BACKGROUND The human ankle joint has an influential role in the regulation of the mechanics and energetics of gait. The human ankle can modulate its joint 'quasi-stiffness' (ratio of plantarflexion moment to dorsiflexion displacement) in response to various locomotor tasks (e.g., load carriage). However, the direct effect of ankle stiffness on metabolic energy cost during various tasks is not fully understood. The purpose of this study was to determine how net metabolic energy cost was affected by ankle stiffness while walking under different force demands (i.e., with and without additional load). METHODS Individuals simulated an amputation by using an immobilizer boot with a robotic ankle-foot prosthesis emulator. The prosthetic emulator was controlled to follow five ankle stiffness conditions, based on literature values of human ankle quasi-stiffness. Individuals walked with these five ankle stiffness settings, with and without carrying additional load of approximately 30% of body mass (i.e., ten total trials). RESULTS Within the range of stiffness we tested, the highest stiffness minimized metabolic cost for both load conditions, including a ~ 3% decrease in metabolic cost for an increase in stiffness of about 0.0480 Nm/deg/kg during normal (no load) walking. Furthermore, the highest stiffness produced the least amount of prosthetic ankle-foot positive work, with a difference of ~ 0.04 J/kg from the highest to lowest stiffness condition. Ipsilateral hip positive work did not significantly change across the no load condition but was minimized at the highest stiffness for the additional load conditions. For the additional load conditions, the hip work followed a similar trend as the metabolic cost, suggesting that reducing positive hip work can lower metabolic cost. CONCLUSION While ankle stiffness affected the metabolic cost for both load conditions, we found no significant interaction effect between stiffness and load. This may suggest that the importance of the human ankle's ability to change stiffness during different load carrying tasks may not be driven to minimize metabolic cost. A prosthetic design that can modulate ankle stiffness when transitioning from one locomotor task to another could be valuable, but its importance likely involves factors beyond optimizing metabolic cost.

中文翻译：

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踝关节僵硬对负重行走力学和能量学的影响：假肢模拟器研究。

背景技术人类踝关节在步态力学和能量学的调节中具有重要作用。人类踝关节可以响应各种运动任务（例如，负载运输）来调节其关节“准刚度”（跖屈力矩与背屈位移的比率）。然而，踝关节僵硬对各种任务期间代谢能量消耗的直接影响尚不完全清楚。本研究的目的是确定在不同的力量需求（即有和没有额外负荷）下行走时踝关节僵硬如何影响净代谢能量消耗。方法 个人使用带有机器人踝足假肢模拟器的固定靴来模拟截肢。根据人类踝关节准刚度的文献值，控制假肢模拟器遵循五种踝关节刚度条件。个人以这五种踝关节刚度设置行走，携带或不携带大约体重 30% 的额外负载（即总共十次试验）。结果 在我们测试的刚度范围内，最高刚度可最大限度地降低两种负载条件下的代谢成本，包括在正常（无负载）行走期间，刚度增加约 0.0480 Nm/deg/kg，代谢成本降低约 3%。此外，最高刚度产生的假肢踝足正功最少，最高刚度条件与最低刚度条件之间的差异约为 0.04 J/kg。同侧髋部正功在无负载条件下没有显着变化，但在附加负载条件下在最高刚度下最小化。对于额外负荷条件，髋部做功遵循与代谢成本相似的趋势，表明减少髋部积极做功可以降低代谢成本。结论虽然踝关节僵硬会影响两种负载条件下的代谢成本，但我们发现僵硬和负载之间没有显着的相互作用。这可能表明，人类脚踝在不同的负重任务期间改变刚度的能力的重要性可能不会被驱动以最小化代谢成本。当从一项运动任务过渡到另一项运动任务时，可以调节踝关节硬度的假肢设计可能很有价值，但其重要性可能涉及优化代谢成本之外的因素。