Waist-to-height ratio identifies children with lower physical activity and reduced cardiorespiratory fitness: Longitudinal evidence from Norwegian primary schools - The Health Oriented Pedagogical Project (HOPP).

OBJECTIVES: Childhood obesity and physical inactivity are major global health concerns because of their links to cardiometabolic risk factors that may persist into adulthood. Waist-to-height ratio (WHtR) has emerged as a practical indicator of central adiposity and metabolic risk. Moderate-to-vigorous physical activity (MVPA) and cardiorespiratory fitness are important factors in reducing obesity-related risk. This study investigated the association between WHtR, physical activity, and fitness in children aged 6-12 years.

METHODS: The Health Oriented Pedagogical Project (HOPP) is a longitudinal cohort study conducted from 2015 to 2020 and including 2297 Norwegian children. WHtR was examined as the main time-varying exposure. Separate linear mixed models were fitted for MVPA, sedentary time, Andersen intermittent running test performance, and VO₂peak as outcomes, with age, sex, and socioeconomic status included as covariates.

RESULTS: Each 0.1 unit increase in WHtR was linked to a -0.62 min/day reduction in average MVPA. Higher WHtR was associated with lower MVPA and lower cardiorespiratory fitness, including both Andersen test performance and VO₂peak. No clear association was observed between WHtR and sedentary time.

CONCLUSION: In this longitudinal cohort, higher WHtR was associated with lower physical activity and lower cardiorespiratory fitness. WHtR may therefore serve as a simple screening indicator for identifying children who may warrant closer assessment of fitness, physical activity, and cardiometabolic risk.