A landmark review of studies suggests that transgender women may not retain a fitness advantage in women's sport after hormone therapy. The analysis, led by Brazilian scientists, challenges claims that trans athletes have inherent advantages due to biological differences.
The researchers examined around 50 studies involving 6,485 people, including 2,943 trans women, 2,309 trans men, 568 cisgender women and 665 cisgender men aged 14 to 41. They found that after one to three years of gender-affirming hormone therapy, trans women's body composition differed from both cis men and cis women, with fat levels similar to cis women.
Although trans women had greater muscle mass, the study found no significant differences in upper or lower body strength compared with cis women. There was also no observable difference in maximal oxygen consumption (VO₂ max), a key measure of aerobic fitness.
Scientists noted that residual musculoskeletal differences may not confer an athletic edge. However, they highlighted limitations, including a lack of data on social, psychological and cultural factors, and the unexplored concept of 'muscle memory'. They called for future long-term studies focusing on performance-specific metrics.
Experts not involved in the study urged caution. Kim Meredith-Jones from the University of Otago said the results cannot be applied to young people using puberty blockers or transitioning in adolescence. Endocrinologist Ada Cheung from the University of Melbourne stated that blanket bans on trans women in sport are not supported by the best available evidence, and that fairness and inclusion can coexist.
