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. <br> 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）与腓肠肌的净力学功，以及膝关节处腓肠肌的净力学功的敏感性分析结果，该结果反映了双关节机制对踝关节净功提升的贡献。不同的力势以及腓肠肌内侧（GM）肌电活动比率，会影响三个参数的绝对数值。尽管如此，在所有参数组合下，比目鱼肌对踝关节净力学功的贡献均高于腓肠肌。单关节比目鱼肌的能量生成量，以及双关节机制（即对踝关节净功的提升贡献）均随步行速度增加而上升。因此，本次敏感性分析明确证实，即便在力-长度-速度势变化以及单块肌肉激活程度改变的假设条件下，本研究的核心发现与结论依然普遍成立。
本视频片段展示了某个体以最大步行速度运动时的右腿动态动画。股外侧肌与腓肠肌以红色标识，比目鱼肌则以蓝色光谱色系标识。颜色越浅的红、蓝色代表肌肉活动度越低，颜色越深则代表肌肉活动度越高。在步态站立相的47%至72%阶段，膝关节处于伸展状态，踝关节处于跖屈状态。这种膝关节伸展与踝关节跖屈的同步动作，启动了从膝伸肌到踝跖屈肌的能量传递。