A Simple Model to Estimate Plantarflexor Muscle-Tendon Mechanics and Energetics During Walking With Elastic Ankle Exoskeletons.
A Simple Model to Estimate Plantarflexor Muscle-Tendon Mechanics and Energetics During Walking With Elastic Ankle Exoskeletons.
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DOI：
10.1109/tbme.2015.2491224
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发表时间：
2016-05
期刊：
影响因子：
--
通讯作者：
Khan NS
中科院分区：
文献类型：
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作者：
Sawicki GS;Khan NS
最近的一项实验表明，当人类穿戴具有中等弹簧硬度的无动力弹性脚踝外骨骼时，他们可以将步行的代谢能量成本降低约7%。太顺从或太僵硬的弹簧几乎没有什么好处。这项研究的目的是使用建模和模拟来探索外骨骼辅助行走中僵硬的“甜蜜点”的肌肉水平机制。我们开发了一个简单的单关节单关节肌肉骨骼模型，它与弹性的‘外肌腱’平行运作。使用具有约束运动学和动力学的逆方法，我们快速模拟了人类在一系列外骨骼刚性值范围内行走，并研究了生物足底屈肌的神经力学和能量学基础。脚踝外骨骼弹簧越僵硬，足屈肌力、活动和新陈代谢能量消耗的下降幅度就越大。然而，在卸载顺应性生物肌肉-肌腱单元(MTU)的过程中，肌束(CE)经历了更大的漂移，这对系列弹性元件(SEE)产生了负面影响，而系列弹性元件(SEE)是一种可调“弹射机构”的特征。肌腱动力学紊乱，以及需要产生补偿力/力矩以保持整体的踝关节力矩不变，这两个因素的结合可以解释在踝关节外骨骼僵硬程度处于中等水平时的新陈代谢表现的“最佳状态”。未来的工作将致力于提供实验证据，以支持本文提出的模型预测，使用超声成像的肌肉水平动力学在步行时使用弹性脚踝外骨骼。工程师必须考虑外骨骼设计的肌肉水平效应，以实现最大性能目标。
A recent experiment demonstrated that when humans wear unpowered elastic ankle exoskeletons with intermediate spring stiffness they can reduce their metabolic energy cost to walk by ~7%. Springs that are too compliant or too stiff have little benefit. The purpose of this study was to use modeling and simulation to explore the muscle-level mechanisms for the ‘sweet-spot’ in stiffness during exoskeleton assisted walking. We developed a simple lumped, uniarticular musculoskeletal model of the plantarflexors operating in parallel with an elastic ‘exo-tendon’. Using an inverse approach with constrained kinematics and kinetics, we rapidly simulated human walking over a range of exoskeleton stiffness values and examined the underlying neuromechanics and energetics of the biological plantarflexors. Stiffer ankle exoskeleton springs resulted in larger decreases in plantarflexor muscle forces, activations and metabolic energy consumption. However, in the process of unloading the compliant biological muscle-tendon unit (MTU), the muscle fascicles (CE) experienced larger excursions that negatively impacted series elastic element (SEE) recoil that is characteristic of a tuned ‘catapult mechanism’. The combination of disrupted muscle-tendon dynamics and the need to produce compensatory forces/moments to maintain overall net ankle moment invariance could explain the ‘sweet spot’ in metabolic performance at intermediate ankle exoskeleton stiffness. Future work will aim to provide experimental evidence to support the model predictions presented here using ultrasound imaging of muscle-level dynamics during walking with elastic ankle exoskeletons. Engineers must account for the muscle-level effects of exoskeleton designs in order to achieve maximal performance objectives.