Does body composition mediate the association between moderate-to-vigorous physical activity and physical literacy in school-aged children? A cross-sectional mediation analysis

Background Childhood obesity and physical inactivity are growing global public health concerns. Once predominantly observed in wealthier nations, these issues are now increasingly prevalent in low- and middle-income countries. We aimed to examine the relationship between moderate-to-vigorous physical activity (MVPA) and physical literacy (PL) among children aged 8–12 years, and to determine whether body mass index (BMI) mediates this association. Methods We conducted a cross-sectional study of 1,360 children (8–12 years old, mean age 10.0 ± 1.4 years) from 85 higher secondary schools in South Punjab, Pakistan. Physical activity and PL were assessed using the Canadian Assessment of Physical Literacy (CAPL-2) protocol. Data analyses included descriptive statistics, independent t -tests, chi-square tests, Pearson correlations, and multivariate logistic regression. A regression-based mediation analysis was conducted to examine the mediating role of BMI in the MVPA–PL relationship. Age and sex were included as covariates. Statistical significance was set at p < 0.05 (two-tailed). Results Overall, 79.9% of participants were of normal weight, 9.7% were overweight, and 5.3% were obese. Normal-weight children demonstrated significantly higher average weekly step counts, more MVPA days per week (5.04 ± 1.09 vs. 4.65 ± 1.17), and higher PL scores (53.76 ± 11.72 vs. 45.86 ± 9.87) than overweight or obese children ( p < 0.001 for all comparisons). BMI was negatively associated with PA and PL measures ( r = −0.136 to −0.300, p < 0.01), while MVPA and step count were positively associated with PL ( r = 0.237 to 0.609, p < 0.01). In the mediation analysis, higher MVPA was associated with lower BMI (Path a: β = −0.377, SE = 0.078, p < 0.001), and lower BMI was associated with higher PL (Path b: β = −0.514, SE = 0.065, p < 0.001). MVPA also showed a strong direct association with PL ( c' = 2.091, SE = 0.189, p < 0.001). The indirect effect of MVPA on PL through BMI was statistically significant [β = 0.194, 95% CI (0.107, 0.291)], accounting for approximately 8.5% of the total effect. Sex-stratified analyses indicated that the proportion of the MVPA–PL association mediated through BMI was slightly higher in girls (10.2%) than in boys (7.1%). Conclusion This study provides the first evidence from a Pakistani pediatric population that BMI partially mediates the association between MVPA and physical literacy, though the majority of this relationship remained direct. Children with overweight and obesity demonstrated lower PA participation and reduced PL scores than normal-weight peers, while girls consistently underperformed boys despite comparable BMI and knowledge levels. These findings support the need for culturally relevant, gender-responsive, school-based programmes that promote physical activity while addressing weight-related barriers in under-resourced settings.