Central Adiposity Versus Body Mass Index in Assessment of Adiposity-Related Differences in Physical Activity Among Schoolchildren Aged 5-12 Years in High-Risk Neighborhoods.

Purpose: Body mass index (BMI) is widely used in childhood obesity surveillance despite limitations in capturing central adiposity, which has been hypothesized to relate to reduced participation in movement. This study compared associations between z-score waist circumference (zWC), z-score waist-to-height ratio (zWHR), and BMI and device-measured physical activity in predominantly African American, low-income schoolchildren. Methods: This cross-sectional study included 264 schoolchildren aged 5-12 years (146 girls, 118 boys; mean age 8.5 ± 1.8 years; ~86% African American; ~93% eligible for free/reduced-price lunch). Anthropometrics and free-living PA (Actigraph GT9X) were measured. Regression models evaluated associations between each anthropometric z-score and PA intensities, adjusting for age, sex, wear time, and school. Results: Measures of central adiposity showed inverse associations with physical activity that were of similar or slightly greater magnitude than those for BMI, although differences between models were modest. All three adiposity measures (zWC, zWHR, zBMI) were significantly and negatively associated with total moderate-vigorous physical activity (MVPA), only in girls. A one-unit increase in zWC was associated with a decrease of 3.334 min/day in MVPA. The largest negative associations were observed for zWC and zWHR with vigorous activity. Conclusions: In this population of schoolchildren, waist-based measures showed inverse associations with physical activity of similar or slightly greater magnitude than BMI, particularly among girls. Although modest differences in model fit prohibit claiming superiority over BMI, these findings support utilizing waist-based measures as practical, low-cost complements to traditional BMI in school-based surveillance and activity targeting.