Paglietti A
Department of Mechanical, Chemical and Materials Engineering, University of Cagliari, 09123, Cagliari, Italy.
J Biol Phys. 2018 Dec;44(4):619-646. doi: 10.1007/s10867-018-9510-y. Epub 2018 Oct 2.
Like any other kind of cell, muscle cells produce energy by oxidizing the fuel substrate that they absorb together with the needed oxygen from the surroundings. Oxidation occurs entirely within the cell. It means that the reactants and products of reaction must at some time be dissolved in the cell's cytosol. If a cell operates at steady state, its cytosol composition remains constant. Therefore, the cytosol in a muscle that produces work at steady state must contain a constant amount of fuel, oxygen, and product of reaction dissolved in it. The greater the power produced, the higher the concentration of these solutes. There is a limit, however, to the maximum amount of solutes that the cytosol can contain without damaging the cell. General thermodynamic arguments, which are reviewed in this paper, help relate this limit to the dehydration and overhydration limits of the cell. The present analysis shows that the same limits entail a limit to the maximum power that a muscle can produce at steady state. This limit depends on the composition of the fuel mixture used by the muscle. The analysis also determines the number of fuel carbon atoms that must be oxidized in parallel within a cell to produce a given power. It may well happen that a muscle cannot reach the maximum attainable power because it cannot activate all the parallel oxidation paths that are needed to produce it. This may be due to a series of reasons ranging from health issues to a lack of training. The paper shows how the methods of indirect calorimetry can provide all the experimental data needed to determine the actual number of parallel oxidation paths that at steady state must be active in a muscle in a given exercise. A diagram relating muscle power to the number of parallel oxidation paths and fuel composition is finally presented. It provides a means to assess the power capacity of animal muscles and can be applied to evaluate their fitness, stamina, margins for improvement, and athletic potential.
与其他任何类型的细胞一样，肌肉细胞通过氧化它们从周围环境中吸收的燃料底物以及所需的氧气来产生能量。氧化完全在细胞内发生。这意味着反应的反应物和产物在某个时候必须溶解在细胞的胞质溶胶中。如果细胞处于稳定状态运行，其胞质溶胶组成保持恒定。因此，在稳定状态下产生功的肌肉中的胞质溶胶必须含有溶解在其中的恒定数量的燃料、氧气和反应产物。产生的功率越大，这些溶质的浓度就越高。然而，胞质溶胶在不损害细胞的情况下能够容纳的溶质最大量是有限的。本文回顾的一般热力学论点有助于将这个限度与细胞的脱水和水合过度限度联系起来。目前的分析表明，这些相同的限度对肌肉在稳定状态下能够产生的最大功率也构成了限制。这个限度取决于肌肉使用的燃料混合物的组成。该分析还确定了在细胞内必须并行氧化的燃料碳原子数量，以产生给定的功率。很可能会出现肌肉无法达到可达到的最大功率的情况，因为它无法激活产生该功率所需的所有并行氧化途径。这可能是由于从健康问题到缺乏训练等一系列原因造成的。本文展示了间接量热法如何能够提供所有所需的实验数据，以确定在给定运动中肌肉在稳定状态下必须活跃的并行氧化途径的实际数量。最后给出了一个将肌肉功率与并行氧化途径数量和燃料组成相关联的图表。它提供了一种评估动物肌肉功率容量的方法，可用于评估它们的健康状况、耐力、改进空间和运动潜力。
