Department of Movement and Sports Sciences, Ghent University, Ghent, Belgium.
Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark.
J Physiol. 2023 Jun;601(12):2307-2327. doi: 10.1113/JP284442. Epub 2023 Apr 26.
Considerable inter-individual heterogeneity exists in the muscular adaptations to resistance training. It has been proposed that fast-twitch fibres are more sensitive to hypertrophic stimuli and thus that variation in muscle fibre type composition is a contributing factor to the magnitude of training response. This study investigated if the inter-individual variability in resistance training adaptations is determined by muscle typology and if the most appropriate weekly training frequency depends on muscle typology. In strength-training novices, 11 slow (ST) and 10 fast typology (FT) individuals were selected by measuring muscle carnosine with proton magnetic resonance spectroscopy. Participants trained both upper arm and leg muscles to failure at 60% of one-repetition maximum (1RM) for 10 weeks, whereby one arm and leg trained 3×/week and the contralateral arm and leg 2×/week. Muscle volume (MRI-based 3D segmentation), maximal dynamic strength (1RM) and fibre type-specific cross-sectional area (vastus lateralis biopsies) were evaluated. The training response for total muscle volume (+3 to +14%), fibre size (-19 to +22%) and strength (+17 to +47%) showed considerable inter-individual variability, but these could not be attributed to differences in muscle typology. However, ST individuals performed a significantly higher training volume to gain these similar adaptations than FT individuals. The limb that trained 3×/week had generally more pronounced hypertrophy than the limb that trained 2×/week, and there was no interaction with muscle typology. In conclusion, muscle typology cannot explain the high variability in resistance training adaptations when training is performed to failure at 60% of 1RM. KEY POINTS: This study investigated the influence of muscle typology (muscle fibre type composition) on the variability in resistance training adaptations and on its role in the individualization of resistance training frequency. We demonstrate that an individual's muscle typology cannot explain the inter-individual variability in resistance training-induced increases in muscle volume, maximal dynamic strength and fibre cross-sectional area when repetitions are performed to failure. Importantly, slow typology individuals performed a significantly higher training volume to obtain similar adaptations compared to fast typology individuals. Muscle typology does not determine the most appropriate resistance training frequency. However, regardless of muscle typology, an additional weekly training (3×/week vs. 2×/week) increases muscle hypertrophy but not maximal dynamic strength. These findings expand on our understanding of the underlying mechanisms for the large inter-individual variability in resistance training adaptations.
在抵抗训练的适应性方面存在相当大的个体间异质性。有人提出，快肌纤维对肥大刺激更为敏感，因此肌肉纤维类型组成的变化是训练反应幅度的一个促成因素。本研究旨在探讨抵抗训练适应性的个体间变异性是否由肌肉类型决定，以及最合适的每周训练频率是否取决于肌肉类型。在力量训练新手中，通过质子磁共振波谱测量肌肉肌肽来选择 11 名慢肌类型（ST）和 10 名快肌类型（FT）个体。参与者以上肢和下肢肌肉在 1RM 的 60%下训练至力竭，其中一只手臂和腿部每周训练 3 次，另一只手臂和腿部每周训练 2 次，持续 10 周。通过 MRI 进行的三维分割评估肌肉体积、最大动态强度（1RM）和纤维类型特异性横截面积（股外侧肌活检）。总的肌肉体积（+3 至+14%）、纤维大小（-19 至+22%）和力量（+17 至+47%）的训练反应显示出相当大的个体间变异性，但这些不能归因于肌肉类型的差异。然而，ST 个体进行了显著更高的训练量以获得这些相似的适应性，而 FT 个体则没有。每周训练 3 次的肢体通常比每周训练 2 次的肢体有更明显的肥大，并且与肌肉类型没有相互作用。总之，当以 60%的 1RM 进行至力竭时，肌肉类型不能解释抵抗训练适应性的高变异性。关键点：本研究调查了肌肉类型（肌肉纤维类型组成）对抵抗训练适应性变异性的影响及其在抵抗训练频率个体化中的作用。我们证明，当重复进行至力竭时，个体的肌肉类型不能解释抵抗训练引起的肌肉体积、最大动态强度和纤维横截面积增加的个体间变异性。重要的是，与 FT 个体相比，慢肌类型个体进行了显著更高的训练量以获得相似的适应性。肌肉类型不能决定最合适的抵抗训练频率。然而，无论肌肉类型如何，每周增加一次训练（每周 3 次与每周 2 次）都会增加肌肉肥大，但不会增加最大动态强度。这些发现扩展了我们对抵抗训练适应性个体间变异性的潜在机制的理解。
