Mattocks Calum, Leary Sam, Ness Andy, Deere Kevin, Saunders Joanne, Kirkby Joanne, Blair Steven N, Tilling Kate, Riddoch Chris
Department of Social Medicine, University of Bristol, United Kingdom.
Med Sci Sports Exerc. 2007 Apr;39(4):622-9. doi: 10.1249/mss.0b013e318030631b.
This study examined the seasonal and intraindividual variation in objectively measured physical activity in 11- to 12-yr-olds.
Children were asked to wear a uniaxial accelerometer for 7 d four times throughout the course of about a year. A random-intercepts model was used to separate the inter- and intraindividual components of physical activity. Gender, age, body mass index (BMI), height, and month of measurement were fitted to the model as potential confounders.
A total of 315 children had valid data for at least two measurement occasions, and 244 had data for all four measurement occasions. The unadjusted intraclass correlation coefficient (ICC) for total activity (counts per minute) was 0.54; 0.49 after adjusting for gender, age, and BMI; and 0.53 after adjusting for gender, age, BMI, and month. Further adjustment for pubertal status at baseline had no effect on the ICC. Restricting the analysis to only those with data for all four measurement occasions (N=244), or to measurements taken on school days only, had no effect on the ICC. The fully adjusted ICC was 0.51 for weekdays only and 0.39 for weekend days only. For minutes of moderate to vigorous physical activity, minutes of vigorous activity, minutes of sedentary behavior, and number of 30-min blocks of sedentary behavior, the fully adjusted ICC were 0.45, 0.37, 0.59, and 0.39, respectively. The analysis was repeated for boys and girls separately, but the differences in ICC were small.
There was substantial intraindividual variation in the objectively measured physical activity of these children. Studies using single a measurement occasion where physical activity is the exposure should take this into account to adjust for regression dilution.
本研究调查了11至12岁儿童客观测量的身体活动的季节性和个体内差异。
在大约一年的时间里，让儿童四次佩戴单轴加速度计，每次佩戴7天。使用随机截距模型来分离身体活动的个体间和个体内成分。将性别、年龄、体重指数（BMI）、身高和测量月份作为潜在混杂因素纳入模型。
共有315名儿童至少有两次测量的有效数据，244名儿童有全部四次测量的数据。总活动量（每分钟计数）的未调整组内相关系数（ICC）为0.54；在调整性别、年龄和BMI后为0.49；在调整性别、年龄、BMI和月份后为0.53。进一步调整基线时的青春期状态对ICC没有影响。将分析仅限于那些有全部四次测量数据的儿童（N = 244），或仅限于上学日进行的测量，对ICC没有影响。仅工作日的完全调整后的ICC为0.51，仅周末日的为0.39。对于中度至剧烈身体活动分钟数、剧烈活动分钟数、久坐行为分钟数以及30分钟久坐行为时段数，完全调整后的ICC分别为0.45、0.37、0.59和0.39。分别对男孩和女孩重复进行分析，但ICC的差异很小。
这些儿童客观测量的身体活动存在显著个体内差异。以身体活动为暴露因素的单测量时点研究应考虑到这一点以调整回归稀释。
