Associations between adiposity indicators and composite motor fitness among boys and girls in late childhood

Abstract

Adiposity is associated with physical and motor fitness in children, but the relative contribution of different body-composition and adiposity indicators to overall motor fitness remains unclear. This study examined the associations of body mass index (BMI), body fat percentage (BF%), fat mass (FM), muscle mass (MM), and waist-to-height ratio (WHtR) with a composite motor fitness index (MOTOFIT) in younger school-age children. A cross-sectional study was conducted in 306 children (163 girls and 143 boys; mean age 9.89 ± 0.60 years). Body composition was assessed using bioelectrical impedance analysis. Motor fitness was evaluated using hand tapping, standing long jump, sit-ups, and the 10 × 5 m shuttle run. Standardized Z-scores from the four tests were combined into MOTOFIT. Associations were examined using Pearson correlations and separate hierarchical multiple regression models adjusted for age and sex, while differences across adiposity-status groups were analyzed using ANCOVA. BF% showed the strongest negative association with MOTOFIT ( r  = −0.252, p  < 0.001), followed by WHtR ( r  = −0.209, p  < 0.001), FM ( r  = −0.205, p  < 0.001), and BMI ( r  = −0.170, p  = 0.003), whereas MM was not significantly associated with MOTOFIT ( r  = −0.009, p  = 0.875). After adjustment for age and sex, BF% provided the largest incremental contribution to the explained variance in MOTOFIT ( Δ R 2  = 0.057), followed by WHtR ( Δ R 2  = 0.051), FM ( Δ R 2  = 0.042), and BMI ( Δ R 2  = 0.037), whereas MM did not significantly contribute to the model. Adiposity status was significantly associated with MOTOFIT ( F (2,301) = 11.764, p  < 0.001, η p 2  = 0.072). Children in the normal body fat group had higher adjusted MOTOFIT values than children with elevated body fat ( p  = 0.004) and those with obesity ( p  < 0.001). Higher adiposity was associated with lower overall motor fitness in late childhood. BF% and WHtR provided greater incremental information on MOTOFIT than BMI, whereas MM did not independently contribute to the model. These findings support the complementary assessment of total and central adiposity alongside multidimensional motor fitness when evaluating physical development in children.