From sedentary time to sedentary patterns: Optimal accelerometer data reduction decisions in children

Purpose: This study aims to establish evidence-based accelerometer data reduction criteria to accurately assess sedentary patterns in children. We not only examined total sedentary time, but also duration and number of breaks and uninterrupted sedentary bouts.

Methods: Participants (n=1057 European children; aged 10-12 yrs) wore an ActiGraph accelerometer for at least 6 consecutive days. We explored 1) the most realistic criterion for non-wear time, 2) differences between 8 and 10 hours valid wear time per day; 3) differences between weekday and weekend day regarding total sedentary time, duration and number of prolonged sedentary bouts and the number of breaks; 4) the number of days of accelerometer wear to represent sedentary patterns.

Results: More than 60 consecutive minutes of zero counts was the optimal criterion for non-wear time, based on frequency of non-wear time periods. Increasing the definition for a valid day from 8 to 10 hours wear time hardly influenced sedentary outcomes while the sample size of children with at least five valid days increased from 69 to 81%. On weekdays children had 1hr more wear time, 50min more total sedentary time, and 26 min more sedentary time accumulated in bouts. At least 6 days of accelerometer data were needed to accurately represent sedentary patterns.

Conclusions: We recommend 1) a minimum of 60 minutes of consecutive zeros as the most realistic criterion for non-wear time; and 2) including at least six days with minimum eight valid hours to characterize children’s usual sedentary patterns, preferably including at least one weekend day.