Defining sex in the sporting world.

At an elite international level, professional sports have a well-established fairness-based binary sex classification which is challenged by male-bodied athletes with female gender identity, notably male-to-female transgender and XY Disorders of Sex Development (DSD) individuals seeking to compete in female events. For sports where success depends on power and/or endurance, physical advantages stemming from male puberty, which produces men's circulating testosterone concentrations 20-30 times those of children or women at any age, leading to larger and stronger muscles, bones, cardiorespiratory functions and blood hemoglobin. Yet complete suppression of endogenous testosterone after male puberty leaves a legacy of reduced but not eliminated physical advantages. Hence a protected female category in power sports is essential to allow women a fair and safe chance at the fame and fortune derived from success. For community, recreational and youth sports, or those without male physical advantages invoking safety or fairness issues, inclusivity may prevail.