Arjmand N, Shirazi-Adl A, Bazrgari B
Division of Applied Mechanics, Department of Mechanical Engineering, Ecole Polytechnique, P.O. Box 6079, Station centre-ville, Montréal, Que., Canada H3C 3A7.
Clin Biomech (Bristol). 2006 Aug;21(7):668-75. doi: 10.1016/j.clinbiomech.2006.03.006. Epub 2006 May 6.
An improved assessment of risk of spinal injury during lifting activities depends on an accurate estimation of trunk muscle forces, spinal loads and stability margin which in turn requires, amongst others, an accurate description of trunk muscle geometries. The lines of action of erector spinae muscles are often assumed to be linear despite the curved paths of these muscles in forward flexion postures.
A novel approach was introduced that allowed for the proper simulation of curved paths for global extensor muscles in our Kinematics-driven finite element model. The lever arms of global muscles at different levels were restrained either to remain the same or decrease only by 10% relative to their respective values in upright posture. Based on our earlier measurements, static lifting tasks at two trunk flexions (40 degrees and 65 degrees ) and three lumbar postures (free style, lordotic and kyphotic) with 180 N in hands were analyzed.
Muscle forces and spinal compression at all levels substantially decreased as the global extensor muscles took curved paths. In contrast, the shear force at lower levels increased. Allowing for a 10% reduction in these lever arms during flexion increased muscle forces and compression forces at all levels. Despite smaller muscle forces, wrapping of global muscles slightly improved the spinal stability.
Consideration of global extensor muscles with curved paths and realistic lever arms is important in biomechanical analysis of lifting tasks. Reduction in the erector spinae lever arms during flexion tasks could vary depending on the lumbar posture. Results advocate small flattening of the lumbar curvature in isometric lifts yielding smaller compression and shear forces at the critical L5-S1 level.
提升活动期间对脊柱损伤风险的改进评估取决于对躯干肌力、脊柱负荷和稳定裕度的准确估计，而这反过来又需要，除其他外，对躯干肌肉几何形状的准确描述。尽管竖脊肌在向前屈曲姿势中的路径是弯曲的，但通常假定其作用线是线性的。
引入了一种新方法，该方法允许在我们的运动学驱动有限元模型中对整体伸肌的弯曲路径进行适当模拟。不同水平的整体肌肉的力臂被限制为保持不变或相对于其在直立姿势下的各自值仅减小10%。基于我们早期的测量，分析了在两种躯干屈曲（40度和65度）和三种腰椎姿势（自由式、前凸和后凸）下手持180 N重物的静态提升任务。
随着整体伸肌采用弯曲路径，各级肌肉力和脊柱压缩力大幅下降。相比之下，较低水平的剪切力增加。在屈曲过程中允许这些力臂减小10%会增加各级的肌肉力和压缩力。尽管肌肉力较小，但整体肌肉的包裹略微改善了脊柱稳定性。
在提升任务的生物力学分析中，考虑具有弯曲路径和实际力臂的整体伸肌很重要。屈曲任务期间竖脊肌力臂的减小可能因腰椎姿势而异。结果表明，在等长提升中腰椎曲率略有变平会在关键的L5-S1水平产生较小的压缩力和剪切力。
