Centre for Physical Activity and Nutrition Research, Deakin University, 221 Burwood Hwy, Burwood 3125 Melbourne, Australia.
Int J Behav Nutr Phys Act. 2012 Feb 19;9:15. doi: 10.1186/1479-5868-9-15.
Accelerometers have been used to determine the amount of time that children spend sedentary. However, as time spent sitting may be detrimental to health, research is needed to examine whether accelerometer sedentary cut-points reflect the amount of time children spend sitting. The aim of this study was to: a) examine agreement between ActiGraph (AG) cut-points for sedentary time and objectively-assessed periods of free-living sitting and sitting plus standing time using the activPAL (aP); and b) identify cut-points to determine time spent sitting and sitting plus standing.
Forty-eight children (54% boys) aged 8-12 years wore a waist-mounted AG and thigh-mounted aP for two consecutive school days (9-3:30 pm). AG data were analyzed using 17 cut-points between 50-850 counts·min-1 in 50 counts·min-1 increments to determine sedentary time during class-time, break time and school hours. Sitting and sitting plus standing time were obtained from the aP for these periods. Limits of agreement were computed to evaluate bias between AG50 to AG850 sedentary time and sitting and sitting plus standing time. Receiver Operator Characteristic (ROC) analyses identified AG cut-points that maximized sensitivity and specificity for sitting and sitting plus standing time.
The smallest mean bias between aP sitting time and AG sedentary time was AG150 for class time (3.8 minutes), AG50 for break time (-0.8 minutes), and AG100 for school hours (-5.2 minutes). For sitting plus standing time, the smallest bias was observed for AG850. ROC analyses revealed an optimal cut-point of 96 counts·min-1 (AUC = 0.75) for sitting time, which had acceptable sensitivity (71.7%) and specificity (67.8%). No optimal cut-point was obtained for sitting plus standing (AUC = 0.51).
Estimates of free-living sitting time in children during school hours can be obtained using an AG cut-point of 100 counts·min-1. Higher sedentary cut-points may capture both sitting and standing time.
加速度计已被用于确定儿童久坐时间的长短。然而，由于久坐时间可能对健康有害，因此需要研究以检查加速度计的久坐时间切点是否反映了儿童久坐的时间。本研究的目的是：a）检查 ActiGraph（AG）的久坐时间切点与客观评估的自由活动坐姿时间和坐姿加站立时间（使用 activPAL，aP）之间的一致性；b）确定确定坐姿和坐姿加站立时间的切点。
48 名 8-12 岁的儿童（54%为男孩）连续两天（9-3:30 pm）佩戴腰部佩戴的 AG 和大腿佩戴的 aP。AG 数据使用 17 个切点进行分析，切点在 50-850 计数·分钟-1 之间，间隔为 50 计数·分钟-1，以确定上课时间、课间休息时间和上课时间的久坐时间。在此期间，从 aP 中获得坐姿和坐姿加站立时间。计算了一致性界限，以评估 AG50 到 AG850 久坐时间与坐姿和坐姿加站立时间之间的偏差。接收器工作特征（ROC）分析确定了最大化坐姿和坐姿加站立时间的敏感性和特异性的 AG 切点。
AP 坐姿时间与 AG 久坐时间之间的平均偏差最小的是课堂时间的 AG150（3.8 分钟），课间休息时间的 AG50（-0.8 分钟），以及上课时间的 AG100（-5.2 分钟）。对于坐姿加站立时间，AG850 的偏差最小。ROC 分析显示，坐姿时间的最佳切点为 96 计数·分钟-1（AUC=0.75），具有可接受的敏感性（71.7%）和特异性（67.8%）。坐姿加站立时间没有最佳切点（AUC=0.51）。
在上课时间内，儿童的自由活动坐姿时间可以通过 AG 切点 100 计数·分钟-1 来估计。更高的久坐时间切点可能会同时捕获坐姿和站立时间。
