Moorhouse Kevin M, Granata Kevin P
Musculoskeletal Biomechanics Laboratories, Department of Engineering Science and Mechanics, School of Biomedical Engineering and Science, Virginia Polytechnic Institute and State University, Blacksburg, 24061, USA.
J Biomech. 2005 Oct;38(10):2000-7. doi: 10.1016/j.jbiomech.2004.09.014.
Spinal stability is related to the recruitment and control of active muscle stiffness. Stochastic system identification techniques were used to calculate the effective stiffness and dynamics of the trunk during active trunk extension exertions. Twenty-one healthy adult subjects (10 males, 11 females) wore a harness with a cable attached to a servomotor such that isotonic flexion preloads of 100, 135, and 170 N were applied at the T10 level of the trunk. A pseudorandom stochastic force sequence (bandwidth 0-10 Hz, amplitude +/-30 N) was superimposed on the preload causing small amplitude trunk movements. Nonparametric impulse response functions of trunk dynamics were computed and revealed that the system exhibited underdamped second-order behavior. Second-order trunk dynamics were determined by calculating the best least-squares fit to the IRF. The quality of the model was quantified by comparing estimated and observed displacement variance accounted for (VAF), and quality of the second-order fits was calculated as a percentage and referred to as fit accuracy. Mean VAF and fit accuracy were 87.8 +/- 4.0% and 96.0 +/- 4.3%, respectively, indicating that the model accurately represented active trunk kinematic response. The accuracy of the kinematic representation was not influenced by preload or gender. Mean effective stiffness was 2.78 +/- 0.96 N/mm and increased significantly with preload (p < 0.001), but did not vary with gender (p = 0.425). Mean effective damping was 314 +/- 72 Ns/m and effective trunk mass was 37.0 +/- 9.3 kg. We conclude that stochastic system identification techniques should be used to calculate effective trunk stiffness and dynamics.
脊柱稳定性与主动肌肉僵硬度的募集和控制有关。采用随机系统识别技术来计算主动伸展躯干时躯干的有效僵硬度和动力学特性。21名健康成年受试者（10名男性，11名女性）佩戴了一个安全带，安全带通过缆线连接到一个伺服电机，从而在躯干的T10水平施加100、135和170 N的等张屈曲预负荷。一个伪随机随机力序列（带宽0 - 10 Hz，幅度±30 N）叠加在预负荷上，引起小幅度的躯干运动。计算了躯干动力学的非参数脉冲响应函数，结果显示该系统呈现欠阻尼二阶行为。通过计算对脉冲响应函数的最佳最小二乘拟合来确定二阶躯干动力学。通过比较估计和观察到的位移方差贡献率（VAF）来量化模型的质量，二阶拟合的质量以百分比计算并称为拟合精度。平均VAF和拟合精度分别为87.8±4.0%和96.0±4.3%，表明该模型准确地代表了主动躯干运动学响应。运动学表示的准确性不受预负荷或性别的影响。平均有效僵硬度为2.78±0.96 N/mm，并且随着预负荷显著增加（p < 0.001），但不随性别变化（p = 0.425）。平均有效阻尼为314±72 Ns/m，有效躯干质量为37.0±9.3 kg。我们得出结论，应使用随机系统识别技术来计算有效躯干僵硬度和动力学特性。
