Association between college students 'physical fitness index and negative emotional symptoms: an empirical study based on college students in Chongqing City, China.

Objectives: To investigate the independent associations between the physical fitness index (PFI), as well as individual physical fitness metrics, and negative emotional symptoms (stress, anxiety, and depression) among college students; and to analyze gender-specific variations in these associations, thereby providing empirical, fitness-based evidence for mental health interventions in higher education institutions. Methods: Utilizing a cross-sectional design, this study selected 2,190 college students from 73 universities across Chongqing via stratified cluster sampling. A standardized physical fitness test battery-comprising vital capacity, the 50-meter sprint, the 800/1000-meter run, the sit-and-reach test, and pull-ups/sit-ups-was administered to calculate the comprehensive PFI. Negative emotional symptoms were assessed using the 21-item Depression Anxiety Stress Scales (DASS-21). Multivariable Logistic regression models were employed to evaluate the independent associations between physical fitness and negative emotional symptoms, after comprehensively adjusting for moderate-to-vigorous physical activity (MVPA), muscle-strengthening exercise (MSE), screen time, sedentary duration, and sociodemographic variables. Results: The detection rates of stress, anxiety, and depression symptoms were 68.08%, 67.67%, and 12.37%, respectively. In conventional categorical models, moderate and high PFI were associated with lower odds of all three outcomes in the pooled sample, although several high-PFI estimates were extremely small. Firth sensitivity analyses supported inverse associations for high PFI across outcomes and sexes; however, moderate PFI was not statistically associated with stress in female students or anxiety in male students. Continuous PFI analyses showed lower odds of each outcome per 1-SD increase in the pooled and sex-stratified samples (all Conclusions: Higher PFI was independently associated with lower odds of negative emotional symptoms among college students. The consistency of direction across categorical, Firth-penalized, and continuous-PFI models supports the robustness of the association, but the extreme categorical estimates, model-calibration findings, sample-relative cutoffs, and cross-sectional design require cautious interpretation. Longitudinal and intervention studies are needed before PFI is used as a clinical or campus screening threshold.