Muscle Strength and Power Changes With Gender-Affirming Hormone Therapy.

BACKGROUND

Androgen receptors are highly expressed in upper body muscles, but changes in maximal muscle strength and power in major upper body muscles have not been investigated during gender-affirming hormone therapy (GAHT).

OBJECTIVE

To assess prospective changes in maximal muscle strength and muscle power from before and after 1 year of GAHT.

DESIGN AND

METHODS

Clinical prospective study in 92 transgender persons: 26 transmasculine treatment-naïve (TransM_naïve), 27 transmasculine treatment-ongoing (TransM_ongoing), 29 transfeminine treatment-naïve (TransF_naïve), and 10 transfeminine treatment-ongoing (TransF_ongoing) were examined at baseline and after 1 year of GAHT. Primary outcomes were unilateral upper body maximal muscle strength (kg) and mean and maximal power (watt) measured by low-row dynamic testing. Dual-energy X-ray absorptiometry was conducted in all participants.

RESULTS

In transmasculine persons, the median (quartiles) age was 22 (20; 30) years in TransM_naïve and 26 (22-29) years in TransM_ongoing (median GAHT duration 3 (2; 5) years) at study inclusion. Maximal muscle strength increased 6.3 kg (12%) in TransM_naïve (p ≤ 0.001) and 5.0 kg (7%) in TransM_ongoing (p ≤ 0.001), while maximal muscle power remained unchanged. ∆-muscle strength was positively associated with ∆-lean mass in arms and negatively associated with age at GAHT initiation. In transfeminine persons, the median age was 24 (22; 30) years in TransF_naïve and 40 (31-64) years in TransF_ongoing (median GAHT duration 4 (2; 6) years) at study inclusion. Maximal muscle strength decreased 17.5 kg (23%) in TransF_naïve and -5.0 kg (8%) in TransF_ongoing, which was accompanied by a decrease (23%) in maximal muscle power in TransF_naïve.

CONCLUSION

Upper body muscle strength but not power increased during masculinizing GAHT, whereas muscle strength and power decreased within the first year of feminizing GAHT.