Department of Public Health, Aarhus University, Dalgas Avenue 4, Aarhus C, 8000, Aarhus, Denmark.
Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada.
Pflugers Arch. 2020 May;472(5):597-608. doi: 10.1007/s00424-020-02390-5. Epub 2020 May 15.
The power of shortening contractions in skeletal muscle is determined by the force-velocity relationship. Fatigue has been reported to either increase or decrease the force-velocity curvature depending on experimental circumstances. These discrepant findings may be related to experimental differences in oxygen availability. We therefore investigated how the curvature of the force-velocity relationship in soleus and gastrocnemius rat muscles is affected during fatigue, in both an ex vivo setup without an intact blood perfusion and in an in situ setup with an intact blood perfusion. Furthermore, we investigated the effect of reduced oxygen concentrations and reduced diffusion distance on the curvature of the force-velocity relationship in ex vivo muscles, where muscle oxygen uptake relies on diffusion from the incubation medium. Muscles were electrically stimulated to perform repeated shortening contractions and force-velocity curves were determined in rested and fatigued conditions. The curvature increased during fatigue in the soleus muscles (both in situ and ex vivo), and decreased for the gastrocnemius muscles (in situ) or remained unchanged (ex vivo). Furthermore, under ex vivo conditions, neither reduced oxygen concentrations nor reduced diffusion distance conferred any substantial effect on the force-velocity curvature. In contrast, reduced oxygen availability and increased diffusion distance did increase the loss of maximal power during fatigue, mainly due to additional decreases in isometric force. We conclude that oxygen availability does not influence the fatigue-induced changes in force-velocity curvature. Rather, the observed variable fatigue profiles with regard to changes in curvature seem to be linked to the muscle fiber-type composition.
缩短骨骼肌收缩的力量取决于力-速度关系。疲劳可导致力-速度曲线的曲率增加或减小，这取决于实验条件。这些不一致的发现可能与氧可用性的实验差异有关。因此，我们研究了在没有完整血液灌注的离体设置和具有完整血液灌注的原位设置下，在疲劳过程中，大鼠比目鱼肌和腓肠肌的力-速度关系的曲率如何受到影响。此外，我们还研究了氧浓度降低和扩散距离缩短对离体肌肉力-速度关系曲率的影响，其中肌肉氧摄取依赖于从孵育介质中的扩散。肌肉通过电刺激进行重复的缩短收缩，并在休息和疲劳条件下确定力-速度曲线。在比目鱼肌（原位和离体）中，曲率在疲劳过程中增加，而在腓肠肌（原位）中减小或保持不变（离体）。此外，在离体条件下，降低氧浓度或降低扩散距离都不会对力-速度曲线的曲率产生实质性影响。相比之下，降低氧可用性和增加扩散距离确实会增加疲劳过程中最大力量的损失，主要是由于等长力量的进一步降低。我们得出结论，氧可用性不会影响疲劳引起的力-速度曲线变化。相反，观察到的关于曲率变化的可变疲劳模式似乎与肌肉纤维类型组成有关。
