Nonlinear association between physical fitness and sports injury risk among Chinese high school students: a cross-sectional study

BACKGROUND: Sports injuries are a prevalent public health issue among adolescents, yet the association between physical fitness and injury risk in Chinese high school students remains under-investigated. This study aimed to evaluate the relationship between physical fitness levels and the risk of sports-related injuries among high school students in China. METHODS: A cross-sectional study was conducted among 1,659 students aged 15-18 years from six high schools in Shanghai. Physical fitness was assessed using standardized national tests (e.g., sprint, endurance run, standing long jump, sit-and-reach, strength measures). Sports injury data were collected via validated questionnaires. Students were categorized into quartiles based on composite fitness scores. Multivariate logistic regression models were used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for injury risk across fitness levels. A two-piecewise linear regression was applied to explore potential non-linear associations. RESULTS: The overall injury prevalence was 23.0%, higher in boys (26.7%) than girls (19.2%). Compared to the lowest fitness quartile, students in the highest quartile had a significantly lower injury risk (adjusted OR = 0.13, 95% CI: 0.08-0.17). A clear dose-response relationship was observed (P for trend < 0.001). Below a composite fitness score of 65, each 1-point increase was associated with a 14% reduction in injury odds (OR = 0.86, 95% CI: 0.83-0.89); above this threshold, the association was no longer significant. CONCLUSIONS: Physical fitness was inversely associated with sports injury risk among Chinese high school students. A threshold effect was identified at a fitness score of 65, below which injury risk declined sharply with each point increase. Interventions should prioritize students below this cutoff to effectively reduce injury incidence.