Effects of epoch duration on estimated moderate and vigorous physical activity time among adults workers using the GT3X+ Accelerometer
DOI:
https://doi.org/10.12820/rbafs.31e0456Keywords:
Physical activity assessment, Accelerometry, MethodsAbstract
Introduction: Epoch length may influence physical activity estimates derived from accelerometers. Objective: To compare the effects of different epoch lengths on the average time spent in moderate-to-vigorous physical activity (MVPA) among adults using the GT3X+ accelerometer. Methods: This methodological study used data from the Longitudinal Study of Determinants of Physical Activity, a cohort of administrative staff and faculty members from a university in the state of Rio de Janeiro, Brazil.
Physical activity data were collected using an accelerometer (ActiGraph GT3X+) worn on the nondominant wrist for seven consecutive days. MVPA time was calculated using epoch lengths of 1s, 5s, 10s, 15s, 30s, and 60s. Analysis of variance was used to compare mean physical activity values across epoch lengths, followed by Bonferroni post hoc tests for pairwise comparisons. Bland–Altman plots were used to assess agreement. Accelerometer data processing and all statistical analyses were performed using R software. Results: A total of 255 participants were included (mean age: 44.0 ± 10.7 years; 55.3% men). Mean MVPA time was higher when calculated using shorter epochs compared with longer epochs (p < 0.001). MVPA estimated using a 1-second epoch was 94.8 minutes (95% CI: 90.6; 99.0), whereas the 60 second epoch yielded 67.4 minutes (95% CI: 62.8; 72.1), representing a significant mean difference of 27.7 minutes (p < 0.05). Conclusion: The observed differences indicate that substantially different epoch lengths may produce estimates that are difficult to compare and may lead to inaccurate conclusions. To improve comparability across studies using accelerometers, reporting the epoch length employed is essential.
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