Physical Activity, Sedentary Time, and Fatness in a Biethnic Sample of Young Children

Purpose: This study aimed to investigate associations of objectively measured physical activity (PA) and sedentary time with adiposity in a predominantly biethnic (South Asian and White British) sample of young children. Methods: The sample included 333 children age 11 months to 5 yr who provided 526 cross-sectional observations for PA and body composition. Total PA volume (vector magnitude counts per minute), daily time at multiple intensity levels (the cumulative time in activity >500, >1000, >1500, ... I, >6000 counts per minute), and time spent sedentary (<820 counts per minute), in light PA (820-3907 counts per minute) and in moderate-to-vigorous PA (>= 3908 counts per minute) were estimated with triaxial accelerometry. Indicators of adiposity included body mass index, waist circumference, and the sum of subscapular and triceps skinfold thicknesses. Statistical analyses were performed using multilevel regression and isotemporal substitution models adjusted for confounders. Effect modification by ethnicity was examined. Results: There was no evidence for effect modification by ethnicity (P interaction >= 0.13). In the whole sample, the accumulated time spent above 3500 counts per minute (i.e., high light-intensity PA) was inversely associated with the sum of skinfolds (beta = -0.60 mm, 95% confidence interval [CI] = -1.19 to -0.021, per 20 minId(-1)), and the magnitude of association increased dose dependently with PA intensity (peaking for time spent >6000 counts per minute = -1.57 mm, 95% CI = -3.01 to -0.12, per 20 minId(-1)). The substitution of 20 minId(-1) of sedentary time with moderate-to-vigorous PA was associated with a lower sum of skinfolds (-0.77 mm, 95% CI = -1.46 to -0.084). Conclusions: High light-intensity PA appears to be beneficial for body composition in young South Asian and White British children, but higher-intensity PA is more advantageous.