The nervous system is faced with numerous strategies for recruiting a large number of motor units within and among muscle synergists to produce and control body movement. This is challenging, considering multiple combinations of motor unit recruitment may result in the same movement. Yet vertebrates are capable of performing a wide range of movement tasks with different mechanical demands. In this study, we used an experimental human cycling paradigm and musculoskeletal simulations to test the theory that a strategy of prioritizing the minimization of the metabolic cost of muscle contraction, which improves mechanical efficiency, governs the recruitment of motor units within a muscle and the coordination among synergist muscles within the limb. Our results support our hypothesis, for which measured muscle activity and model-predicted muscle forces in soleus—the slower but stronger ankle plantarflexor—is favoured over the weaker but faster medial gastrocnemius (MG) to produce plantarflexor force to meet increased load demands. However, for faster-contracting speeds induced by faster-pedalling cadence, the faster MG is favoured. Similar recruitment patterns were observed for the slow and fast fibres within each muscle. By contrast, a commonly used modelling strategy that minimizes muscle excitations failed to predict force sharing and known physiological recruitment strategies, such as orderly motor unit recruitment. Our findings illustrate that this common strategy for recruiting motor units within muscles and coordination between muscles can explain the control of the plantarflexor muscles across a range of mechanical demands.

中文翻译：

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跨踝伸肌和机械需求之间的任务依赖性募集是由肌肉收缩的代谢成本驱动的

神经系统面临着多种策略，用于在肌肉增效剂内和肌肉增效剂之间募集大量运动单位以产生和控制身体运动。这是具有挑战性的，考虑到运动单位募集的多种组合可能会导致相同的运动。然而，脊椎动物能够执行具有不同机械要求的广泛运动任务。在这项研究中，我们使用了一个实验性的人类骑行范式和肌肉骨骼模拟来测试这样一种理论，即优先考虑最小化肌肉收缩的代谢成本的策略，从而提高机械效率，控制肌肉内运动单位的募集和协调在肢体内的协同肌肉中。我们的结果支持我们的假设，为此，比目鱼肌中测量的肌肉活动和模型预测的肌肉力量（较慢但较强的踝关节跖屈肌）优于较弱但较快的内侧腓肠肌 (MG)，以产生跖屈肌力以满足增加的负荷需求。然而，对于由更快的踏板节奏引起的更快的收缩速度，更快的 MG 是有利的。对于每块肌肉内的慢速和快速纤维，观察到类似的募集模式。相比之下，最小化肌肉兴奋的常用建模策略未能预测力共享和已知的生理募集策略，例如有序的运动单位募集。