Marras W S, Granata K P
Biodynamics Laboratory, Ohio State University, Columbus, USA.
Spine (Phila Pa 1976). 1995 Jul 1;20(13):1440-51. doi: 10.1097/00007632-199507000-00002.
Measured trunk kinematics, applied moments, and trunk muscle activities were employed in a biomechanical model to determine load experiences by the spine during dynamic torsional exertions.
The purpose of this investigation was to examine the influence of dynamic twisting parameters on spinal load.
Axial twisting of the torso has been identified as a significant risk factor for occupationally related low back disorders. However, previous studies have had difficulty describing how twisting is accomplished biomechanically, or how the spine is loaded during twisting motions.
Electromyograph activity of 10 trunk muscles was monitored while 12 subjects performed twisting exertions under various conditions of force, velocity, position, and direction. An electromyograph-assisted biomechanical model was developed to interpret the effects of those twisting parameters on spine loading.
Significant flexion-extension and lateral moments were generated during the twisting exertions. Muscle co-activity associated with twisting exertions was significantly greater than that associated with lifting exertions. Employing electromyograph data to represent muscle co-activity, the model accurately predicted trunk moments and hence was assumed to reasonably reflect spine loading.
Under the conditions tested, the results indicated that relative spinal compression during dynamic twisting exertions was twice that of static exertions. Spine loading also varied as a function of whether the trunk was twisted to the left or right and according to the direction of applied torsion--i.e., clockwise or counterclockwise. The results may help explain, biomechanically, why epidemiologic findings have repeatedly identified twisting as a risk factor for low back disorder.
在生物力学模型中采用测量的躯干运动学、施加的力矩和躯干肌肉活动，以确定动态扭转用力时脊柱所承受的负荷。
本研究的目的是检验动态扭转参数对脊柱负荷的影响。
躯干的轴向扭转已被确定为职业性下背痛的一个重要危险因素。然而，以往的研究难以描述扭转是如何通过生物力学方式完成的，或者在扭转运动过程中脊柱是如何承受负荷的。
在12名受试者于不同力、速度、位置和方向条件下进行扭转用力时，监测10块躯干肌肉的肌电图活动。开发了一个肌电图辅助生物力学模型，以解释这些扭转参数对脊柱负荷的影响。
扭转用力时产生了显著的屈伸和侧方力矩。与扭转用力相关的肌肉协同活动显著大于与提举用力相关的肌肉协同活动。利用肌电图数据来表示肌肉协同活动，该模型准确地预测了躯干力矩，因此被认为能合理反映脊柱负荷。
在测试条件下，结果表明动态扭转用力时的相对脊柱压缩是静态用力时的两倍。脊柱负荷还因躯干向左或向右扭转以及所施加扭转的方向（即顺时针或逆时针）而有所不同。这些结果可能有助于从生物力学角度解释为什么流行病学研究结果一再将扭转确定为下背痛的一个危险因素。
