Lindsay Briggs

All these female athletes commenting on trans athletes in recent days should have said they don't have a clue what the science says about trans women athletes. 🧵 ~ How HRT changes the body of trans women. Most trans women who compete are on gender-affirming hormone therapy (GAHT) typically oestrogen plus medications to lower T. What the evidence says about performance in trans women athletes. Research has shown worse performance for trans women compared to cisgender women in : lung function, efficiency of breathing, and fitness (Braga et al., Saitong et al., and Alvares et al.) when normalised to body size. Cheung et al. (2023) after 2 years of GAHT, trans women show little to no physical performance advantage over cisgender women. In a UK study, athletic trans women (on hormones for 4–6 years) had worse performance than cisgender women in lung function, jump height, and relative VO₂ max (a measure of fitness) than cis women, but absolute grip strength was higher. In another study of national-level volleyball players, athletic trans women performed similarly to cis women (but below cis men) across multiple physical metrics. And the most comprehensive synthesis to date, a 2026 systematic review and meta-analysis (Sieczkowska et al., British Journal of Sports Medicine) of 52 studies and 6,485 participants, found that trans women on 1–3 years of GAHT had upper-body strength, lower-body strength and relative VO₂ max comparable to cis women, despite higher absolute lean mass. The authors concluded the evidence does not support theories of inherent athletic advantage for trans women over cis women. A 2025 longitudinal study (Harper et al., European Journal of Sport Science) tracked 9 trans women runners and 1 trans woman swimmer before and after starting GAHT. Race times slowed by around 15% in runners (with bigger decrements in longer-distance events) and around 5% in the swimmer. After adjusting for training volume, the runners’ age-graded performance scores did not differ pre- versus post-GAHT, meaning they were roughly as competitive in the women’s category as they had previously been in the men’s category. This is the first study to use both retrospective and prospective data on the same trans women athletes before and after GAHT. Safety concerns. Despite frequent public talk, there is no robust empirical evidence that trans women increase injury risk to cisgender women in sport. Most policies that cite safety are based on theoretical models (assuming trans women are the same as cis men, and comparing cis men to cis women), not on observed injury data. What rules currently exist? Many sporting bodies have eligibility policies. These often require: Maintaining testosterone levels below a threshold (e.g. < 5 nmol/L) for a set duration (e.g. 24 months).� Submission of performance data (times, strength metrics, prior competition data).� Some sports, however, have banned trans women entirely — but these bans tend to lack scientific justification, and they ignore the diversity among trans women in body size, physiology, training history, etc. In summary There is very low participation of trans people in sport due to a large number of barriers such as actual or anticipated discrimination. Hormone therapy leads to substantial physical changes in trans women, which often narrow or eliminate many performance differences over time. Any remaining differences are small and vary by sport. Some studies show a slight residual advantage in certain measures (e.g., handgrip strength) and a disadvantage in others (e.g., lung function and aerobic fitness). How much this matters depends on the demands of the specific sport. Safety concerns are mostly hypothetical. To date, there is no solid evidence that trans women pose a greater injury risk to cis women in sport. Fairness and inclusion can coexist. With thoughtful, evidence-based policies, both can be achieved without resorting to blanket bans. transresearch.org.au/post/tr…