Muscular and systemic correlates of resistance training-induced muscle hypertrophy

PLoS One. 2013 Oct 9;8(10):e78636. doi: 10.1371/journal.pone.0078636. eCollection 2013.


Purpose: To determine relationships between post-exercise changes in systemic [testosterone, growth hormone (GH), insulin like grow factor 1 (IGF-1) and interleukin 6 (IL-6)], or intramuscular [skeletal muscle androgen receptor (AR) protein content and p70S6K phosphorylation status] factors in a moderately-sized cohort of young men exhibiting divergent resistance training-mediated muscle hypertrophy.

Methods: Twenty three adult males completed 4 sessions•wk⁻¹ of resistance training for 16 wk. Muscle biopsies were obtained before and after the training period and acutely 1 and 5 h after the first training session. Serum hormones and cytokines were measured immediately, 15, 30 and 60 minutes following the first and last training sessions of the study.

Results: Mean fiber area increased by 20% (range: -7 to 80%; P<0.001). Protein content of the AR was unchanged with training (fold change = 1.17 ± 0.61; P=0.19); however, there was a significant correlation between the changes in AR content and fiber area (r=0.60, P=0.023). Phosphorylation of p70S6K was elevated 5 hours following exercise, which was correlated with gains in mean fiber area (r=0.54, P=0.007). There was no relationship between the magnitude of the pre- or post-training exercise-induced changes in free testosterone, GH, or IGF-1 concentration and muscle fiber hypertrophy; however, the magnitude of the post exercise IL-6 response was correlated with muscle hypertrophy (r=0.48, P=0.019).

Conclusion: Post-exercise increases in circulating hormones are not related to hypertrophy following training. Exercise-induced changes in IL-6 correlated with hypertrophy, but the mechanism for the role of IL-6 in hypertrophy is not known. Acute increases, in p70S6K phosphorylation and changes in muscle AR protein content correlated with muscle hypertrophy implicating intramuscular rather than systemic processes in mediating hypertrophy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Cohort Studies
  • Growth Hormone / blood
  • Hormones / blood
  • Humans
  • Hypertrophy / blood
  • Hypertrophy / etiology
  • Hypertrophy / pathology
  • Insulin-Like Growth Factor I / analysis
  • Interleukin-6 / blood
  • Male
  • Muscle, Skeletal / metabolism
  • Muscle, Skeletal / pathology*
  • Phosphorylation
  • Receptors, Androgen / analysis
  • Receptors, Androgen / metabolism
  • Resistance Training / adverse effects*
  • Ribosomal Protein S6 Kinases, 70-kDa / metabolism
  • Testosterone / blood
  • Weight Lifting
  • Young Adult


  • AR protein, human
  • Hormones
  • Interleukin-6
  • Receptors, Androgen
  • Testosterone
  • Insulin-Like Growth Factor I
  • Growth Hormone
  • Ribosomal Protein S6 Kinases, 70-kDa

Grant support

This work was supported by a grant from the Natural Sciences and Engineering Research Council of Canada to SMP. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.