Running economy is an important determinant of endurance running performance, yet insights into characteristics contributing to its inter‐individual variability remain limited. Although slow‐twitch muscle fibers are more energy‐efficient than fast‐twitch fibers during the (near‐)isometric contractions common during submaximal running, current literature lacks a consensus on whether a relationship between muscle fiber–type distribution and running economy exists. This study aims to resolve the ongoing debate by addressing potential confounding factors often overlooked in prior research, such as the effect of different running speeds, the homogeneity of investigated groups, and the potential impact of the adopted running gait. We selected two groups with predetermined distinct muscle fiber–type distribution in their triceps surae muscle by measurement of carnosine via 1H‐MRS, one predominantly slow (ST; n = 11; carnosine z‐score = −1.31) and the other predominantly fast (FT; n = 10; z‐score = 0.83). Across a range of running speeds (2–4 m/s), we measured running economy (W/kg) through indirect calorimetry, along with running kinematics, kinetics and muscle activity of the lower limb. The ST‐group exhibited, on average, 7.8% better running economy than the FT‐group (p = 0.01) and this difference was consistent across speeds. Both groups demonstrated almost identical kinematics, kinetics, and muscle activity patterns across submaximal running speeds. Overall, our findings indicate that distinct muscle fiber–type distribution explains some of the observed variability in running economy, for which a predominance of energy‐efficient slow‐twitch fibers appear beneficial. In contrast, muscle fiber–type distribution does not affect running gait substantially.

中文翻译：

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肌肉纤维类型分布的个体间变异性会影响跑步经济性，但不会影响次最大跑步速度的跑步步态


跑步经济性是耐力跑成绩的重要决定因素，但对导致其个体间变异性的特征的了解仍然有限。尽管在次最大跑步期间常见的（近）等长收缩期间，慢肌纤维比快肌纤维更节能，但目前的文献对肌肉纤维类型分布与跑步经济性之间是否存在关系缺乏共识。本研究旨在通过解决先前研究中经常被忽视的潜在混杂因素来解决正在进行的争论，例如不同跑步速度的影响、所研究群体的同质性以及采用跑步步态的潜在影响。我们通过 1H-MRS 测量肌肽，选择了两组在小腿三头肌中具有预定不同肌肉纤维类型分布的组，一组主要是慢的 （ST;n = 11;肌肽 z 评分 = -1.31），另一组主要是快的 （FT;n = 10;z 评分 = 0.83）。在一系列跑步速度 （2-4 m/s） 中，我们通过间接量热法测量了跑步经济性 （W/kg），以及跑步运动学、动力学和下肢的肌肉活动。ST 组的跑步经济性平均比 FT 组高 7.8% （p = 0.01），并且这种差异在速度上是一致的。两组在次最大跑步速度下表现出几乎相同的运动学、动力学和肌肉活动模式。总体而言，我们的研究结果表明，不同的肌肉纤维类型分布解释了观察到的跑步经济性的一些可变性，为此，节能慢肌纤维的优势似乎是有益的。相比之下，肌肉纤维型分布不会对跑步步态产生重大影响。