Background: To explore the cross-sectional relationship between the body mass index (BMI) and physical fitness index (PFI) of Chinese college students. Methods: In total, 30 497 (male 16 197, 55.5%) Chinese college students aged 19-22 were tested for height, weight and five physical fitness indicators (50-m sprint, sit and reach, standing long jump, 1000/800-m run, pull-up/bent-leg situp). Stratified according to age and gender, according to BMI percentile,BMI ≥ 90th Percentile (E), a total of 5 groups, and the PFI composed of 5 indicators of physical fitness was calculated according to age and gender. The comparison of PFI between different BMI groups was carried out using the effect size, and the non-linear relationship between BMI-Z and PFI was analyzed. Results: The relationship between BMI-Z and PFI of male and female college students in China showed an inverted "U"-shaped curve. With comparable BMI, PFI change was greater in males than in females.
Conclusion:The relationship between BMI and PFI of Chinese college students is nonlinear. The physical fitness level of college students who are underweight or overweight and those with obesity is lower than that of normal-weight students.