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Abstract
Background
The Canadian Health Measures Survey uses accelerometry to collect physical activity and sedentary behaviour data. Between cycles 2 and 3, a transition was made from 60-second to 15-second epochs in accelerometry data for children aged 3 to 5. This study examines the impact of epoch length on physical activity and sedentary behaviour outcomes.
Data and methods
Twenty-nine children aged 3 to 5 wore two accelerometers at the same time, one initialized to collect data in 60-second epochs, and the other, in 15-second epochs. Comparisons between epoch settings were made for several physical activity variables.
Results
Compared with the 60-second epoch setting, the 15-second setting captured more moderate-to-vigorous physical activity (MVPA) and sedentary time, but fewer steps and less light and total physical activity. The correlation between epoch settings was high for all variables except steps.
Interpretation
The epoch length used in accelerometer data collection affects physical activity and sedentary behaviour data for preschool-aged children.
Keywords
Ambulation, pediatric, stepping, walking
The Canadian Health Measures Survey (CHMS) uses accelerometry to directly measure physical activity and sedentary behaviour. Accelerometers record movement data at defined intervals called "epochs." The epoch length used in research ranges from less than one second to one minute.
The use of accelerometry to measure physical activity among preschool-aged children presents unique challenges because their movement is more sporadic and intermittent than that of older children and adults.1 Research has shown that collecting accelerometer data in shorter rather than longer epochs captures more moderate-to-vigorous physical activity (MVPA) in young children. As a result, the use of longer epoch lengths for this population has been questioned. A consensus is emerging that shorter epochs should be used for preschool-aged children to ensure that short bursts of movement are recorded.2-4
Determination of MVPA levels among preschool-aged children is important because MVPA is a component of new guidelines that recommend 180 minutes a day of physical activity of any intensity for 0- to 4-year-olds, with a progression toward 60 minutes of MVPA by age 5.5 Obeid et al. found that, when compared with 3-second epochs, the use of 15-, 30- and 60-second epochs resulted in averages of 2.9, 9.0 and 16.7 "missed" minutes of MVPA per day, respectively.3 Another study reported 17 minutes more MVPA...