I am a world champion athlete who has published peer reviewed research in this field and I say it is clear that there is male-performance advantage over females.  Men on average are stronger than women due to the relative % of muscle vs. fat, and to power that extra muscle they have more oxygenating cells (haemoglobin) in the blood... ALL of which are controlled by hormones, they are not set at puberty. No-one disputes this. What is less clear is what happens after cross-sex hormone therapy, in trans women in particular. Trans women who compete in female sports are on gender-affirming hormone therapy (GAHT) — typically oestrogen plus medications to lower testosterone. This therapy leads to measurable changes in body composition and function. What the evidence says about performance? After 2 years of GAHT, trans women show little to no advantage over cis women in tests like running 1.5 miles or number of sit-ups. By 1–3 years on GAHT, many performance differences in studied metrics narrow substantially or disappear.
 However, in strength tests (e.g. push-ups, grip strength), some small residual advantage may persist.
 In contrast, some areas suggest worse performance: lung function, efficiency of breathing, and fitness (Braga et al., Saitong et al., and Alvares et al.) when normalised to body size.
 In one study of national-level volleyball players, athletic trans women performed similarly to cis women (but below cis men) across multiple physical metrics.
 In a UK study, athletic trans women (on hormones for 4–6 years) had worse performance in lung function, jump height, and relative VO₂ max (a measure of fitness) than cis women, but absolute grip strength was higher.
 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.
 In short: any advantage that exists is likely to be small, context-specific, and not universal. 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 Fairness and inclusion can coexist. With thoughtful, evidence-based policies, both can be achieved without resorting to blanket bans. transresearch.org.au/post/tr…