Sex Differences in Running Performance Among 8-and-Under and 9-10-Year-Old Children in US Regional Track Championships.

Sex differences in competitive running performance are well documented in adults but understudied in prepubertal children. Prior studies have often focused on elite performers or record holders, potentially neglecting trends across the full competitive field, and some have reported minimal sex-based differences before age 11, leaving the existence of prepubertal performance differences unclear. This study examined whether sex-based differences in running performance are present among all competitors in the 8-and-under and 9-10-year-old age groups at USA Track & Field (USATF) Regional Junior Olympic Championships. All official race times from the 100 m, 200 m, 400 m, 800 m, and 1500 m events were collected from all 15 USATF Regional Championships held in 2022-2024. Preliminary and final race times were compared by sex using two-way ANOVA (p < 0.05), and performance differences were further evaluated across the 95th, 90th, 75th, 50th, 25th, and 10th percentiles. In the 8-and-under group, males (n = 2696 race times) ran 3.8%-5.9% faster than females (n = 2710) across all distances (p < 0.001; Hedges' g = 0.39-0.63). In the 9-10-year-old group, males (n = 3265) ran 3.4%-5.5% faster than females (n = 3182) across all distances (p < 0.001; Hedges' g = 0.31-0.52). The fastest individual males outperformed the fastest individual females by 1.8%-11.6% across events and age groups. Across percentiles, males ran on average 4.4% ± 1.2% faster than females. These findings demonstrate that sex-based differences in running performance are evident by ages 8-10 years and extend across the full spectrum of competitors, not solely elite youth athletes.