Associations of rope-skipping and endurance running performance with myopia and spherical equivalent refraction in children and adolescents: a cross-sectional study

Objective To examine nonlinear associations and reference thresholds between physical fitness performance and refractive outcomes in children and adolescents. Methods We surveyed 17235 students aged 6–18 years from 35 schools in seven counties or cities in Hainan Province in December 2023. Cycloplegic autorefraction was used, and spherical equivalent refraction averaged between the two eyes (SE _mean ) of ≤−0.50 diopters was classified as myopia. Models adjusted for age, sex, ethnicity, urban–rural residence, near-work duration, outdoor activity time, parental myopia history, BMI, and a centered BMI-squared term, with school-clustered robust standard errors. Waist-to-height ratio was examined in sensitivity analyses. Results The overall myopia prevalence was 64.43%. Among students aged 6–12 years, rope skipping showed a nonlinear association with refractive outcomes, with a reference threshold of 66 skips/min. Below this threshold, each additional 10 skips/min was associated with lower odds of myopia (OR 0.949, 95% CI 0.919–0.980; P=0.001) and a 0.034-D shift toward more hyperopic SE _mean (95% CI 0.016– 0.052; P<0.001). Among students aged 16–18 years, endurance performance showed no clear overall nonlinearity; however, beyond 307 s, each additional 10 s was associated with higher odds of myopia (OR 1.255, 95% CI 1.030–1.531; P=0.025) and a 0.098-D shift toward myopia in SE _mean (95% CI −0.171 to −0.026; P=0.007). Sensitivity estimates were directionally consistent. Conclusions Fitness indicators showed range-specific associations with refractive outcomes. The two thresholds should be regarded as exploratory values for school-level risk stratification rather than causal or diagnostic cutoffs. Missing direct body-composition measures and the cross-sectional design limit interpretation of independent effects.