Objective:

To investigate the associations between BMI and physical fitness indicators among primary school students in Sichuan Province, focusing on differences by gender, ethnicity, and age.

Approach:

• Study Design: Analyzed physical fitness data from 36,092 primary school students aged 7–12 using multivariate analysis of variance, correlation analysis, and hierarchical multiple regression analysis.

Key Findings:

• Significant differences in BMI were found across ethnicities, genders, and age groups (p < 0.001).
• Han students had a higher average BMI (17.07) compared to Yi students (16.90) (F = 31.942, p < 0.001).
• Boys had a higher average BMI (17.18) than girls (16.85) (F = 131.733, p < 0.001).
• BMI increased significantly with age, peaking in the 12-year-old group (M = 18.08).
• BMI was negatively correlated with 50-meter run performance (r = −0.266, p < 0.01) and lung capacity (r = −0.186, p < 0.01).
• The final model explained only a modest proportion of BMI variance (R2 = 0.110).

Interpretation:

BMI in primary school students was significantly associated with gender, ethnicity, age, and physical fitness indicators.

Limitations:

• Several potential confounders, including diet, socioeconomic status, physical activity, and sleep, were not included in the adjusted models, which may limit the interpretation of the findings.
• The effect sizes observed were generally small.

Conclusion:

The study provides context-specific evidence on the associations between BMI and physical fitness among primary school students in Sichuan Province.