Physical Activity and Adiposity in a Racially Diverse Cohort of US Infants

Objective: Early life physical activity may help prevent obesity, but objective quantification in infants is challenging. Methods: A total of 506 infants were examined from 2013 to 2016. Infants wore accelerometers for 4 days at ages 3, 6, 9, and 12 months. Daily log-transformed physical activity counts were computed, averaged, and standardized across assessments. A linear mixed model was used to examine trends in standardized physical activity counts as well as associations between physical activity and BMI z score, sum of subscapular and triceps skinfold thickness for overall adiposity (SS+TR), and their ratio for central adiposity (SS:TR). Results: Among infants, 66% were black and 50% were female. For each additional visit, standardized physical activity counts increased by 0.23 (CI: 0.18 to 0.27; P < 0.0001). This translates to 126.3 unadjusted physical activity counts or a 4% increase for each visit beyond 3 months. In addition, a 1-SD increase in standardized physical activity counts (550 unadjusted physical activity counts) was associated with a 0.01-mm lower SS:TR (95% CI: −0.02 to −0.001; P = 0.03). However, standardized physical activity counts were not associated with BMI z score or SS+TR. Conclusions: Physical activity increased over infancy and was associated with central adiposity. Despite limitations, researchers should consider objective measurement in infants.