The effect of reintegrating Actigraph accelerometer counts in preschool children: Comparison using different epoch lengths

ObjectivesThe purpose of this study was to determine whether ActiGraph accelerometer activity counts and estimates of moderate-to-vigorous physical activity collected at a single larger epoch are comparable to those collected at smaller epochs reintegrated into a larger epoch.DesignA cross-sectional study design.MethodsThirty-one preschoolers (3–5 years) concurrently wore four accelerometers that were each initialized at four different epoch lengths (1 s, 15 s, 30 s, and 60 s) during a full preschool day. Counts collected at 1 s, 15 s, and 30 s epoch were each reintegrated and compared to those collected at a larger epoch (e.g., counts from one 15 s epoch vs. consecutive sum of counts from fifteen 1 s epochs). Six sets of cut-points (Pate, Freedson, Sirard, Van Cauwenberghe, Evenson and Puyau) were applied to estimate moderate-to-vigorous physical activity minutes. Paired t-test and Cohen's d were used to compare group mean differences. Absolute percent errors Bland–Altman plots with limits of agreement were used to compare individual differences.ResultsMinimal group mean differences were found for counts and moderate-to-vigorous physical activity estimates between larger and reintegrated epochs. Relatively smaller absolute percent errors (6.2–9.2%) and limits of agreements (−15.52%, 18.00% to −28.27%, 28.02%) were observed for counts than absolute percent errors (10.1–50.3%) and limits of agreements (−27.3%, 33.3% to −156.9%, 137.9%) for moderate-to-vigorous physical activity estimates.ConclusionsSmaller individual differences in activity counts tended to yield larger individual variations in moderate-to-vigorous physical activity estimates, despite minimal group mean differences. Therefore, researchers reintegrating smaller epochs into a larger epoch should be conscious of possible differences in moderate-to-vigorous physical activity estimates obtained from a single larger epoch.