Muscle strength changes and physical activity during gender-affirming hormone therapy: A systematic review

Higher muscle strength is associated with improved overall health and lower mortality. Muscle strength changes during gender-affirming hormone therapy is possibly linked to gender-affirming hormone therapy modality, age at initiation, gender-affirming hormone therapy duration, and physical activity.

To review published literature on muscle strength changes during gender-affirming hormone therapy.

Studies were included if they met the PICOS criteria; P: transgender individuals ≥18 years, I: gender-affirming hormone therapy, C: gender-affirming hormone therapy-naïve transgender persons or cisgender controls, O: muscle strength and physical activity in relation to muscle strength, S: prospective cohorts or cross-sectional.

Fifteen studies with data on 1206 transgender persons (722 transmasculine persons, median age 23-37 years and 484 transfeminine persons, median age 27-41 years) were included. Prospective design was used in eight out of 15 studies (two out of eight on transmasculine, two out of eight on transfeminine, and four out of eight on both) and seven out of 15 were cross-sectional (two out of seven on transmasculine, four out of seven on transfeminine, and one out of seven on both). Isometric elbow flexion/extension, lower body strength, and handgrip strength were assessed in one out of 15 studies, four out of 15, and 12 out of 15 studies, respectively. Bias rating was moderate to high.

Masculinizing gender-affirming hormone therapy resulted in increased (four out of six studies) or unchanged (two out of six studies) muscle strength, while feminizing gender-affirming hormone therapy resulted in decreased (three out of six studies) or unchanged (three out of six studies) muscle strength. Muscle strength changes mainly occurred during the first year after initiating gender-affirming hormone therapy and age at initiation had no impact.

Transmasculine and transfeminine persons had higher strength compared with cisgender women, but lower strength than cisgender men. Physical activity was unchanged during gender-affirming hormone therapy in five out of prospective studies, while transfeminine persons were less physically active than cisgender men in five out of five prospective studies.

Muscle strength appeared to increase during masculinizing gender-affirming hormone therapy and decrease during feminizing gender-affirming hormone therapy, whereas physical activity was unchanged. Given high risk of bias, more research is necessary. Improving transgender care requires engagement of transgender persons in physical activity.