Bioavailable testosterone and androgen receptor activation, but not total testosterone, are associated with muscle mass and strength in females.
Level 3 - non-randomized controlled study
Prospective single-arm pre-post cohort study with in vitro mechanistic testing
PubMed 39393048 · doi:10.1113/JP286803
What was done
Twenty-seven untrained pre-menopausal females (mean age 23.5 ± 4.8 years) completed a 12-week resistance training programme. Investigators measured muscle size, strength, power, and plasma and urine androgen levels. Skeletal muscle biopsies were obtained before and after training to quantify androgen receptor (AR) content and nuclear localisation. Primary muscle cells cultured from a subset of participants (n = 6) were treated with testosterone to assess myotube diameter, muscle protein synthesis markers, and AR subcellular localisation.
What was found
The abstract reports directional associations but provides no exact effect sizes, correlation coefficients, or p-values: - Physiological total testosterone was not associated with muscle mass or strength at baseline, nor with changes following resistance training. - Bioavailable testosterone was positively associated with skeletal muscle mass, strength, and training-induced hypertrophy. - In vivo AR nuclear localisation was positively associated with baseline muscle mass and strength, but not with resistance training-induced hypertrophy. - In vitro, supraphysiological testosterone increased myocyte diameter and AR nuclear translocation without activating the Akt/mTOR pathway.
Why it matters
These findings suggest that total circulating testosterone is not an informative marker of muscle mass or training responsiveness in pre-menopausal females, highlighting bioavailable testosterone and intracellular androgen receptor dynamics instead.
Limits
Small sample size (n = 27 overall; n = 6 for cell culture experiments) and lack of a non-training control group. The abstract omits all numerical values, confidence intervals, and p-values. Results are limited to young untrained pre-menopausal females and cannot be generalized to post-menopausal women or athletic populations.