Key Takeaways
A University of Sao Paulo study suggests trans women may not have a fitness advantage over biological women after hormone therapy, showing comparable physical fitness levels and muscle strength.The study analyzed 50 prior studies and found trans women had similar body fat levels as biological women, with no significant differences in upper or lower body strength and maximal oxygen consumption (VO₂ max).Experts advocate for eligibility criteria in sports rather than blanket bans on trans women, emphasizing the need to focus on improving women’s sports overall.Critics of the study argue the research was poorly designed and that the data used was of low quality, questioning the study’s conclusions.
A new “landmark” study out of the University of Sao Paulo in Brazil “challenges the notion” of banning trans females — aka men — from competing in women’s sporting events.
According to the Independent, the study found “despite larger muscle mass about one to three years after hormone therapy, trans women have physical fitness levels comparable to those” of biological women.
Fifty studies involving a total 6485 people showed trans females had “significantly” more body fat than men — the amount actually was on par with biological women.
And, despite trans females having more muscle mass, “there were no observable differences in upper or lower body strength” between them and real females:
Scientists suspect there could be residual musculoskeletal differences that may not confer an athletic edge.
There was also no observable difference between trans women and [real] women in their maximal oxygen consumption (VO₂ max), a key fitness measure.
In the case of trans men, after one to three years of starting hormone treatment, they had less fat, more muscle, and greater strength.
Citing a key limitation of the research, researchers said studies included in the analysis mainly focused on physiological outcomes, “with little consideration of the social, psychological and cultural factors”, which also shape sport performance.
The concept of “muscle memory”, or the capacity for previous exercise-adapted muscles to retain some advantages even after hormonal alterations, remains unexplored, according to scientists.
The researchers concluded that “convergence of transgender women’s functional performance with cisgender women […] challenges assumptions about inherent athletic advantages.”
According to the Independent report, endocrinologist Ada Cheung who runs the Trans Health Research Group at the University of Melbourne said “blanket bans on transgender women in sport are not supported by the best available evidence.”
Ada Cheung / U. Melbourne
She added “Instead of blanket bans, we need eligibility criteria for elite sport, and we should focus on the real work of supporting women’s sport: improving visibility and pay, reducing sexual harassment and assault, expanding access to facilities and coaching, and ensuring fair media coverage.”
The Trans Health Research Group’s “Key Definitions” page includes terms such as “brotherboy” and “sistergirl” (Aboriginal words describing “gender diverse people who have a male/female spirit and take on men’s/women’s roles within the community”), and its site notes a September 2025 article claiming hormone therapy “often narrow[s] or eliminate[s] many performance differences over time” (between trans and biological women).
The piece (which begins with the trigger warning “contains reference to exclusion of, and discrimination against, trans people in sport”) says bans against trans females in women’s sports “tend to lack scientific justification, and […] ignore the diversity among trans women in body size, physiology, training history, etc.”
The University of Manchester’s Emma Hilton, a developmental biologist, chided the Brazilian study as “an insane bunch of cherry-picked metrics, cobbled together to try and argue that trans-identifying males should be in female sport.”
What an insane bunch of cherry-picked metrics, cobbled together to try and argue that trans-identifying males should be in female sport. https://t.co/5VVqzsw8mK
— Emma Hilton (@FondOfBeetles) February 4, 2026
Manchester Metropolitan University’s Alun Williams, a professor of Sport and Exercise Genomics, also took issue with the study: “[M]uch of the data they reviewed was low quality due to poor study design or measurement techniques, and little control of confounding factors like how much exercise people did.”
MORE: King’s College London rejects research on trans athletes for calling men ‘males’
MORE: U. Washington professor: ‘no scientific answer as to what is fair’ re: trans-female athletes
