The consequences of using different epoch lengths on the classification of accelerometer based sedentary behaviour and physical activity

PLoS One. 2021 Jul 15;16(7):e0254721. doi: 10.1371/journal.pone.0254721. eCollection 2021.

Abstract

We examined the influence of using different epoch lengths on the classification accuracy of laboratory-controlled sedentary behaviour (SB), and free-living total time and time spent in bouts of SB and moderate-to-vigorous physical activity (MVPA), in children and adolescents. We used two studies including accelerometer-derived data of: 1) controlled activities, i.e. seven sedentary, one standing and one dancing (n = 90); 2) free-living activities (n = 902). For the controlled-activity data, we calculated percentages of time classified as SB and MVPA. For the free-living data, we calculated medians (25th-75th percentiles) of total time and time spent in bouts of SB and MVPA. Applying 8counts/5seconds, 25counts/15seconds and 100counts/60seconds for SB on controlled-activity data revealed respectively (1) 92-96%, 89-99% and 98-100% of sedentary time accurately classified as SB (activity- and age-dependent); (2) 91-98%, 88-99% and 97-100% of standing time classified as SB (age-dependent); (3) 25-37%, 20-25% and 25-38% of dancing time classified as SB (age-dependent). Using longer epochs, children's total time in SB and MVPA decreased while time accumulated in bouts of SB and MVPA accumulated in bouts increased. We conclude that a 60-second epoch seems preferable when the aim is to classify sedentary behaviour, while a shorter epoch length is needed to capture children's short bursts of MPVA. Furthermore, we should be aware that a longer epoch results in averaging of intensities to the middle category.

Grant support

The contributions of Altenburg, Wang, van Ekris and Chinapaw were funded by the Netherlands Organization for Health Research and Development (Grant number 91211057). The contribution of Wang was further funded by the National Natural Science Foundation of China (NSF 61263039 and 11101321) and the Qinghai Science & Technology Department Project (QHSTDP 2017-ZJ-768 and QHSTDP 2018-ZJ-776). We would like to thank prof Niels Wedderkopp University of Southern Denmark for providing us data from the CHAMPS study. The CHAMPS-study was funded by: The TRYG Foundation, University College Lillebaelt, University of Southern Denmark, The Nordea Foundation, The IMK foundation, The Region of Southern Denmark, The Egmont Foundation, The A.J. Andersen Foundation, The Danish Rheumatism Association, Østifternes Foundation, Brd. Hartmann’s Foundation, TEAM Denmark, The Danish Chiropractor Foundation, The Nordic Institute of Chiropractic and Clinical Biomechanics. The funding organisations had no role in this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.