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Measuring physical activity using accelerometry in 13–15-year-old adolescents: the importance of including non-wear activities

Abstract Objective The present study aimed to examine the impact of non-wear activities registered in diaries when using accelerometers to assess physical activity (PA) in young adolescents. Design Data arise from a large-scale cross-sectional study on PA. PA was objectively assessed using Actigraph™ accelerometers (Actigraph MTI, Manufacturing Technology Inc., Pensacola, FL, USA) during seven consecutive days. Non-wear time activity diaries were provided to register the activities for which the accelerometer was removed. After correction to deal with over-reporting, the registered minutes of PA were used to replace periods of non-wear time measured by the accelerometer. Setting Between October 2008 and May 2009 adolescents were recruited by home visits in Ghent (Belgium). Subjects Young adolescents (n 513; 48·6 % boys) aged 13 to 15 years. Results Of the total sample, 49·9 % registered at least one activity of moderate to vigorous intensity in the non-wear time activity diary. More adolescents registered an activity performed on a weekday than on a weekend day and the registered mean number of minutes of moderate to vigorous PA were higher on weekend days. Repeated-measures (M)ANOVA tests revealed a significant difference between the mean minutes with and without non-wear activities for all PA intensities, regardless of adolescents’ socio-economic status or gender. More adolescents achieved the PA recommendations after inclusion of the non-wear activities irrespective of accelerometer thresholds used. Conclusions The collection of information regarding non-wear time by non-wear time activity diaries when using accelerometers in 13–15-year-old adolescents can lead to different PA outcomes at the individual level and therefore can improve the ability to accurately measure PA.