The Effect of Reintegrating Accelerometer Counts In Preschool Children: Comparison Using Different Epoch Lengths
The purpose of this study was to determine whether ActiGraph accelerometer activity counts and estimates of moderate-to-vigorous physical activity (MVPA) collected at a criterion epoch (e.g., 60s epoch) are comparable in relation to those collected at smaller epochs (e.g., 1s epoch) then reintegrated into a larger epoch (e.g., 60 consecutive 1s epochs summed to create 1 60s epoch). Thirty-one preschoolers (3-5yrs) concurrently wore four accelerometers initialized at four epoch lengths (i.e., 1s, 15s, 30s, and 60s) during a full preschool day. Activity counts collected at 1s, 15s, 30s epoch each were reintegrated and compared to counts collected at a larger epoch length (i.e., consecutive sum of activity counts from 15 1s epochs = activity counts from 1 15s epoch). Four sets of cut-points (i.e., Pate, Puyau, Sirard, and Van Cauwenberghe) were used to estimate minutes spent in MVPA. The following comparisons were made for counts and MVPA: 15s, 30s and 60s epoch vs. 1s epoch reintegrated, 30s and 60s epoch vs. 15s epoch reintegrated, and a 60s epoch vs. 30s epoch reintegrated. Paired t-test and Cohen's d were used to compare group mean differences between criteria epochs and reintegrated epochs. Absolute percent errors (APE) and Bland Altman (BA) plots with limits of agreement (LoA) were used to identify variations in individual comparisons. No statistically significant group mean differences were found for activity counts and MVPA estimates between criteria and reintegrated epochs. Small Cohen's ds for activity counts (range -0.02 to 0.00) and for MVPA estimates (range -0.02 to 0.02) were observed. Small APEs (range 6.2% to 9.2%) for activity counts were observed, whereas larger APEs for MVPA estimates (range 13.0% to 50.3%) were observed. BA plot with LoA showed no systematic pattern of bias for activity counts and MVPA estimates. Small differences in activity counts are likely to result in larger individual variations in estimates of MVPA, although group mean differences are minimal. Therefore, researchers measuring physical activity at smaller epochs and reintegrating should be conscious of possible differences in MVPA estimates obtained from a criterion epoch.
Exercise Science, Kinesiology, Life Sciences
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