Importance of epoch length and registration time on accelerometer measurements in younger children.

AIM: The aim of this study was to investigate the effect of epoch length on accumulation of minutes of physical activity per day over a spectrum of intensities, and the effect that selection of number of hours of acceptable registration required per day had on number of days that were considered acceptable. METHODS: Participants were 696 children (369 boys and 327 girls) aged 6.7±0.4 yrs, from a population-based cohort. Physical activity was assessed by the Actigraph accelerometer for four days. RESULTS: Main findings were that epoch length had a profound impact on accumulation of minutes of physical activity per day for higher intensities, whereas it had no effect on mean counts per minute. The chosen number of hours for an acceptable registration per day heavily influenced the number of days that were considered acceptable. CONCLUSION: The findings in the present investigation should be taken into consideration when planning objective measurements of daily physical activity in younger children, and highlight the need for setting international recommendations for physical activity measurements with accelerometers, if different studies are to be comparabl