The effects of ankle stiffness on mechanics and energetics of walking with added loads: a prosthetic emulator study.
Erica A Hedrick, Philippe Malcolm, Jason M Wilken and 1 others
PMID 31752942WHAT IT FOUND
In healthy adults simulating an amputation, stiffer prosthetic ankles reduced metabolic cost, contradicting the hypothesis that lower stiffness is better.
However, the effect was small, and participants perceived higher stiffness as more difficult when carrying loads.
Key findings
01Contrary to the hypothesis, the highest stiffness tested minimized metabolic energy for both normal walking and load carriage.
02There was no significant interaction between stiffness and load on metabolic energy cost, suggesting that modulating stiffness like the human ankle may not provide metabolic benefit.
03Participants did not perceive differences in stiffness during unloaded walking but found increasing stiffness more unnatural and difficult when carrying additional load.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTsWhat it means for SLPs
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What it does not show
The study used healthy individuals simulating an amputation with a boot, which may not accurately reflect the mechanics or comfort of people with actual amputations. The range of stiffness tested was narrow and centered around typical human values; wider ranges might have revealed different optimal settings. The prosthesis had no articulation in the foot or toes, unlike the human foot, which may have skewed the results toward higher ankle stiffness. The metabolic differences observed were very small and likely not clinically meaningful. Participants were inexperienced with the device, and familiarity with load carriage was not assessed.
Declared interests
The study was funded by the National Institutes of Health, the University of Nebraska at Omaha, and the Nebraska Space Grant Consortium. No other conflicts of interest are reported in the provided text.
The easy way to misread this
Do not assume that stiffer prosthetic ankles are clinically superior for patients with amputations. The study used healthy individuals simulating an amputation, the metabolic benefits were negligible, and participants actually found higher stiffness more difficult to tolerate when carrying loads.