do not provide net positive work during the course of a step [1]. To address this problem, companies are developing battery-powered prostheses (e.g., [2]) that provide net positive push-off work. Simulations of normal walking predict that trailing leg push-off just before collision of the leading leg reduces energy dissipation, thereby reducing overall mechanical work requirements [3]. This is consistent with reductions in metabolic cost observed in an experiment with powered bilateral ankle exoskeletons [4]. In this experiment, however, timing was varied together with push-off work, which also affects metabolic cost [5]. Subjects wearing an exoskeleton in parallel with their ankle could also independently affect total push-off timing and work. Therefore, our goal was to study the isolated effects of varying the timing of total ankle push-off on the energetics and kinetics of human walking. We used a universal ankle-foot prosthesis emulator, which allowed precise control of push-off mechanics.