School of Human Movement and Nutrition Sciences, Centre for Sensorimotor Performance, The University of Queensland, Brisbane, Queensland, Australia.
School of Health and Wellbeing, University of Southern Queensland, Brisbane, Queensland, Australia.
Scand J Med Sci Sports. 2018 Oct;28(10):2123-2134. doi: 10.1111/sms.13222. Epub 2018 Jun 7.
Changes in muscle fascicle mechanics have been postulated to underpin the repeated bout effect (RBE) observed following exercise-induced muscle damage (EIMD). However, in the medial gastrocnemius (MG), mixed evidence exists on whether fascicle stretch amplitude influences the level of EIMD, thus questioning whether changes in fascicle mechanics underpin the RBE. An alternative hypothesis is that neural adaptations contribute to the RBE in this muscle. The aim of this study was to investigate the neuromechanical adaptations during and after repeated bouts of a highly controlled muscle lengthening exercise that aimed to maximize EIMD in MG. In all, 20 subjects performed two bouts of 500 active lengthening contractions (70% of maximal activation) of the triceps surae, separated by 7 days. Ultrasound constructed fascicle length-torque (L-T) curves of MG, surface electromyography (EMG), maximum torque production, and muscle soreness were assessed before, 2 hours and 2 days after each exercise bout. The drop in maximum torque (4%) and the increase in muscle soreness (24%) following the repeated bout were significantly less than following the initial bout (8% and 59%, respectively), indicating a RBE. However, neither shift in the L-T curve nor changes in EMG parameters were present. Furthermore, muscle properties during the exercise were not related to the EIMD or RBE. Our results show that there are no global changes in gastrocnemius mechanical behavior or neural activation that could explain the observed RBE in this muscle. We suggest that adaptations in the non-contractile elements of the muscle are likely to explain the RBE in the triceps surae.
肌肉肌束力学的变化被认为是运动引起的肌肉损伤 (EIMD) 后观察到的重复回合效应 (RBE) 的基础。然而，在内侧腓肠肌 (MG) 中，关于肌束拉伸幅度是否影响 EIMD 水平存在混合证据，因此质疑肌束力学的变化是否是 RBE 的基础。另一种假设是，神经适应有助于该肌肉的 RBE。本研究旨在研究在重复进行高度受控的肌肉延长运动后的神经力学适应，该运动旨在最大限度地引起 MG 中的 EIMD。总共 20 名受试者进行了两回合的 500 次主动延长收缩（最大激活的 70%），间隔 7 天。在每次运动回合之前、2 小时和 2 天后，使用超声构建的 MG 肌束长度-扭矩 (L-T) 曲线、表面肌电图 (EMG)、最大扭矩产生和肌肉酸痛进行评估。与初始回合相比，重复回合后最大扭矩下降（4%）和肌肉酸痛增加（24%）明显较小，表明存在 RBE。然而，L-T 曲线的偏移或 EMG 参数的变化都不存在。此外，运动过程中的肌肉特性与 EIMD 或 RBE 无关。我们的结果表明，MG 中没有可以解释观察到的 RBE 的整体肌肉力学行为或神经激活变化。我们认为，肌肉非收缩成分的适应可能解释了三腿肌中的 RBE。
