Callaghan J P, McGill S M
Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, Ontario, Canada.
Spine (Phila Pa 1976). 1995 May 1;20(9):992-8. doi: 10.1097/00007632-199505000-00003.
This study analyzed anatomic and neural control characteristics of the trunk musculature. Subjects were exposed to external shear and compressive loads with equivalent moments to evaluate activation patterns and loading on the low back.
The migration of activity between the thoracic and lumbar erector spinae muscle groups was examined to determine whether the motor control system chooses to minimize joint loading by recognizing differences in moment, compression, and shear support requirements and assigning muscle activation in the most appropriate way.
Loads were applied either parallel or perpendicular to the low back to create compressive or shear forces. No previous study has attempted to isolate the response of the trunk musculature with the type of external load.
Eleven male subjects isometrically held an external load that was altered to create either a compressive or an anterior shear load on the low back but with equal extensor (reaction) moments (experiment 1). In a second experiment four men repeated the task with an increased range of applied loads (5-25 kg) together with measurements of intra-abdominal pressure.
The tasks with a compressive external load resulted in significantly higher levels of activation for all seven electromyographic channels recorded. Intraabdominal pressure, compressive and shear joint forces were all higher in the compression loading method when equal loads and low back moments were compared.
It was concluded that the motor control system does not arrange muscle activation levels in a way to minimize lumbar spinal loading at least for the relatively low levels of this study. Biomechanical models that use the objective criterion of minimum joint load may not be representative of the motor control system, at least in the low back.
本研究分析了躯干肌肉组织的解剖学和神经控制特征。让受试者承受具有等效力矩的外部剪切力和压缩力，以评估下背部的激活模式和负荷情况。
研究胸段和腰段竖脊肌群之间的活动迁移情况，以确定运动控制系统是否通过识别力矩、压缩和剪切支撑需求的差异，并以最合适的方式分配肌肉激活，来选择将关节负荷降至最低。
将负荷平行或垂直施加于下背部，以产生压缩力或剪切力。此前尚无研究尝试分离躯干肌肉组织对外加载荷类型的反应。
11名男性受试者等长保持一个外部负荷，该负荷经过改变，以便在下背部产生压缩负荷或前剪切负荷，但伸肌（反应）力矩相等（实验1）。在第二个实验中，4名男性重复该任务，施加的负荷范围增加（5 - 25千克），同时测量腹内压。
对于所记录的所有7个肌电图通道，施加压缩外部负荷的任务导致显著更高的激活水平。当比较相等负荷和下背部力矩时，压缩负荷方法中的腹内压、压缩和剪切关节力均更高。
得出的结论是，至少对于本研究中相对较低的负荷水平，运动控制系统不会以将腰椎负荷降至最低的方式安排肌肉激活水平。使用最小关节负荷这一客观标准的生物力学模型可能无法代表运动控制系统，至少在下背部是这样。
