BACKGROUND Eccentric training, such as Nordic hamstring exercise (NHE) training, is commonly used as a preventive measure for hamstring strains. Eccentric training is believed to induce lengthening of muscle fascicles and to be associated with the addition of sarcomeres in series within muscle fibers. However, the difficulty in measuring sarcomere adaptation in human muscles has severely limited information about the precise mechanisms of adaptation. This study addressed this limitation by measuring the multiscale hamstring muscle adaptations in response to 9 weeks of NHE training and 3 weeks of detraining. METHODS Twelve participants completed 9 weeks of supervised NHE training, followed by a 3-week detraining period. We assessed biceps femoris long-head (BFlh) muscle fascicle length, sarcomere length, and serial sarcomere number in the central and distal regions of the muscle. Additionally, we measured muscle volume and eccentric strength at baseline, post-training, and post-detraining. RESULTS NHE training over 9 weeks induced significant architectural and strength adaptations in the BFlh muscle. Fascicle length increased by 19% in the central muscle region and 33% in the distal muscle region. NHE also induced increases in serial sarcomere number (25% in the central region and 49% in the distal region). BFlh muscle volume increased by 8%, and knee flexion strength increased by 40% with training. Following 3 weeks of detraining, fascicle length decreased by 12% in the central region and 16% in the distal region along with reductions in serial sarcomere number. CONCLUSION Nine weeks of NHE training produced substantial, region-specific increases in BFlh muscle fascicle length, muscle volume, and force generation. The direct measurement of sarcomere lengths revealed that the increased fascicle length was accompanied by the addition of sarcomeres in series within the muscle fascicles.

中文翻译：

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离心训练 9 周后的多尺度腘绳肌适应。


背景 离心训练，例如北欧腘绳肌运动 （NHE） 训练，通常用作腘绳肌拉伤的预防措施。离心训练被认为会引起肌肉束的延长，并与肌肉纤维内串联的肌节有关。然而，测量人体肌肉肌节适应的困难严重限制了有关适应确切机制的信息。本研究通过测量响应 9 周 NHE 训练和 3 周停止训练的多尺度腘绳肌适应来解决这一限制。方法 12 名参与者完成了 9 周的监督 NHE 培训，然后是 3 周的停止培训期。我们评估了肌肉中央和远端区域的股二头肌长头 （BFlh） 肌肉束长度、肌节长度和序列肌节数量。此外，我们还测量了基线、训练后和训练后离心力量的肌肉体积和离心力量。结果 超过 9 周的 NHE 训练诱导了 BFlh 肌肉的显着结构和力量适应。中央肌区束长增加 19%，远端肌区束长增加 33%。NHE 还诱导了连续肌节数量的增加 （中央区 25%，远端区 49%）。训练后，BFlh 肌肉体积增加了 8%，膝关节屈曲力量增加了 40%。停止训练 3 周后，中央区束长减少 12%，远端区束长减少 16%，同时序列肌节数量减少。结论 9 周的 NHE 训练使 BFlh 肌肉束长度、肌肉体积和力量产生产生了显着的、区域特异性的增加。 肌节长度的直接测量表明，束长度的增加伴随着肌肉束内串联的肌节的增加。