Abstract
BackgroundHumans normally dissipate significant energy during walking, largely at the transitions between steps. The ankle then acts to restore energy during push-off, which may be the reason that ankle impairment nearly always leads to poorer walking economy. The replacement of lost energy is necessary for steady gait, in which mechanical energy is constant on average, external dissipation is negligible, and no net work is performed over a stride. However, dissipation and replacement by muscles might not be necessary if energy were instead captured and reused by an assistive device.Methodology/Principal FindingsWe developed a microprocessor-controlled artificial foot that captures some of the energy that is normally dissipated by the leg and “recycles” it as positive ankle work. In tests on subjects walking with an artificially-impaired ankle, a conventional prosthesis reduced ankle push-off work and increased net metabolic energy expenditure by 23% compared to normal walking. Energy recycling restored ankle push-off to normal and reduced the net metabolic energy penalty to 14%.Conclusions/SignificanceThese results suggest that reduced ankle push-off contributes to the increased metabolic energy expenditure accompanying ankle impairments, and demonstrate that energy recycling can be used to reduce such cost.
Highlights
The ankle normally produces a larger burst of work than any other joint during walking [1]
Conclusions/Significance: These results suggest that reduced ankle push-off contributes to the increased metabolic energy expenditure accompanying ankle impairments, and demonstrate that energy recycling can be used to reduce such cost
Normal walking yielded an average rate of ankle push-off work of 17.763.4 W
Summary
The ankle normally produces a larger burst of work than any other joint during walking [1]. We developed an energy-recycling artificial foot (Figure 2, Movie S1) that captures collision energy and returns it for push-off. Active control of energy storage and return distinguishes this device from conventional prosthetic feet with passive elastic elements, which have not been found to significantly reduce the metabolic penalty of walking with ankle impairment [5,6,7], while low electrical power requirements distinguish it from other robotic prostheses [10].
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