Muscle Androgen Receptor Content but Not Systemic Hormones Is Associated With Resistance Training-Induced Skeletal Muscle Hypertrophy in Healthy, Young Men.
Level 3 - non-randomized controlled study
Prospective non-randomized single-arm cohort study evaluating biomarkers across responder subgroups.
PubMed 30356739 · doi:10.3389/fphys.2018.01373
What was done
Forty-nine resistance-trained young men completed a 12-week resistance exercise training (RET) program. Circulating anabolic hormones (including total and free testosterone, DHEA, DHT, total and free IGF-1, LH, and GH) were measured before and after acute exercise, as well as pre- and post-intervention. Biopsies evaluated intramuscular free testosterone, DHT, 5α-reductase expression, and androgen receptor content in the highest (HIR, n = 10) and lowest (LOR, n = 10) responders. Backward elimination, principal component regression, and subgroup comparisons assessed predictors of changes in lean body mass (LBM) and type 1 and type 2 muscle fiber cross-sectional area (CSA).
What was found
No systemic or intramuscular hormone measured before or after exercise or intervention was consistently selected in regression models or differed between HIR and LOR. The steroidogenic enzyme 5α-reductase increased post-RET in HIR (P < 0.01) but not LOR (P = 0.32). Intramuscular androgen receptor content remained unchanged with RET but was higher at all timepoints in HIR compared to LOR. A significant linear relationship was observed between androgen receptor content and changes in LBM (P < 0.01), type 1 CSA (P < 0.05), and type 2 CSA (P < 0.01) both pre- and post-intervention.
Why it matters
This study demonstrates that intramuscular androgen receptor density, rather than systemic or local hormone levels, associates with resistance training-induced skeletal muscle hypertrophy in trained men.
Limits
The study is limited to healthy, resistance-trained young men. Intramuscular variables were evaluated only in extreme responder subsets (n = 10 per group), and the correlational design cannot determine whether elevated androgen receptor content directly drives hypertrophic responsiveness.
Cited by
- supports Within the physiological normal reference range of testosterone, an individual's baseline testosterone level does not predict their hypertrophic response to resistance training.