Abstract
The physical advantages in elite power sports that allow men to surpass women are derived from the experience of male puberty. By creating testicular testosterone production 20-30-fold over women at any age, sustained exposure over years to adult male testosterone concentrations produces larger and stronger muscles, bones, and the cardiorespiratory system with a higher blood hemoglobin explaining those advantages. While genetic advantages in exercise performance unrelated to sex are accepted in elite sports, adults who have experienced male puberty but have female gender identity, such as male-to-female transgender or intersex (XY Disorders of Sexual Development, DSD), create a category-defeating conflict if they compete in female power sports. Transgender women seek feminization using estrogen treatment, which can suppress postpubertal endogenous testosterone but even sustained complete testosterone suppression leaves an unfair legacy of physical advantages. By contrast, XY DSDs do not seek hormonal feminization and recognize that testosterone suppression impedes their performance. Hence, understanding the biology of male-bodied athletes with female gender identity is crucial to effective management, which is geared toward maintaining fairness and safety for typical women competing in elite female events. Such sex-based restrictions are not required in recreational, junior, or nonprofessional sports or where physical advantages are not operative. After the IOC's controversial 2021 Framework document, a growing consensus among major international sports federations is establishing a working definition of male and female sports sex to facilitate fairness and safety in elite sports, which depend on power, strength, speed, or endurance.