Ning Xiaopeng, Haddad Omid, Jin Sangeun, Mirka Gary A
The Ergonomics Laboratory, Department of Industrial and Manufacturing Systems Engineering, Iowa State University, Ames, IA 50011-2164, USA.
Clin Biomech (Bristol). 2011 Jan;26(1):35-9. doi: 10.1016/j.clinbiomech.2010.08.012. Epub 2010 Oct 12.
the flexion relaxation phenomenon has been extensively studied in sagittally symmetric postures. Knowledge about this phenomenon in asymmetric trunk postures is less well understood, and may help to reveal the underlying physiology of the passive tissue/active tissue load-sharing mechanism in the lumbar region.
twelve participants performed fifteen controlled, full range trunk flexion-extension motions toward three asymmetric lifting postures (0° (sagittally symmetric), 15°, and 30° from the mid-sagittal plane). The electromyographic activity data from the paraspinals at the L3 and L4 levels and trunk kinematics data from motion sensors over the C7, T12 and S1 vertebrae were recorded. The lumbar flexion angles at which these muscles' activities were reduced to resting levels during forward flexion provided quantitative data describing the effects of asymmetry on the passive tissue/active tissue interaction.
flexion relaxation was observed in the muscles contralateral to the direction of the asymmetric trunk flexion motion. The response of the ipsilateral extensor musculature was much less consistent, with many trials indicating that flexion relaxation was never achieved. Increasing asymmetry from 0° to 30° led to a 10% reduction in the maximum lumbar flexion. Lumbar flexion angles necessary to achieve flexion relaxation in the contralateral muscles also decreased (L4 paraspinal-related angle decreasing by 15% and the L3 paraspinal-related angle decreasing by 21%).
under asymmetric conditions the lumbar flexion angle at which the transition from active muscle to passive ligamentous extension moment is altered from that seen in symmetric motions and this transition can have implications for the loading of the spine in full flexion (or near full flexion) postures.
屈曲放松现象已在矢状面对称姿势中得到广泛研究。关于该现象在不对称躯干姿势中的情况了解较少，这可能有助于揭示腰椎区域被动组织/主动组织负荷分担机制的潜在生理学原理。
12名参与者朝着三种不对称举重姿势（0°（矢状面对称）、偏离正中矢状面15°和30°）进行了15次受控的全范围躯干屈伸运动。记录了L3和L4水平椎旁肌的肌电图活动数据以及C7、T12和S1椎体上运动传感器的躯干运动学数据。在向前屈曲过程中这些肌肉活动降至静息水平时的腰椎屈曲角度提供了描述不对称对被动组织/主动组织相互作用影响的定量数据。
在不对称躯干屈曲运动方向对侧的肌肉中观察到了屈曲放松现象。同侧伸肌组织的反应则不太一致，许多试验表明从未实现屈曲放松。不对称程度从0°增加到30°导致最大腰椎屈曲减少10%。对侧肌肉实现屈曲放松所需的腰椎屈曲角度也减小（与L4椎旁肌相关的角度减小15%，与L3椎旁肌相关的角度减小21%）。
在不对称条件下，从主动肌肉到被动韧带伸展力矩转变时的腰椎屈曲角度与对称运动时不同，这种转变可能会影响脊柱在完全屈曲（或接近完全屈曲）姿势下的负荷。
