Carroll J P, Freedman W
Pennsylvania College of Optometry, Philadelphia.
J Biomech. 1993 Apr-May;26(4-5):409-16. doi: 10.1016/0021-9290(93)90004-x.
Postural sway during quite stance is usually assumed to be a stationary stochastic process. We tested this assumption by investigating the time invariance of the average value and variance of the postural sway of three subjects. The sway was measured with a force plate under three conditions: subject standing on two feet with eyes open; subject standing on two feet with eyes closed; and subject standing on one foot with eyes open. Data were collected in 1 min runs. More than 50 min of data were collected for each subject under each test condition. The data were averaged across all runs for each subject and condition. Trends were found to be present in the data. In addition, there were initial transient increases in the second-order moments about the trends. The transient changes in first- and second-order moments usually disappeared during the first 20 s. In light of these findings, we can reject the hypothesis that postural sway is a stationary process. The results imply that the usual methods to parameterize postural sway have to be either changed or reinterpreted.
安静站立时的姿势晃动通常被认为是一个平稳随机过程。我们通过研究三名受试者姿势晃动平均值和方差的时间不变性来检验这一假设。在三种条件下用测力板测量晃动：受试者双脚睁眼站立；受试者双脚闭眼站立；受试者单脚睁眼站立。数据以1分钟的时间段收集。在每种测试条件下，为每个受试者收集了超过50分钟的数据。对每个受试者在每种条件下的所有时间段的数据进行平均。发现数据中存在趋势。此外，围绕这些趋势的二阶矩最初有短暂增加。一阶和二阶矩的瞬态变化通常在最初20秒内消失。鉴于这些发现，我们可以拒绝姿势晃动是平稳过程的假设。结果表明，通常用于参数化姿势晃动的方法必须改变或重新解释。
