Elevations in ostensibly anabolic hormones with resistance exercise enhance neither training-induced muscle hypertrophy nor strength of the elbow flexors.
Level 2 - randomized trial
Within-subject controlled experimental trial in humans
PubMed 19910330 · doi:10.1152/japplphysiol.01147.2009
What was done
Twelve healthy young men (mean age 21.8 ± 1.2 yr, BMI 23.1 ± 0.6 kg/m²) trained their elbow flexors independently for 15 weeks on separate days under two distinct hormonal conditions. In the low hormone (LH) condition, participants performed isolated arm curls to maintain basal hormone concentrations. In the high hormone (HH) condition, participants performed identical arm exercises followed immediately by a high volume of leg resistance exercise to elicit increases in endogenous hormones. Serum growth hormone, IGF-1, and testosterone were assessed, along with elbow flexor muscle cross-sectional area (CSA), fiber CSA (type I and II), and strength.
What was found
The HH protocol induced significant elevations (P < 0.001) in serum GH, IGF-1, and testosterone immediately and at 15 and 30 min post-exercise, whereas the LH protocol produced no elevation; this divergent response persisted late into the training period. Muscle CSA increased by 12% in LH and 10% in HH (training effect P < 0.001) with no difference between conditions (condition × training interaction, P = 0.25). Type I (P < 0.01) and type II (P < 0.001) muscle fiber CSA increased with training without any additional effect from the HH condition. Strength gains in the elbow flexors did not differ between the LH and HH conditions.
Why it matters
This study shows that transient, exercise-induced spikes in systemic endogenous anabolic hormones do not augment resistance training-induced muscle hypertrophy or strength, indicating that local intramuscular mechanisms drive these adaptations.
Limits
The sample size was very small (n = 12) and limited to young, healthy males. The abstract does not provide exact strength gain numbers, dietary control details, or participant training history, and the findings in elbow flexors may not necessarily generalize to all other muscle groups or populations.
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