Longitudinal trends in physical activity and sedentary behaviour among school children in Norway: The health oriented pedagogical project (HOPP)

Introduction Many children do not achieve recommended levels of physical activity (PA), although PA is important for cardiovascular health, mental well-being, and reducing chronic disease risk. The aim of this study was to describe longitudinal changes in moderate-to-vigorous physical activity (MVPA) and sedentary behavior (SED) during primary school and to examine whether a school-based active learning intervention was associated with attenuated age-related declines in PA. Baseline cross-sectional age gradients are presented as descriptive context and are not interpreted as a causal counterfactual for longitudinal change. Methods The study sample consisted of n = 2123 children (50% females) from the Health Oriented Pedagogical Project (HOPP) in Norway with valid accelerometer data in 2015, aged 6–12 years (mean 9.46 ± 1.75). MVPA and SED were objectively assessed using hip-worn accelerometers based on seven-day averages. Data from 2015–2019 were analyzed using linear and generalized linear mixed-effects models to account for repeated measures and clustering. Results Baseline cross-sectional analyses suggested a decline of 3.5 min·day ⁻ ¹ of MVPA per year of age among children aged 6–12 years. Longitudinally, across five years (2015–2019), MVPA declined on average by 2.2 min·day ⁻ ¹·year ⁻ ¹ (p < 0.001) and SED increased by 6.7 min·day ⁻ ¹·year ⁻ ¹ (p < 0.001). Conclusion Physical activity levels declined, and sedentary behavior increased with age, beginning in early primary school. Over follow-up, the observed longitudinal decline in MVPA and increase in SED were less steep than the baseline cross-sectional age gradients presented for context, but these comparisons should be interpreted descriptively rather than causally.