Department of Movement Sciences, KU Leuven, Leuven, Belgium.
Department of Movement and Sports Sciences, Ghent University, Ghent, Belgium.
Scand J Med Sci Sports. 2024 Nov;34(11):e14748. doi: 10.1111/sms.14748.
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 H-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.
跑步经济性是耐力跑步表现的一个重要决定因素，但对于导致个体间差异的特征，我们的了解仍然有限。虽然在亚最大强度跑步过程中常见的（近）等长收缩中，慢肌纤维比快肌纤维的能量效率更高，但目前的文献缺乏关于肌肉纤维类型分布与跑步经济性之间是否存在关系的共识。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，例如不同跑步速度的影响、研究对象的同质性以及所采用的跑步步态的潜在影响，来解决这一持续存在的争议。我们通过 H-MRS 测量肌肽，选择了两个预先确定的具有不同比目鱼肌肌肉纤维类型分布的组，一个主要是慢肌（ST；n=11；肌肽 z 分数=-1.31），另一个主要是快肌（FT；n=10；z 分数=0.83）。我们在一系列跑步速度（2-4 m/s）下，通过间接测热法测量跑步经济性（W/kg），以及下肢的跑步运动学、动力学和肌肉活动。ST 组的跑步经济性比 FT 组平均高出 7.8%（p=0.01），且这种差异在不同速度下是一致的。两个组在亚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。总的来说，我们的研究结果表明，不同的肌肉纤维类型分布解释了跑步经济性中观察到的一些可变性，其中以能量效率高的慢肌纤维为主似乎是有益的。相比之下，肌肉纤维类型分布不会对跑步步态产生实质性影响。
