Supplementary Materials

The tables S1 to S4 in the supplementary material show the results of the sensitivity analysis on the net work of the Sol and gastrocnemii at the ankle joint as well as the net work of the gastrocnemii at the knee joint, which represents the contribution of the biarticular mechanisms to the increase of net ankle work. Different force potentials and ratios of the GM EMG-activity affect the absolute values in all three parameters. Nevertheless, in all combinations, the contribution of the Sol to the net mechanical work at the ankle joint was higher than the gastrocnemii. Both the energy production of the monoarticular Sol and the contribution of the biarticular mechanisms (i.e., in increased net ankle work) increased with walking speed. Thus, the sensitivity analysis clearly demonstrates that the main findings and conclusions generally hold true even under the assumption of varying force-length-velocity potentials and activation of the individual muscles. The video clip illustrates a graphical animation of the right leg during the maximal walking speed of an individual. The vastus lateralis and the gastrocnemii muscles are colored in red, and the soleus in the blue spectrum. Lighter red and blue colors show lower muscle activity, and darker red and blue colors show higher muscle activity. From 47% to 72% of the stance phase, the knee joint extends, and the ankle joint is plantarflexing. This simultaneous knee extension and ankle plantar flexion initiate the energy transfer from the knee extensor to the ankle plantar flexor muscles.

补充材料中的表S1至S4展示了针对踝关节处比目鱼肌（Sol，Soleus）与腓肠肌（gastrocnemii）的净机械功，以及膝关节处腓肠肌净机械功的敏感性分析结果，该结果反映了双关节机制（biarticular mechanisms）对踝关节净功提升的贡献。不同的力势及腓肠肌肌电活动（EMG-activity）比率会影响三个参数的绝对值。尽管如此，在所有参数组合下，比目鱼肌对踝关节净机械功的贡献均高于腓肠肌。单关节（monoarticular）比目鱼肌的能量生成量与双关节机制（即踝关节净功的提升）均随步行速度增加而上升。因此，本敏感性分析明确证实，即使在力-长度-速度特性（force-length-velocity potentials）变化及单块肌肉激活状态改变的假设前提下，本研究的主要发现与结论依然成立。视频片段展示了个体以最大步行速度行走时右腿的可视化动画：股外侧肌（vastus lateralis）与腓肠肌以红色标注，比目鱼肌以蓝色光谱色系标注；色调越浅代表肌肉活动度越低，色调越深则肌肉活动度越高。在站立相（stance phase）的47%至72%期间，膝关节处于伸展状态，踝关节则处于跖屈（plantarflexion）状态，这种同步的膝关节伸展与踝关节跖屈动作，启动了从膝伸肌到踝跖屈肌的能量传递。