Longitudinal Changes in Children's Accelerometer-derived Activity Pattern Metrics

Purpose The objective of this study was to quantify age-related changes in accelerometer-derived day-level physical activity and sedentary behavior pattern metrics (i.e., number, length, and temporal dispersion of bouts and breaks) across 3 yr of middle childhood. Differences by child sex and weekend versus weekday were examined. Method Children (N = 169, 54% female, 56% Hispanic; 8-12 yr old at enrollment) participated in a longitudinal study with six assessments across 3 yr. Day-level moderate-to-vigorous physical activity (MVPA; i.e., total minutes, number of short (<10 min) bouts, proportion of long (>= 20 min) bouts, temporal dispersion) and sedentary behavior (i.e., total minutes, number of breaks, proportion of long (>= 60 min) bouts, temporal dispersion) pattern metrics were measured using a waist-worn accelerometer (Actigraph GT3X). Results Random intercept multilevel linear regression models showed that age-related decreases in the number of short MVPA bouts per were steeper for girls than for boys (b = -1.28; 95% confidence interval (CI), -1.93 to -0.64; P < 0.01) and on weekend days than on weekdays (b = -1.82; 95% CI, -2.36 to -1.29; P < 0.01). The evenness of the temporal dispersion of MVPA across the day increased more on weekend days than on weekdays as children got older (b = -0.02; 95% CI, -0.02 to -0.01; P < 0.01). Girls had steeper age-related decreases in the number of sedentary breaks per day (b = -2.89; 95% CI, -3.97 to -1.73; P < 0.01) and the evenness of the temporal dispersion of sedentary behavior across the day (b <= 0.01; 95% CI, P < 0.01) than did boys. Changes in sedentary behavior metrics did not differ between weekend days and weekdays. Conclusion Strategies to protect against declines in short physical activity bouts and promote sedentary breaks, especially among girls and on weekend days, could reduce cardiometabolic risks.