STABILITY OF MUSCULAR LOADING OF THE LUMBAR SPINE

肌肉僵硬和脊柱运动节段僵硬的组合保护腰椎免受屈曲失稳的可能性。这是一个应用程序，用于支持(R01 AR 44119)的持续研究，分析和量化在各种负荷条件和脊柱姿势下稳定所需的肌肉僵硬程度。以前的分析预测，拮抗性肌肉激活将增加稳定性，这种拮抗活性的存在已经在肌电记录的肌肉激活的实验研究中得到证实。总体的假设是，肌肉控制受损可能使腰椎更容易发生损伤性屈曲。拟议的后续研究将集中在四个主要方面的工作：(1)人体实验，以表征在逐渐增加的努力和扰动负荷条件下的肌肉激活模式，并测量躯干的驱动点硬度，由此推导出不同激活条件下的肌肉硬度；(2)在轴向压缩载荷和周围流体介质的生理条件下，对腰椎运动节段(有和没有完整的后部元件)的硬度进行实验量化。(3将使用新的分析模型进行这些实验的模拟，该模型计算优化五个成本函数组件的可变组合所需的肌肉激活模式，即脊柱的全局运动、椎间位移、椎间运动片段的负载、立方肌肉应力和稳定性的总和(通过系统刚度的特征值的大小)。来自人体受试者和运动片段研究的一些实验数据将用于为模型中的参数赋值，其他数据将用于验证模型。(4)对间歇性下腰痛受试者的肌肉功能的纵向研究将表明这些个体是否有有利于脊柱不稳定的肌肉激活行为。这些研究将有助于确定肌肉僵硬和脊柱僵硬在稳定脊柱方面的相对作用。他们将确定以下情况：(1)运动节段僵硬减少，(2)肌肉僵硬减少，或(3)肌肉招募模式异常，在表面上良性的外部负荷条件下，腰椎有可能发生自损性屈曲发作。此外，个别肌肉的具体作用将被更好地阐明，这将有助于指导下腰功能障碍患者的治疗。

A combination of muscle stiffness and spinal motion segment stiffness protect the lumbar spine against the possibility of buckling instabilities. This is an application to support continued research (of R01 AR 44119) analyzing and quantifying the degree of muscle stiffness required for stability under a variety of loading conditions and spinal postures. Previous analyses have predicted that antagonistic muscle activation would increase stability, and the existence of such antagonistic activity has been confirmed in experimental studies documenting muscle activation electromyographically. The overall hypothesis is that impaired muscular control might predispose the lumbar spine to injurious buckling episodes. The proposed continuation studies will focus on four main areas of work: (1) human subject experiments to characterize muscle activation patterns under gradually increasing efforts and under perturbed loading conditions, and to measure driving point stiffness of the trunk, from which muscle stiffness will be deduced under differing activation conditions; (2) Experimental quantification of the stiffness of lumbar spinal motion segments (with and without intact posterior elements) under physiological conditions of axial compressive loading and surrounding fluid medium. (3 Simulations of these experiments will be performed using a new analytical model which calculates the muscle activation pattern required to optimize a variable combination of five cost function components, namely the global motion of the spine, intervertebral displacements, loading of intervertebral motion segments, the sum of cubed muscle stress and stability (via the magnitude of eigenvalues of the system stiffness). Some of the experimental data from human subject and motion segment studies will be used to assign values to parameters in the model, other data will be used to validate the model. (4) Longitudinal studies of muscle function in subjects with intermittent low back pain will indicate whether these individuals have muscle activation behaviors conducive to spinal instability. These studies will help to define the relative roles of muscle stiffness and spinal stiffness in stabilizing the spinal column. They will identify the conditions under which (1) reduced motion segment stiffness, (2) reduced muscular stiffness or (3) abnormal patterns of muscle recruitment might place the lumbar spine at risk for self-injurious buckling episodes under apparently benign external loading conditions. In addition, the specific roles of individual muscles will be better elucidated, which will be helpful in guiding therapy for people with low back dysfunction.