Data from: Muscle-tendon mechanics explain unexpected effects of exoskeleton assistance on metabolic rate during walking

The goal of this study was to gain insight into how ankle exoskeletons affect the behavior of the plantarflexor muscles during walking. Using data from previous experiments, we performed electromyography-driven simulations of musculoskeletal dynamics to explore how changes in exoskeleton assistance affected plantarflexor muscle–tendon mechanics, particularly for the soleus. We used a model of muscle energy consumption to estimate individual muscle metabolic rate. As average exoskeleton torque was increased, while no net exoskeleton work was provided, a reduction in tendon recoil led to an increase in positive mechanical work performed by the soleus muscle fibers. As net exoskeleton work was increased, both soleus muscle fiber force and positive mechanical work decreased. Trends in the sum of the metabolic rates of the simulated muscles correlated well with trends in experimentally observed whole-body metabolic rate (R2=0.9), providing confidence in our model estimates. Our simulation results suggest that different exoskeleton behaviors can alter the functioning of the muscles and tendons acting at the assisted joint. Furthermore, our results support the idea that the series tendon helps reduce positive work done by the muscle fibers by storing and returning energy elastically. We expect the results from this study to promote the use of electromyography-driven simulations to gain insight into the operation of muscle–tendon units and to guide the design and control of assistive devices.本研究旨在解析踝关节外骨骼（ankle exoskeletons）在行走过程中对跖屈肌（plantarflexor muscles）功能的影响机制。研究团队依托既往实验采集的数据，开展了针对肌肉骨骼动力学（musculoskeletal dynamics）的肌电驱动仿真（electromyography-driven simulations），以探究外骨骼辅助参数变化对跖屈肌肌腱力学特性的影响，尤其聚焦于比目鱼肌（soleus）。本研究采用肌肉能量消耗模型，对单块肌肉的代谢率（metabolic rate）进行估算：当外骨骼平均扭矩升高且未提供净外骨骼功时，肌腱回弹（tendon recoil）量的减少会使比目鱼肌肌纤维的正机械功（positive mechanical work）输出增加；而当外骨骼净功提升时，比目鱼肌肌纤维的受力与正机械功均出现下降。仿真肌肉代谢率总和的变化趋势，与实验观测得到的全身代谢率变化趋势高度相关（R²=0.9），证实了本模型估算结果的可靠性。本研究的仿真结果表明，不同的外骨骼工作模式可改变受辅助关节处肌肉与肌腱的运作功能。此外，本研究结果支持了串联肌腱（series tendon）可通过弹性储能与释能，降低肌纤维所需完成的正机械功这一学术观点。本研究预期成果将推动肌电驱动仿真技术在解析肌腱单元（muscle-tendon units）运作机制，以及指导辅助装置（assistive devices）设计与控制领域的应用。