Trans women don’t have enough testosterone to ruin women’s sports
Executive summary
Scientific literature shows that lowering circulating testosterone in trans women through gender-affirming hormone therapy reduces hemoglobin, muscle mass and strength and often brings serum testosterone into the typical female range within months, but several longitudinal and cross-sectional studies report that post‑pubertal trans women can retain measurable athletic advantages—sometimes persisting beyond 12 months—that are likely to matter at elite margins of competition [1] [2] [3] [4]. Sports scientists and policy makers therefore disagree: some argue one year of suppression is sufficient for inclusion, others point to evidence of retained advantages and urge longer or sport-specific rules [5] [3] [6].
1. What the core claim really means: “ruin” is about margins, not absolutes
The fear that trans women will “ruin” women’s sports presumes a systemic, decisive advantage; in elite sport the relevant question is whether remaining advantages exceed the tiny performance margins—often 1–2%—that separate winners from the rest, and multiple reviews warn that even small residual differences in strength, hemoglobin, or body dimensions can matter in high‑level competition [7] [8] [1].
2. What hormones do, and what suppression achieves
Testosterone during and after male puberty drives increases in muscle mass, hemoglobin and bone structure; starting gender‑affirming hormone therapy (GAHT) typically reduces total testosterone, decreases lean mass and hemoglobin, and lowers strength over months to years, with many clinical reports showing significant declines by 12 months [9] [2] [1].
3. Evidence that advantages often persist
Several peer‑reviewed studies and systematic reviews conclude that despite testosterone suppression trans women who transitioned after puberty frequently retain performance advantages—some studies report persistent differences in strength or running performance after one or two years, and a 2020–2021 body of work prompted calls for policies longer than a single year for elite competition [3] [6] [4].
4. Evidence that suppression can eliminate measurable edge in some contexts
Other researchers, including longitudinal investigators cited by the IOC, find that prior exposure to male‑range testosterone does not necessarily confer an enduring advantage across every performance metric and that many trans women reach female norms for circulating testosterone and for some functional measures after treatment, supporting inclusion at various levels of sport [5] [10] [11].
5. The middle ground — sport, event and level matter
Experts emphasize heterogeneity by sport: attributes fixed by puberty such as height, limb length and hand size cannot be reversed and may advantage trans women in sports where those traits are decisive (basketball, volleyball), whereas in other events the declines in hemoglobin and muscle after GAHT may largely erase differences—thus scientific advice increasingly favors sport‑ and event‑specific policies rather than one universal rule [12] [8] [2].
6. Policy, values and unresolved science
Governing bodies balance fairness and inclusion amid imperfect science: the IOC, World Athletics and national federations have shifted rules over time toward testosterone thresholds and durations, but disagreement persists because studies differ in size, methods, and athlete training status, and because stakeholders have competing agendas—protecting female competition, promoting inclusion, and managing public perception—which means science alone will not end the debate [4] [13] [14].