Muscles are biological actuators extensively studied in the frame of Hill’s classic empirical model as isolated biomechanical entities, which hardly applies to a living organism subjected to physiological and environmental constraints. Here we elucidate the overarching principle of a muscle action for locomotion, considering it from the thermodynamic viewpoint as an assembly of actuators (muscle units) connected in parallel, operating via chemical-to-mechanical energy conversion under mixed (potential and flux) boundary conditions. Introducing the energy cost of effort, $CO{E}_{-}$, as the generalization of the well-known oxygen cost of transport, $COT$, in the frame of our compact locally linear non-equilibrium thermodynamics model, we analyze oxygen consumption measurement data from a documented experiment on energy cost management and optimization by horses moving at three different gaits. Horses adapt to a particular gait by mobilizing a nearly constant number of muscle units minimizing waste production per unit distance covered; this number significantly changes during transition between gaits. The mechanical function of the animal is therefore determined both by its own thermodynamic characteristics and by the metabolic operating point of the locomotor system.

中文翻译：

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动物运动的热力学

肌肉是在希尔（Hill）经典经验模型的框架中作为孤立的生物力学实体而被广泛研究的生物促动器，它几乎不适用于受到生理和环境限制的活生物体。在这里，我们从运动力学的角度出发，阐明了运动的肌肉动作的总体原理，将其看作是并联连接的执行器（肌肉单元）的组合体，在混合（势能和通量）边界条件下通过化学-机械能转换进行操作。介绍了精力消耗的能量，$CØ{Ë}_{-}$，作为众所周知的氧气运输成本的概括， $CØŤ$，在我们紧凑的局部线性非平衡热力学模型的框架内，我们分析了有记录的能源成本管理实验的耗氧量测量数据，该实验由马在三种不同步态下移动进行。马通过动员几乎恒定数量的肌肉单位来适应特定的步态，从而最大程度地减少单位覆盖距离内的废物产生；在步态之间的过渡期间，此数字会发生显着变化。因此，动物的机械功能既取决于其自身的热力学特性，又取决于运动系统的代谢工作点。