February 3, 2026

expert reaction to study looking at physical fitness of transgender and cisgender women

A study published in the British Journal of Sports Medicine looks at the body composition and physical fitness of transgender and cisgender women. 

Prof Alun Williams FCASES FTPS, Professor of Sport and Exercise Genomics, Manchester Metropolitan University Institute of Sport, said:

“The authors have been thorough in gathering relevant literature, but the paper suffers from several problems.

“Only longitudinal studies are truly informative, because otherwise we can’t know the contribution of hormonal treatment to fitness nor how much difference in fitness between transgender women and cisgender women existed before treatment began – it might be that transgender women in research studies have self-selected as a group who were not as strong or as aerobically fit as cisgender men before they began treatment.  The longitudinal data (pages 8-9 in the paper) don’t show convincing evidence of changes in physical fitness that remove the advantage known to exist between men and women in the absence of hormonal treatment.  Indeed, other authors (including me) reviewed essentially the same literature and concluded that performance decreases due to hormonal treatment in transgender women were notably smaller than typical differences between men and women, meaning retention of performance advantage (https://doi.org/10.1111/sms.14581).

“Also, as the authors acknowledge, much 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.

“How active people in a study were is a critical factor because we know for certain that training affects physical fitness, so it’s almost worthless to compare groups without tight assessment of training history.

“Strength measurements depend on voluntary effort, and although lab techniques exist that can assess effort, none of the studies reviewed did that.  Therefore, reports of higher muscle mass (unrelated to effort) not leading to higher muscle strength should be treated sceptically.

“Furthermore, hormonal treatment after puberty doesn’t change skeletal dimensions like height, limb length, or shoulder width, so those advantages to men in many sports remain in transgender women regardless of hormone changes.

“Consequently, I don’t agree with the authors that the studies published to date, or their review of them, overturn the evidence for inherent athletic advantage in transgender women.

“I agree with the authors that longitudinal studies with good measurements relevant to sport would help provide more solid evidence on which to base sport policy.”

‘Body composition and physical fitness in transgender versus cisgender individuals: a systematic review with meta-analysis’ by Sofia Mendes Sieczkowska et al. was published in the British Journal of Sports Medicine at 23:30 UK time on Tuesday 3 February 2026. 

DOI: 10.1136/bjsports-2025-110239

Declared interests

Prof Alun Williams: “Research funding received from the International Olympic Committee Medical and Scientific Research Fund; Scientific publications on this topic that reach different conclusions.”