Why are children different in their moderate-to-vigorous physical activity levels? A multilevel analysis.

Objective: Children's differences in moderate-to-vigorous physical activity levels are not at random. This study investigates the relevance of individual- and school-level characteristics in explaining these differences.

Methods: In total, 307 children (154 girls) aged 5-10 years, from 19 Portuguese schools, were sampled. Height and weight were measured, and body mass index was calculated. Time spent in moderate-to-vigorous physical activity was measured by accelerometry. Gross motor coordination was assessed with the KörperkoordinationsTest für Kinder battery and socio-economic status was obtained via the school social support system. School characteristics were obtained with an objective school audit. A multilevel analysis was used as implemented in Stata 15.

Results: Schools explained 18.2% of the total variance in moderate-to-vigorous physical activity, with the remainder being ascribed to children's distinct characteristics. Boys were more active (β=29.59±11.52, p<0.05), and having higher gross motor coordination levels (β=0.11±0.04, p<0.05) was positively associated with daily moderate-to-vigorous physical activity, whereas being older (β=-5.00±1.57, p<0.05) and having higher socio-economic status (β=-7.89±3.12, p<0.05) were negatively related with moderate-to-vigorous physical activity. From the school-level correlates, only playground dimension was significantly associated with moderate-to-vigorous physical activity levels. Children from schools with medium (40m to 69m) and large playground dimensions (≥70m) were less active than children with smaller playground dimensions (10m to 39m).

Conclusions: Variation in school children's moderate-to-vigorous physical activity is mostly explained by their individual characteristics; school characteristics also play a role but to a smaller degree. Future intervention programs to change this behavior should be more personalized, emphasizing mostly individual-level characteristics.