The load distribution among lumbar spinal structures-still an unanswered question-has been in the focus of this hybrid experimental and simulation study. First, the overall passive resistive torque-angle characteristics of healthy subjects' lumbar spines during flexion-extension cycles in the sagittal plane were determined experimentally by use of a custom-made trunk-bending machine. Second, a forward dynamic computer model of the human body that incorporates a detailed lumbar spine was used to (1) simulate the human-machine interaction in accordance with the experiments and (2) validate the modeled properties of the load-bearing structures. Third, the computer model was used to predict the load distribution in the experimental situation among the implemented lumbar spine structures: muscle-tendon units, ligaments, intervertebral discs, and facet joints. Nine female and 10 male volunteers were investigated. Lumbar kinematics were measured with a marker-based infrared device. The lumbar flexion resistance was measured by the trunk-bending machine through strain gauges on the axes of the machine's torque motors. Any lumbar muscle activity was excluded by simultaneous sEMG monitoring. A mathematical model was used to describe the nonlinear flexion characteristics. The subsequent extension branch of a flexion-extension torque-angle characteristic could be significantly distinguished from its flexion branch by the zero-torque lordosis angle shifted to lower values. A side finding was that the model values of ligament and passive muscle stiffnesses, extracted from well-established literature sources, had to be distinctly reduced in order to approach our measured overall lumbar stiffness values. Even after such parameter adjustment, the computer model still predicts too stiff lumbar spines in most cases in comparison with experimental data. A review of literature data reveals a deficient documentation of anatomical and mechanical parameters of spinal ligaments. For instance, rest lengths of ligaments-a very sensitive parameter for simulations-and cross-sectional areas turned out to be documented at best incompletely. Yet by now, our model well reproduces the literature data of measured pressure values within the lumbar disc at level L4/5. Stretch of the lumbar dorsal (passive) muscle and ligament structures as an inescapable response to flexion can fully explain the pressure values in the lumbar disc. Any further external forces like gravity, or any muscle activities, further increase the compressive load on a vertebral disc. The impact of daily or sportive movements on the loads of the spinal structures other than the disc cannot be predicted ad hoc, because, for example, the load distribution itself crucially determines the structures' current lever arms. In summary, compressive loads on the vertebral discs are not the major determinants, and very likely also not the key indicators, of the load scenario in the lumbar spine. All other structures should be considered at least equally relevant in the future. Likewise, load indicators other than disc compression are advisable to turn attention to. Further, lumbar flexion is a self-contained factor of lumbar load. It may be worthwhile, to take more consciously care of trunk flexion during daily activities, for instance, regarding long-term effects like lasting repetitive flexions or sedentary postures.

中文翻译：

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负载在体内分布在被动弯曲的腰椎中的椎骨、肌肉、脊柱韧带和椎间盘之间。

腰椎结构之间的负荷分布——仍然是一个悬而未决的问题——一直是这项混合实验和模拟研究的重点。首先，通过使用定制的躯干弯曲机，通过实验确定健康受试者在矢状面屈伸循环期间的整体被动阻力扭矩角特性。其次，使用包含详细腰椎的人体前向动态计算机模型来 (1) 根据实验模拟人机交互，以及 (2) 验证承重结构的建模特性。第三，使用计算机模型来预测实验情况下实施的腰椎结构之间的负荷分布：肌腱单位、韧带、椎间盘、和小关节。调查了 9 名女性和 10 名男性志愿者。使用基于标记的红外设备测量腰椎运动学。腰椎屈曲阻力是由躯干弯曲机通过机器扭矩电机轴上的应变仪测量的。通过同步 sEMG 监测排除任何腰肌活动。使用数学模型来描述非线性屈曲特性。屈曲-伸展扭矩-角度特性的后续伸展分支可以通过将零扭矩前凸角移至较低值而与其屈曲分支显着区分开来。一个附带发现是韧带和被动肌肉僵硬的模型值，从完善的文献来源中提取，为了接近我们测量的整体腰椎刚度值，必须明显减少。即使经过这样的参数调整，与实验数据相比，计算机模型在大多数情况下仍然预测腰椎过于僵硬。对文献数据的回顾揭示了对脊柱韧带解剖和机械参数的缺乏记录。例如，韧带的静止长度 - 一个非常敏感的模拟参数 - 和横截面积被证明充其量只是不完整的记录。然而到目前为止，我们的模型很好地再现了 L4/5 级腰椎间盘内压力测量值的文献数据。腰背（被动）肌肉和韧带结构的伸展是对屈曲不可避免的反应，可以充分解释腰椎间盘的压力值。任何进一步的外力，如重力，或任何肌肉活动，进一步增加椎间盘的压缩负荷。日常或运动运动对除椎间盘以外的脊柱结构载荷的影响无法临时预测，因为例如，载荷分布本身至关重要地决定了结构的当前杠杆臂。总之，椎间盘上的压力负荷不是腰椎负荷情况的主要决定因素，也很可能不是关键指标。所有其他结构在未来至少应被视为具有同等相关性。同样，建议关注磁盘压缩以外的负载指标。此外，腰椎屈曲是腰椎负荷的一个独立因素。在日常活动中更有意识地注意躯干屈曲可能是值得的，例如，