Molecular Epidemiology Group, Max Delbrueck Center for Molecular Medicine in the Helmholtz Association (MDC), Robert-Roessle-Strasse 10, 13125, Berlin, Germany.
Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany.
BMC Public Health. 2018 Apr 20;18(1):530. doi: 10.1186/s12889-018-5415-8.
24 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.
We 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.
Between- 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).
Individual 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.
24 小时加速计现在用于许多观察性研究中客观评估身体活动（PA），例如德国国家队列研究；然而，PA 变异性、估计习惯性 PA 所需的观察时间和可靠性尚不清楚。
我们使用三轴加速度计（ActiGraph GT3X+）在两周内对 50 名参与者的 24 小时 PA 进行了评估。使用线性混合效应和随机效应模型来量化评估日或周内 PA 整体和不同 PA 强度（无活动和低强度、中强度、高强度和极高强度 PA 时间）的变异性。我们计算了估计 PA 所需的天数，并使用组内相关系数计算了 PA 可靠性。
两周内，个体间和个体内方差分别占 PA 整体和 PA 强度总方差的 34.4%-45.5%和 54.5%-65.6%。PA 整体和低强度、中强度和高强度 PA 的时间在评估的前 3 天略有下降。PA 整体（p=0.03）、无活动时间（p=0.003）、低强度 PA 时间（p=0.001）、中强度 PA 时间（p=0.02）和高强度 PA 时间（p=0.04）在一周中的不同日子略有不同，星期三和星期五最高，星期日和星期一最低，星期六和星期日之间存在明显差异。在嵌套随机模型中，周几只占 PA 参数总方差的<19%。平均而言，估计习惯性 PA 所需的天数约为 1 周，PA 整体为 7 天，PA 强度从 6 天到 9 天不等。周间可靠性良好（组内相关系数，范围为 0.68-0.82）。
使用 24 小时加速计评估的个体 PA 在天与天之间差异很大，但评估日或周几只解释了这种差异的一小部分。我们的数据表明，需要进行 1 周的评估才能可靠地估计习惯性 PA。
