Toussaint H M, de Winter A F, de Haas Y, de Looze M P, Van Dieën J H, Kingma I
Department of Health Science, Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands.
J Biomech. 1995 Feb;28(2):199-210. doi: 10.1016/0021-9290(94)00051-5.
During the full flexion phase of the back lift movement the lumbar part of the erector spinae muscle exhibits a reduced activity level (flexion relaxation). This study addresses the question how the required extension torque in the lumbo-sacral joint (L5/S1 joint) is balanced during the period in which apparently the lumbar erector spinae ceases to take its share. Six subjects participated in the experiment in which they performed seven lifting tasks. The load, the range of movement, and the phase in which the load was handled (lifting or lowering) were varied. A dynamic linked segment model was applied to determine the momentary torques acting at the L5/S1 joint, while the EMGs of the lumbar and thoracic part of the erector spinae muscle were measured. Furthermore, the lengths between markers on the lumbar and thoracic part of the trunk were determined to reveal changes in length during the movement. The dynamic EMGs were normalized to trunk angle-dependent maximal levels. The L5/S1 joint torques were analysed and combined with the normalized EMG data and the kinematics of the trunk, which are assumed to indicate the elongation of passive tissues. Although in the normalization procedure the change of the length-force relationship of the erector spinae was taken into account, the dynamic lumbar EMG activity decreased to a low-activity level (the phenomenon of flexion relaxation). This coincided with a 25% increase in lumbar length suggesting that passive tissue strain provided part of the required extension torque. In the tasks where a barbell was handled a significant increase in EMG level of the thoracic part of the erector spinae occurred just before the flexion relaxation at the lumbar level. Apparently, the extensor function of the lumbar part is then taken over by the thoracic part of the erector spinae muscle. This suggests that an intricate coordinating mechanism is operative that apportions the load to be balanced over active--(lumbar and thoracic part of the erector spinae) and passive structures (post vertebral ligaments).
在背部上抬动作的完全屈曲阶段，竖脊肌的腰部部分表现出活动水平降低（屈曲放松）。本研究探讨了在腰椎竖脊肌明显不再发挥作用的期间，腰骶关节（L5/S1关节）所需的伸展扭矩是如何平衡的问题。六名受试者参与了实验，他们完成了七项举重任务。负荷、运动范围以及处理负荷的阶段（举起或放下）均有所变化。应用动态链接节段模型来确定作用于L5/S1关节的瞬间扭矩，同时测量竖脊肌腰部和胸部部分的肌电图。此外，还确定了躯干腰部和胸部部分标记物之间的长度，以揭示运动过程中的长度变化。将动态肌电图标准化为与躯干角度相关的最大水平。对L5/S1关节扭矩进行了分析，并与标准化的肌电图数据以及躯干的运动学数据相结合，这些数据被认为可指示被动组织的伸长情况。尽管在标准化过程中考虑了竖脊肌长度 - 力关系的变化，但动态腰部肌电图活动仍降至低活动水平（屈曲放松现象）。这与腰部长度增加25%相吻合，表明被动组织应变提供了部分所需的伸展扭矩。在处理杠铃的任务中，就在腰部水平出现屈曲放松之前，竖脊肌胸部部分的肌电图水平显著增加。显然，此时竖脊肌腰部部分的伸展功能由其胸部部分接管。这表明存在一种复杂的协调机制在起作用，该机制将需要平衡的负荷分配到主动结构（竖脊肌的腰部和胸部部分）和被动结构（椎后韧带）上。
