Anthropometric Adiposity Indicators and Handgrip Strength Relative to Body Size in Schoolchildren Aged 6–10 Years from Valparaíso, Chile: A Cross-Sectional Study

Background/Objectives: Absolute handgrip strength (HGS) increases with body size, which complicates its interpretation in children with excess adiposity. We examined the associations between anthropometric adiposity indicators and HGS in children aged 6–10 years, accounting for age, sex and body size. Methods: In this cross-sectional study, 163 schoolchildren (86 girls; 8.5 ± 1.2 years) from two public schools in Valparaíso, Chile, were analyzed. Body fat percentage (%BF), waist-to-height ratio (WHtR), BMI z-score and HGS were measured. Regression models of absolute HGS were adjusted for age, sex and height. The HGS-to-BMI ratio (HGS/BMI), previously termed “muscle quality index”, was analyzed exploratorily. Results: After adjustment for age, sex and height, no adiposity indicator was associated with absolute HGS (%BF: B = −0.05 kg per 1%, 95% CI −0.12 to 0.02; all p ≥ 0.15), consistently across sensitivity analyses. Higher %BF (β = −0.34) and WHtR (β = −0.24) were associated with lower HGS/BMI (both p < 0.001). Conclusions: Children with higher adiposity were not stronger in absolute terms than peers of the same age, sex and height; therefore, their strength relative to BMI was lower. This inverse association reflects the ratio’s denominator and should not be interpreted as poorer muscle quality or metabolic health. It should be noted that HGS/BMI is an exploratory indicator of relative strength, not a measure of muscle quality or a metabolic marker.