Physical activity and inactivity trajectories associated with body composition in pre-schoolers

Background/objectives Early childhood is characterised by rapid development and is a critical period for the establishment of activity behaviours. We aim to examine how physical activity (PA) and sedentary behaviour (SB) track during the first 5 years of life, and to investigate associations between trajectories and body composition at 5 years of age. Subjects/methods A total of 438 participants (50% male) wore an Actical accelerometer for 5 days at at least two of 1, 2, 3.5 and 5 years of age. Spearman correlation coefficients examined PA tracking from age 1 to 5 and trajectories of PA and SB were estimated using discrete mixture modelling. Regression models tested associations between both PA and SB trajectories and body composition measures. Results Tracking coefficients for PA ranged from r = 0.31-0.51 across the ages, with similar tracking observed for sedentary behaviour (r = 0.21-0.39). Four distinct trajectory patterns were identified separately for PA and SB: consistently low, consistently high, increasing and decreasing. BMI and waist circumference were not significantly associated with PA trajectories, but those in the consistently high activity group had significantly lower % body fat (95% CI) at age 5 (14.3%; 13.5, 15.2) than those in the consistently low (16.8%; 15.6, 18.2) or increasing (15.7%; 14.7, 16.7) groups (P = 0.017). Sedentary behaviour trajectories were not associated with any of the anthropometric measures at age 5 (P > 0.05). Conclusions Physical activity and sedentary behaviour tracking is broadly similar from infancy to early childhood. Children with consistently higher levels of physical activity have reduced body fat at 5 years of age, although differences are relatively small.