Abstract
BackgroundAccelerometry non-wear time rules might affect sedentary time, and the associations with health outcomes such as adiposity. However, the exact effect of different non-wear time rules on sedentary time and reported changes in sedentary time is unknown. This study evaluated the effect of different accelerometry non-wear time rules on sedentary time and changes in sedentary time from age 9–12 years.MethodsAccelerometry data were collected as part of the Gateshead Millennium Birth Cohort study. Participants were 9.3 (±0.4) years at baseline (n = 517) and 12.5 (±0.3) years at follow-up (n = 440). Sedentary time was defined using an accelerometry cut-point of 25 counts per 15 s. Non-wear time was defined using manual data reduction (the reference method) and 10 min, 20 min and 60 min consecutive zeros. Differences between methods were analyzed using repeated measures ANOVA with Bonferroni post-hoc analyses.ResultsMean daily sedentary time at age 9 ranged from 364 min per day to 426 min using the 10 min and 60 min rule, respectively (p < 0.05). At 12 years, mean daily sedentary times ranged from 424 min to 518 min (p < 0.05). Mean changes in daily sedentary time over the three years ranged from 60 min to 93 min using the 10 min and 60 min rule, respectively (p < 0.05). When adjusting for wear time, differences in average sedentary time between methods decreased from 62 min to 27 min (age 9), 95 min to 32 min (age 12) and 33 min to 10 min (changes between 9 to 12 years).ConclusionsUsing different non-wear time rules results in significant differences in daily sedentary time and changes in sedentary time. Correcting for wear time appears to be a reasonable approach to limiting these differences and may improve comparability between future studies. Using the 20 min rule, while correcting for wear time, provided the most accurate estimates of sedentary time and changes in sedentary time, compared to the manual reference in 9–12 year-olds.
Highlights
Accelerometry non-wear time rules might affect sedentary time, and the associations with health outcomes such as adiposity
Of the 517 children measured at baseline at age 9, 369 had valid measures at age 12 and were included in the analysis when looking at change in sedentary behavior
For the 440 participants included at age 12 the difference between rules increased, with average sedentary times ranging from 424 min per day to 518 min per day for the 10 min and 60 min zero string rules, respectively
Summary
Accelerometry non-wear time rules might affect sedentary time, and the associations with health outcomes such as adiposity. The exact effect of different non-wear time rules on sedentary time and reported changes in sedentary time is unknown. This study evaluated the effect of different accelerometry non-wear time rules on sedentary time and changes in sedentary time from age 9–12 years. To date the effect of different cut-points, minimum wear time and minimum number of valid days on physical activity and sedentary behavior outcomes have been examined [6, 7]. Much less is known about the effect of non-wear time criteria on sedentary time and reported changes of sedentary time. As sitting often results in zero counts and is most likely to occur in bouts, rather than sporadic episodes, the chosen length of consecutive zeros may influence the amount of sedentary time reported. Using inconsistent rules makes comparison of sedentary time, and changes in sedentary time, between studies very difficult [15]
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