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<p>While the role of resistance training-induced muscle hypertrophy on early strength gains is still debated, it is unclear whether the specificity of training, such as high-load (H) training for increasing strength, results in different motor unit (MU) adaptations than combined high- and low-load (H + L) training for increasing strength and hypertrophy. Therefore, this study examined the effects of six weeks of either H− or H + L-training on leg press 1-repetition maximum (1-RM), isometric knee extensor strength via maximal voluntary contraction (MVC), and muscle cross-sectional area (mCSA) and MU behavior of the vastus lateralis (VL) in untrained males that were pseudorandomized into a H (n = 18), H + L (n = 17), or a control group (n = 11). Surface electromyographic (sEMG) signals for a 40% MVC were recorded from the VL and decomposed for analysis of MU: recruitment thresholds (RTs), action potential amplitudes (MUAP<sub>AMPs</sub>), and mean firing rates (MFRs). Normalized EMG amplitude (N-EMG<sub>RMS</sub>) at 40% MVC was also calculated. Despite a 21% increase in mCSA for H + L compared to 4% for H, both training groups had similar increases for 1-RM and MVC. Additionally, H + L exhibited hypertrophied muscle fibers for MUs with RTs ≥ 20% MVC, decreased MFR of those MUs, and lower N-EMG<sub>RMS</sub> at 40% MVC, whereas H increased MFRs of the lower-threshold MUs with no change in MU size or N-EMG<sub>RMS</sub>. The findings of this study provide support that early changes in MU behavior are sensitive to specificity of training and/or changes in muscle morphology, whereas early strength gains are not necessarily driven by increases in mCSA.</p>

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Differential motor unit firing rate and hypertrophic adaptations of the vastus lateralis despite similar strength increases following high-load versus combined high- and low-load resistance training interventions

  • 期刊论文

  • 发表日期：

    2026年6月21日

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  • Alex A. Olmos,
  • Daniel J. Lawson,
  • Stephanie A. Sontag,
  • Lyric D. Richardson,
  • Brenden L. Roth,
  • Sunggun Jeon,
  • Allen L. Redinger,
  • Sean M. Gamache,
  • Michael A. Trevino

摘要

While the role of resistance training-induced muscle hypertrophy on early strength gains is still debated, it is unclear whether the specificity of training, such as high-load (H) training for increasing strength, results in different motor unit (MU) adaptations than combined high- and low-load (H + L) training for increasing strength and hypertrophy. Therefore, this study examined the effects of six weeks of either H− or H + L-training on leg press 1-repetition maximum (1-RM), isometric knee extensor strength via maximal voluntary contraction (MVC), and muscle cross-sectional area (mCSA) and MU behavior of the vastus lateralis (VL) in untrained males that were pseudorandomized into a H (n = 18), H + L (n = 17), or a control group (n = 11). Surface electromyographic (sEMG) signals for a 40% MVC were recorded from the VL and decomposed for analysis of MU: recruitment thresholds (RTs), action potential amplitudes (MUAPAMPs), and mean firing rates (MFRs). Normalized EMG amplitude (N-EMGRMS) at 40% MVC was also calculated. Despite a 21% increase in mCSA for H + L compared to 4% for H, both training groups had similar increases for 1-RM and MVC. Additionally, H + L exhibited hypertrophied muscle fibers for MUs with RTs ≥ 20% MVC, decreased MFR of those MUs, and lower N-EMGRMS at 40% MVC, whereas H increased MFRs of the lower-threshold MUs with no change in MU size or N-EMGRMS. The findings of this study provide support that early changes in MU behavior are sensitive to specificity of training and/or changes in muscle morphology, whereas early strength gains are not necessarily driven by increases in mCSA.