Akagi Ryota, Hinks Avery, Power Geoffrey A
College of Systems Engineering and Science, Shibaura Institute of Technology, Saitama, Japan.
Department of Human Health and Nutritional Sciences, College of Biological Science, University of Guelph, Guelph, Ontario, Canada.
J Appl Physiol (1985). 2020 Jul 1;129(1):173-184. doi: 10.1152/japplphysiol.00280.2020. Epub 2020 Jun 18.
We evaluated the effects of differential muscle architectural adaptations on neuromuscular fatigue resistance. Seven young males and six females participated in this study. Using a longitudinal within-subject design, legs were randomly assigned to perform isometric training of the tibialis anterior (TA) three times per week for 8 wk at a short (S-group) or long muscle-tendon unit length (L-group). Before and following training, fascicle length (FL) and pennation angle (PA) of the TA were assessed. As well, fatigue-related time course changes in isometric maximal voluntary contraction (MVC) torque and isotonic peak power (20% MVC resistance) were determined before, immediately after, and 1, 2, 5, and 10 min following task failure. The fatiguing task consisted of repeated maximal effort isotonic (20% MVC resistance) contractions over a 40° range of motion until the participant reached a 40% reduction in peak power. Although there was no clear improvement in neuromuscular fatigue resistance following training in either group ( = 0.081; S-group: ∼20%; L-group: ∼51%), the change in neuromuscular fatigue resistance was related positively to the training-induced increase in PA (∼6%, < 0.001) in the S-group ( = 0.739, = 0.004) and negatively to the training-induced increase in FL (∼4%, = 0.001) in the L-group ( = -0.568, = 0.043). Both groups recovered similarly for MVC torque and peak power after the fatiguing task as compared with before training. We suggest that the relationships between the changes in muscle architecture and neuromuscular fatigue resistance depend on the muscle-tendon unit lengths at which the training is performed. Eight weeks of isometric training at a long or short muscle-tendon unit length increased and did not change fascicle length, respectively. The "width" of the torque-angle relationship plateau became broader following isometric training at the long length. Despite marked differences in muscle architecture and functional adaptations between the groups, there was only a small-magnitude improvement in neuromuscular fatigue resistance, which was surprisingly negatively related to increased fascicle length in the long length-training group.
我们评估了不同的肌肉结构适应性对神经肌肉抗疲劳能力的影响。七名年轻男性和六名女性参与了本研究。采用纵向自身对照设计，将双腿随机分配，使其以短肌肉 - 肌腱单元长度（S组）或长肌肉 - 肌腱单元长度（L组），每周进行三次胫骨前肌（TA）的等长训练，持续8周。在训练前后，评估TA的肌束长度（FL）和羽状角（PA）。此外，在任务失败前、刚结束后以及结束后1、2、5和10分钟，测定等长最大自主收缩（MVC）扭矩和等张峰值功率（20%MVC阻力）与疲劳相关的时程变化。疲劳任务包括在40°运动范围内重复进行最大努力的等张收缩（20%MVC阻力），直到参与者的峰值功率降低40%。尽管两组训练后神经肌肉抗疲劳能力均无明显改善（P = 0.081；S组：约20%；L组：约51%），但S组神经肌肉抗疲劳能力的变化与训练引起的PA增加（约6%，P < 0.001）呈正相关（r = 0.739，P = 0.004），而L组与训练引起的FL增加（约4%，P = 0.001）呈负相关（r = -0.568，P = 0.043）。与训练前相比，两组在疲劳任务后MVC扭矩和峰值功率的恢复情况相似。我们认为，肌肉结构变化与神经肌肉抗疲劳能力之间的关系取决于训练时的肌肉 - 肌腱单元长度。在长或短肌肉 - 肌腱单元长度下进行8周的等长训练，分别增加和未改变肌束长度。在长肌肉 - 肌腱单元长度下进行等长训练后，扭矩 - 角度关系平台的“宽度”变宽。尽管两组之间在肌肉结构和功能适应性方面存在显著差异，但神经肌肉抗疲劳能力仅有小幅改善，令人惊讶的是，在长长度训练组中，这与肌束长度增加呈负相关。
