Low body mass to waist ratio is associated with lower muscle mass and muscle strength in school-aged children: a cross-sectional study.

BACKGROUND: Muscle mass and strength influence bone and respiratory health in children, yet measuring muscle mass is costly and time-consuming. The body mass-to-waist ratio (BM/W) is a simple anthropometric parameter that may predict muscle mass. OBJECTIVE: This study examined the relationships between BM/W, muscle and bone mass, handgrip strength (HGS), and pulmonary function in children. METHODS AND PROCEDURES: In this cross-sectional study, 189 children aged 7 to 8 years were analyzed according to sex-specific BM/W quartiles. Differences across quartiles were tested by one-way ANOVA with Bonferroni post-hoc. Multiple regression analyses, stratified by sex and adjusted for height, were performed. Pulmonary function was assessed in a subsample of 133 children. RESULTS: Children in the lowest BM/W quartile showed the lowest muscle (-17%) and bone mass (-25%), HGS (-29%), height-indexed HGS (-21%), FVC (-22%) and FEV1 (-20%) (all P < 0.001), accounting for 73.7% of dynapenia cases. In multivariate models, BM/W was independently associated with muscle mass in both sexes; the association with strength was most robust for height-indexed HGS (P < 0.001), while that with absolute HGS was attenuated after adjusting for height. Pulmonary function was explained by body size, height being the dominant correlate. CONCLUSION: BM/W is positively associated with muscle mass and strength in school-aged children; lowest-quartile children also show lower bone mass and pulmonary function. Low BM/W may indicate the need for early screening and targeted exercise interventions, especially with low handgrip strength, to prevent functional decline.