Bi-directional associations between physical activity and growth indicators of pre-school aged children.

Physical activity for young children provides a wealth of benefits for health and development. However, little is known about the inter-relationship of physical activity and growth indicators. The aim of this study was to test the bi-directional associations of physical activity and growth indicators in children under five years of age. This prospective study included 1,575 children with data on physical activity and growth indicators at ages 12, 24 and 48 months. Accelerometers were used to measure physical activity. Z-scores for length/height-for-age, weight-for-length/height, weight-for-age and body mass index (BMI)-for-age were calculated. Bi-directional associations between physical activity and growth indicators were evaluated using cross-lagged panels based on Generalized Estimating Equations and cross-lagged structural equation models. Physical activity was consistently associated with lower weight-related growth indicators: BMI-for-age: β=-0.12; Weight-for-age: β=-0.11; Weight-for-length/height: β=-0.12. Higher BMI-for-age indicated lower physical activity (β=-0.06). When the exposure was lagged, the association of physical activity on weight-related growth indicators remained, but weight-related growth indicators showed a negative association on physical activity. A bi-directional association between physical activity and weight-related growth indicators was observed. The magnitude of associations were stronger when physical activity was modelled as exposure. These results reinforce the importance of physical activity since early years.