The characteristics of postural sway were assessed in quiet standing under three different postural task conditions in 14 patients with nonspecific chronic low back pain and 12 healthy subjects using linear and nonlinear center of pressure parameters. The linear parameters consisted of area, the mean total velocity, sway amplitude, the SD of velocity, and the phase plane portrait. The nonlinear parameters included the Lyapunov exponent, sample entropy, and the correlation dimension. The results showed that the amount of postural sway was higher in the patients with low back pain compared with the healthy subjects. Assessing the nonlinear parameters of the center of pressure showed a lower sample entropy and a higher correlation dimension in the patients with low back pain compared with the healthy subjects. The results of this study demonstrate the greater regularity and higher dimensionality of the center of pressure fluctuations in patients with nonspecific chronic low back pain, which suggests that these patients adopt different postural control strategies to maintain an upright stance.

中文翻译：

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慢性下腰痛患者安静站立期间压力波动中心的数量和时间结构。

使用线性和非线性压力中心参数，在14种非特异性慢性下腰痛患者和12名健康受试者的三种不同姿势任务条件下，在安静站立时评估姿势摇摆的特征。线性参数由面积，平均总速度，摇摆幅度，速度的SD和相平面肖像组成。非线性参数包括李雅普诺夫指数，样本熵和相关维。结果表明，与健康受试者相比，腰背痛患者的姿势摇摆量更高。与健康受试者相比，腰痛较低的患者评估压力中心的非线性参数显示较低的样本熵和较高的相关维度。