Multiple intramuscular variables have been proposed to explain the high variability in resistance training induced muscle hypertrophy across humans. This study investigated if muscular androgen receptor (AR), estrogen receptor α (ERα) and β (ERβ) content and fiber capillarization are associated with fiber and whole‐muscle hypertrophy after chronic resistance training. Male (n = 11) and female (n = 10) resistance training novices (22.1 ± 2.2 years) trained their knee extensors 3×/week for 10 weeks. Vastus lateralis biopsies were taken at baseline and post the training period to determine changes in fiber type specific cross‐sectional area (CSA) and fiber capillarization by immunohistochemistry and, intramuscular AR, ERα and ERβ content by Western blotting. Vastus lateralis volume was quantified by MRI‐based 3D segmentation. Vastus lateralis muscle volume significantly increased over the training period (+7.22%; range: −1.82 to +18.8%, p < 0.0001) but no changes occurred in all fiber (+1.64%; range: −21 to +34%, p = 0.869), type I fiber (+1.33%; range: −24 to +41%, p = 0.952) and type II fiber CSA (+2.19%; range: −23 to +29%, p = 0.838). However, wide inter‐individual ranges were found. Resistance training increased the protein expression of ERα but not ERβ and AR, and the increase in ERα content was positively related to changes in fiber CSA. Only for the type II fibers, the baseline capillary‐to‐fiber‐perimeter index was positively related to type II fiber hypertrophy but not to whole muscle responsiveness. In conclusion, an upregulation of ERα content and an adequate initial fiber capillarization may be contributing factors implicated in muscle fiber hypertrophy responsiveness after chronic resistance training.

中文翻译：

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肌内类固醇受体含量及纤维毛细血管化对骨骼肌肥大的影响


多个肌内变量被提出来解释人类抗阻训练引起的肌肉肥大的高度变异性。本研究调查了肌肉雄激素受体 (AR)、雌激素受体 α (ERα) 和 β (ERβ) 含量以及纤维毛细血管化是否与慢性阻力训练后纤维和全肌肉肥大相关。男性 （ n = 11) 和女性 ( n = 10) 阻力训练新手（22.1 ± 2.2 岁）每周训练膝关节伸肌 3 次，持续 10 周。在基线和训练期后进行股外侧肌活检，通过免疫组织化学测定纤维类型特定横截面积（CSA）和纤维毛细血管化的变化，并通过蛋白质印迹测定肌内 AR、ERα 和 ERβ 含量。通过基于 MRI 的 3D 分割对股外侧肌体积进行量化。训练期间股外侧肌体积显着增加（+7.22%；范围：-1.82 至 +18.8%， p < 0.0001），但所有纤维均未发生变化（+1.64%；范围：-21 至 +34%， p = 0.869），I 型纤维（+1.33%；范围：−24 至 +41%， p = 0.952）和 II 型光纤 CSA（+2.19%；范围：−23 至 +29%， p = 0.838）。然而，发现了广泛的个体差异。抗阻训练增加了ERα的蛋白表达，但不增加ERβ和AR的蛋白表达，且ERα含量的增加与纤维CSA的变化呈正相关。仅对于 II 型纤维，基线毛细血管-纤维周长指数与 II 型纤维肥大呈正相关，但与整个肌肉反应性无关。 总之，ERα含量的上调和充分的初始纤维毛细化可能是慢性阻力训练后肌纤维肥大反应性的影响因素。