Hunter, Sandra K.

Sex differences in sports performances continue to attract considerable scientific and public attention, driven in part by high profile cases of: 1) biological male (XY) athletes who seek to compete in the female category after gender transition, and 2) XY athletes with medical syndromes collectively known as disorders or differences of sex development (DSDs). In this perspective, we highlight scientific evidence that informs eligibility criteria and applicable regulations for sex categories in sports. There are profound sex differences in human performance in athletic events determined by strength, speed, power, endurance, and body size such that males outperform females. These sex differences in athletic performance exist before puberty and increase dramatically as puberty progresses. The profound sex differences in sports performance are primarily attributable to the direct and indirect effects of sex-steroid hormones and provide a compelling framework to consider for policy decisions to safeguard fairness and inclusion in sports.

Purpose: While it is well-known that elite males are faster than elite females in all Olympic-length swimming events, less is known about the age of the divergence in swimming performance between the sexes. Thus, this observational study compared swimming performance of elite male and female youths. Methods: We collected the all-time best 100 U.S. freestyle swimming performance times of boys and girls aged 5 to 18 years for six freestyle swimming events from 50m to 1500m. We compared data using univariate ANOVAs and Chi-squared tests. Results: Swimming performance improved with increasing age for both boys and girls (p<0.001) until a plateau— which began at a younger age for girls (15 years) than boys (17 years; sex × age; p<0.001). Before age 8, there was no sex difference in swimming performance (p>0.05). Beginning at age 9 however, boys swimming performance was faster than girls (1.0% to 1.3% depending on distance), and this sex difference in performance increased in magnitude until 18 years (p<0.001; 6.6% to 11.0% depending on distance). While boys represent 50% of the top 100 age-group performances at ages 5 and 6, boys represent an increasingly larger proportion of top performances across years of age including nearly 100% of all top 100 age-group performances beginning at age 15—except for one notable female swimmer in the 1500m Conclusion: Among elite youth swimmers, boys have increasingly faster performances than girls beginning at age 9 years, with minimal sex differences in swimming performance before 9 years. Additionally, boys represent an increasingly larger proportion of the top 100 age-group performances of all-time. No funding. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.