Transgender Athlete Competitive Performance and Eligibility Outcomes

What the evidence says

Testosterone suppression during gender-affirming hormone therapy (GAHT) produces measurable declines in transgender women's physiological and athletic performance, but the rate and completeness of those declines differ by measure. Hematological markers move fastest: hemoglobin and hematocrit decline 11–14% and reach the cisgender-female range within three to four months of GAHT. Muscle-related measures move slower and less completely: lean body mass falls approximately 5% at 12 months, handgrip strength falls 7–9% over 12–24 months (7–13% in a separate longitudinal sample), and countermovement jump falls 23–29% after one year — yet muscle cross-sectional area and strength can remain elevated beyond 36 months of treatment, and testosterone suppression does not reverse muscle size in transgender women to female levels.

Even where declines are sizable, some comparative advantage over cisgender women persists in specific measures: transgender women's handgrip strength remained 17% above baseline transgender-men levels post-suppression, sitting at approximately the 25th percentile for males but above the 90th percentile for females both before and after hormone treatment. Pushup and sit-up performance, by contrast, declined to levels approaching cisgender women. Running performance shows the same pattern of partial, not complete, convergence: a relative advantage in 1.5-mile running performance remained evident after two years of GAHT even as strength measures normalized, while separate longitudinal data (U.S. Air Force personnel) found physical performance declined by as much as 31% over the same two-year window. Declines were generally larger in longer-duration endurance events than in shorter events.

Statistical adjustment changes the picture: differences between transgender and cisgender athletes were largely attenuated after controlling for body mass and other anthropometric variables, and transgender men and women performed more similarly to their respective cisgender counterparts once body size and composition were accounted for — though transgender men in that comparison performed as relatively smaller men, indicating a residual size difference rather than full elimination.

Two boundary findings frame the magnitude at stake. First, the baseline male-female performance gap before any hormone intervention is itself 10–50% depending on sport, emerging at puberty and most pronounced in sports relying on muscle mass and explosive upper-body strength. Second, transgender men show the mirror-image process: testosterone rises into the cisgender male range and muscle mass rises into the range of untreated transgender women within one year of cross-sex hormone treatment, with one analysis concluding transgender men are likely able to compete without an athletic advantage after one year, while a comparable level of certainty was not reached for transgender women given their larger retained muscle mass.

Evidence on regulatory and elite-competition contexts is thinner. Specific testosterone-based eligibility regulations (the IAAF hyperandrogenism regulations) were found to lack robust, peer-reviewed evidence of a consistent performance advantage linked to endogenous testosterone, and the Court of Arbitration for Sport suspended those regulations in 2015 for insufficient scientific justification. Separately, systematic-review-level assessments conclude there is no direct or consistent research demonstrating an athletic advantage at any stage of transgender transition, and that the absence of direct, consistent physiological performance data — particularly at elite competitive levels — prevents a consensus determination. This last point is a direct absence in the record: none of the sources here supply elite-athlete performance data; the underlying measurements are drawn from non-elite, military, or small clinical samples.

Where the evidence splits

The clearest split is between studies reporting quantified, persistent advantages in transgender women after testosterone suppression and systematic reviews concluding no such advantage is established. Hilton (2020) and Chiu (2026) report a retained 17% grip-strength advantage, muscle cross-sectional area and strength elevated beyond 36 months, and a 1.5-mile running advantage after two years. Jones (2016) and Chan (2024), by contrast, conclude there is "no direct or consistent research" demonstrating an athletic advantage at any stage of transition, and that the athletic advantage attributed to transgender women rests on "indirect and inconclusive evidence." The sources do not reconcile this directly, but the citations themselves show a temporal gap: Jones (2016) is the earliest of the group, predating the longitudinal studies (Harper et al., Hamilton et al.) that Hilton (2020) and Chiu (2026) later synthesize — so the later, more specific quantified findings were not available to the earlier systematic review.

A second split concerns running performance in a specific small, self-reported sample of transgender women runners. One source (Atherton, 2025, citing a retrospective study of 8 non-elite transgender female runners) reports "statistically similar self-reported running times before and after their transitions" — no measured effect. Another (Jones, 2016), describing a comparably sized self-reported sample (N=8), reports running times "significantly slower" post-testosterone-suppression than pre-suppression. Both sources flag the small sample size and self-report method as limitations, but neither explains why the two characterizations of similarly sized samples diverge; the split is unexplained by the sources on this page.

Thresholds and dose-response

Hemoglobin and hematocrit decline to the cisgender-female range within three to four months of GAHT, while lean body mass, muscle cross-sectional area, and strength often remain higher than cisgender-women levels even after 36 months — a threshold showing hematological and muscular adaptations resolve on markedly different timelines. Testosterone in transgender men rises to the cisgender male range within one year of cross-sex hormone treatment, at which point muscle mass has risen into the range of untreated transgender women; testosterone in transgender women falls to castration levels within the same one-year window. Grip strength in transgender women declines with duration of suppression: 7% at 12 months versus 9% at 24 months, a larger reduction at the longer duration. Countermovement jump fell 23–29% after one year of testosterone suppression. Athletic performance declines were generally larger in longer-duration endurance events than in shorter events, though no specific percentage was attached to that gradient. The male-female performance gap of 10–50% is itself conditional on sport type, being more pronounced in sports relying on muscle mass and explosive upper-body strength.

Open empirical questions

• Whether the retained advantages found in non-elite and military samples (17% grip strength, elevated muscle cross-sectional area beyond 36 months, 1.5-mile running advantage at 2 years) replicate in elite competitive athletes — none of the sources here supply elite-level data.
• Whether the muscle mass/strength gap eventually closes with follow-up longer than 36 months, or plateaus at a persistent residual level.
• Whether proposed "muscle memory" mechanisms (myonuclei permanence, epigenetic changes) that might explain persistence of male-puberty adaptations after suppression are real in transgender populations — no source here directly measures them.
• Whether the "no advantage" conclusion reached for transgender men after one year generalizes across sports, competitive levels, and regulatory contexts beyond the studies sampled.