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Open Access Research article

Epoch length and the physical activity bout analysis: An accelerometry research issue

Makoto Ayabe1*, Hideaki Kumahara12, Kazuhiro Morimura1 and Hiroaki Tanaka1

Author Affiliations

1 Faculty of Health and Sports Science, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan

2 Faculty of Nutritional Sciences, Nakamura Gakuen University, Fukuoka, Japan

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BMC Research Notes 2013, 6:20  doi:10.1186/1756-0500-6-20

Published: 18 January 2013

Abstract

Background

The purpose of the present investigation was to compare the bouts of daily physical activity (PA) determined by three different accelerometer epoch lengths under free-living conditions.

Methods

One hundred thirty-four adults (50 ± 7 years) wore an accelerometer (Lifecorder) for 7 consecutive days under free-living conditions in order to determine the time spent in physical activity of light intensity (LPA), moderate intensity (MPA), vigorous intensity (VPA), moderate to vigorous intensity (MVPA), and the total physical activity (TPA; sum of LPA, MPA and VPA). Additionally, all PA was divided according to the bout durations (sporadic, >3 min, >5 min, and > 10 min). These indices of PA were analyzed using three different epoch lengths (4 sec, 20 sec and 60 sec) derived from the accelerometer.

Results

The LPA significantly increased in association with increases in the epoch length (48.7 ± 15.9 to 178.7 ± 62.6 min/day, p < 0.05). The amount of sporadic VPA determined by the shortest epoch length (2.9 ± 5.2 min/day) was significantly longer than the two remaining epoch lengths (1.1 ± 2.4 to 0.9 ± 2.5 min/day, p < 0.05). The times of the MVPA bouts lasting longer than 3 minutes determined using the 4-second epoch length (2.6 ± 5.4 to 7.7 ± 10.0 min/day) were significantly shorter than those determined using the other two settings (6.5 ± 10.5 to 13.8 ± 13.8 min/day, p < 0.05). The frequencies of the MVPA bouts lasting longer than 10 minutes determined using the 4-second epoch length (0.2 ± 0.3 bouts/day) were significantly lower than those determined using the other two settings (0.3 ± 0.4 bouts/day, p < 0.05).

Conclusion

The epoch length setting of the accelerometer affects the estimation of the PA bouts under free-living conditions in middle-aged to older adults.

Keywords:
Accelerometer; Pedometer; Pedometry; Methodology; Accuracy; Validity