If young men lift weights for 15 weeks, their arm muscles get bigger—about 10–12% for the whole muscle and 9–24% for the individual muscle fibers—no matter if their body’s hormone levels spike during workouts or stay normal.

A randomized controlled trial with young male participants assigned to either a 15-week resistance training program or a non-exercising control group, with muscle cross-sectional area measured via MRI or ultrasound at baseline and post-intervention, and acute systemic anabolic hormone levels (e.g., testosterone, growth hormone) monitored before and after each session to stratify analysis by hormone response (elevated vs. baseline-maintained).

A longitudinal cohort study tracking young men undergoing 15 weeks of standardized resistance training, with serial measurements of muscle cross-sectional area and acute post-exercise anabolic hormone levels at multiple time points to determine if changes in muscle size occur independently of hormone fluctuations.

A case-control study comparing young men who achieved high muscle growth (top quartile) vs. low growth (bottom quartile) after 15 weeks of resistance training, matched for training volume and diet, to assess whether differences in acute anabolic hormone responses explain the variation in outcomes.

A meta-analysis pooling data from published RCTs of resistance training in young men, extracting outcomes for elbow flexor and muscle fiber CSA changes, and stratifying results by whether acute anabolic hormone levels were measured and whether they were elevated or maintained during training.

An animal study using young male rodents subjected to resistance training (e.g., ladder climbing with load) for 15 weeks, with experimental manipulation of systemic anabolic hormones (e.g., via implants or inhibitors) to test whether muscle growth occurs independently of hormone levels.