Abstract
OBJECTIVES: Later achievement of standing and walking in infancy predicts childhood physical inactivity. This study aimed to examine associations between ages of achieving six gross motor milestones and childhood physical activity, and whether these associations were mediated by adiposity. DESIGN: A retrospective analysis of a subset from a cohort study. METHODS: Data were available for 211 first-grade primary school children (aged 6-7 years) in the Kanto region, Japan. Information on ages of achieving holding head up, sitting, crawling, standing supported, walking supported, and independent walking were obtained from parental records in the Maternal and Child Health Handbooks. Adiposity was assessed using dual-energy X-ray absorptiometry, and expressed as body fat percentage. Current gross motor skills were assessed by the Test of Gross Motor Development 2nd edition. Physical activity was measured using a triaxial accelerometer and defined as time involved in moderate-to-vigorous-intensity physical activity (MVPA). RESULTS: Multiple regression analyses revealed that the age of achieving standing supported was negatively associated with MVPA (p = .021), while ages of achieving crawling (p = .010), standing supported (p = .002), and walking supported (p = .033) were positively associated with adiposity, after adjusting for potential confounders including current gross motor skills. When adiposity was introduced as a covariate, the age of achieving standing supported was still associated with MVPA (p = .048), and the indirect effect of achievement of standing supported on MVPA was not significant. CONCLUSIONS: Infants who achieve standing supported at a later age are less likely to be active during early school age, and adiposity may not mediate this association.