Accelerometer epoch length influence associations for physical activity intensities with body mass index and locomotor skills in young children

The epoch length is decisive for the capture of physical activity intensities from accelerometry and possibly for associations between physical activity intensities and outcomes in children. The aim of the present study was to determine the multivariate physical activity intensity signatures related to body mass index and locomotor skills in preschool children using different epoch lengths. A sample of 1054 Norwegian children (mean age 4.8 years, 52% boys) from the Sogn og Fjordane Preschool Physical Activity Study provided data on physical activity (ActiGraph GT3X+), body mass index and locomotor skills in 2015-2016. Multivariate pattern analysis was used to determine associations between the physical activity intensity spectrum (0-99 to ≥15000 counts per minute) and the outcomes using files aggregated using 8 different epoch lengths from 1 to 60 seconds. We observed that associations across the intensity spectrum, from sedentary time to vigorous intensities, differed for data derived using different epoch lengths. For both outcomes, associations for moderate intensities became stronger and vigorous intensities became weaker for longer as compared to shorter epoch lengths. Aggregation of accelerometer data using different epoch lengths influences the capture of physical activity intensities and associations between physical activity intensities and related outcomes.