Variability and reliability study of overall physical activity and activity intensity levels using 24\xa0h-accelerometry-assessed data

Lina Jaeschke,Stephanie Jeran,Tobias Pischon,Astrid Steinbrecher,Stefan Konigorski

doi:10.1186/s12889-018-5415-8

Abstract

Background24 h-accelerometry is now used to objectively assess physical activity (PA) in many observational studies like the German National Cohort; however, PA variability, observational time needed to estimate habitual PA, and reliability are unclear.MethodsWe assessed 24 h-PA of 50 participants using triaxial accelerometers (ActiGraph GT3X+) over 2 weeks. Variability of overall PA and different PA intensities (time in inactivity and in low intensity, moderate, vigorous, and very vigorous PA) between days of assessment or days of the week was quantified using linear mixed-effects and random effects models. We calculated the required number of days to estimate PA, and calculated PA reliability using intraclass correlation coefficients.ResultsBetween- and within-person variance accounted for 34.4–45.5% and 54.5–65.6%, respectively, of total variance in overall PA and PA intensities over the 2 weeks. Overall PA and times in low intensity, moderate, and vigorous PA decreased slightly over the first 3 days of assessment. Overall PA (p = 0.03), time in inactivity (p = 0.003), in low intensity PA (p = 0.001), in moderate PA (p = 0.02), and in vigorous PA (p = 0.04) slightly differed between days of the week, being highest on Wednesday and Friday and lowest on Sunday and Monday, with apparent differences between Saturday and Sunday. In nested random models, the day of the week accounted for < 19% of total variance in the PA parameters. On average, the required number of days to estimate habitual PA was around 1 week, being 7 for overall PA and ranging from 6 to 9 for the PA intensities. Week-to-week reliability was good (intraclass correlation coefficients, range, 0.68–0.82).ConclusionsIndividual PA, as assessed using 24 h-accelerometry, is highly variable between days, but the day of assessment or the day of the week explain only small parts of this variance. Our data indicate that 1 week of assessment is necessary for reliable estimation of habitual PA.

Highlights

24 h-accelerometry is used to objectively assess physical activity (PA) in many observational studies like the German National Cohort; PA variability, observational time needed to estimate habitual PA, and reliability are unclear
In most studies focusing on reliability published so far, accelerometers were worn by participants during waking hours only and many have used the older generation of uniaxial accelerometers [9, 10, 12, 13]
The aim of this study was to quantify the variability of overall PA and of time spent in different PA intensities assessed through 24 h-accelerometry in a general adult population

Summary

Introduction

24 h-accelerometry is used to objectively assess physical activity (PA) in many observational studies like the German National Cohort; PA variability, observational time needed to estimate habitual PA, and reliability are unclear. Little information is currently available about the variation of overall PA and time spent in different PA intensities on a 24 h day-to-day basis, and about the number of days necessary to estimate habitual PA especially with regard to intensity levels. Such information is important, since in epidemiologic studies one is usually interested in the ‘average’ PA amount, in order to estimate to what extent persons with higher or lower PA levels differ in chronic disease risk. High within-person variability or low between-person variability will require more repeated assessments to estimate habitual PA

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