Case Studies in Physiology: Male to female transgender swimmer in college athletics

Abstract

There is current scientific and legal controversy about sports competition eligibility regulations for transgender athletes. In this case study, we quantified performances by an elite, transgender woman (male sex, female gender identity) college swimmer who competed in both the men's and women's NCAA categories. We also contextualized her performances with respect to contemporary elite college swimmers. These data demonstrate that the declines in freestyle swimming performances of a transgender woman after about two years of feminizing gender affirming hormone treatment (0.5% for the 100 to 7.3% for the 1650-yard distance) are smaller than the observed sex-related differences in performance of top athletes (11.4% for the 100 to 9.3% for the 1650-yard distance). Despite slower performances, the transgender woman swimmer experienced improvements in performance for each freestyle event (100 to 1650 yard) relative to sex-specific NCAA rankings, including producing the best swimming time in the NCAA for the 500-yard distance (65th in the men's category in 2018-19 to 1st in the women's, 2022). Similarly, NCAA-ranked male swimmers did not show large improvements in rank in the men's category during the same time frame. Our findings suggest that the performance times of the transgender woman swimmer in the women's NCAA category were outliers for each event distance, including 100-, 200-, 500-, and 1650-yard freestyle events. Our analysis may be useful as a framework for regulators considering participation guidelines which promote fair competition for all athletes- irrespective of gender identity.

The Biological Basis of Sex Differences in Athletic Performance: Consensus Statement for the American College of Sports Medicine

“…Consistent with some retained advantage of performance in transgender women, effects of ~2 yr of GAHT on swimming performance (50–1500 m) in an elite transgender woman (1) resulted in a reduction in performance, but retention of a 5% performance advantage compared with a historical database of competitive times in cisgender women. Because oxygen uptake and muscle power are important predictors of swimming velocity (392), it is plausible that advantages in performance associated with endogenous testosterone were retained.…”

“…This variation in the magnitude of the sex difference in performance across sports and physical tasks is a consequence of the difference in the timing and effects of sex steroid hormones during growth and development and their varying effects on the different biological systems that are most utilized during athletic events (e.g., muscle vs central nervous system). Understanding the latest science for the differences in performance between males and females can inform policies of governing sports and athletic organizations on the inclusion of athletes who are transgender (1,2) and/or have disorders (or differences) of sex development (DSD), also referred to as intersex, within sex-based categories of competition. Thus, we provide definitions of sex and gender (see discussion hereinafter), and a clear picture of the science that dictates those factors that differentiate sexes in athletic performance across different events, as we address the role and inclusion of males and females, men and women in sports, and professions that require physical performance (3,4).…”

The International Olympic Committee framework on fairness, inclusion and nondiscrimination on the basis of gender identity and sex variations does not protect fairness for female athletes

“…This is illustrated by a case study of an American transgender swimmer, who achieved significant National Collegiate Athletic Association (NCAA) ranking improvements (from middle to top) across a range of events after switching from the male to the female category. 65 This occurred as a result of performance decreases that were significantly smaller than male versus female performance differences, supporting the retention of male biological advantage and illustrating the resultant unfairness.…”