PURPOSE: Currently, total testosterone is the sole eligibility criterion for females in some sporting events. There is a lack of evidence to support these regulations. For this reason, the aim of this study was to investigate the relationship between testosterone and the factors underpinning athletic performance in pre-menopausal females.

METHODS: This project consists of three studies. First, an epidemiological approach was used to assess the relationship between testosterone levels and muscle size and strength in 706 pre-menopausal females using quadratic and linear models. Then, 26 pre-menopausal females underwent a 12-week, tightly controlled resistance training program designed to maximise the muscle anabolic response. Muscle size, strength and power were assessed and muscle biopsies were collected before and after the training program. The steroid profile of blood and urine was measured by gas-chromatography/mass-spectrometry. Muscle fibre size, fibre type distribution and the cellular localisation of the androgen receptor were assessed via immunohistochemistry. Protein expression of the androgen receptor and markers of protein synthesis were measured using Western Blot. Associations between components of the androgen profile and muscle mass and function were assessed via linear models. Finally, primary muscle cell lines were cultured from the participants’ biopsies and treated with testosterone. Protein synthesis rates were assessed via puromycin incorporation. Androgen receptor content and localisation were assessed via Western Blot and immunohistochemistry, respectively.

RESULTS: Total testosterone was not related to lean mass, muscle strength or the adaptation to resistance training when assessed cross-sectionally or longitudinally. Conversely, the free androgen index which is indicative of the amount of bioavailable testosterone was positively related to muscle mass and strength in pre-menopausal females. However, this relationship consistently provided small effect sizes, suggesting that the amount of free testosterone a female has only plays a small role in the regulation of skeletal muscle in females. Finally, testosterone treatment increased myotube diameter in vitro, but it did not influence the total or phospho-protein content of proteins associated with muscle protein synthesis. Instead, testosterone treatment increased the nuclear localisation of the androgen receptor in muscle cells taken from pre-menopausal females. 

CONCLUSIONS: Our data suggest that total testosterone is not a determining factor of muscle mass or strength in pre-menopausal females. Bioavailable testosterone may play a small, yet significant role in the regulation of skeletal muscle. At supra-physiological concentrations, testosterone increases myocyte size. We suggest that this is via genomic signalling of the AR, rather than non-genomic signalling via the mTOR pathway, as previously suggested.

DISCLOSURES: The authors have nothing to disclose.