Disturbance and recovery of trunk stiffness and reflexive muscle responses following prolonged trunk flexion: Influences of flexion angle and duration
Disturbance and recovery of trunk stiffness and reflexive muscle responses following prolonged trunk flexion: Influences of flexion angle and duration
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DOI：
10.1016/j.clinbiomech.2010.09.019
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发表时间：
2011-03-01
影响因子：
1.8
通讯作者：
Madigan, Michael L.
中科院分区：
文献类型：
--
作者：
Hendershot, Brad;Bazrgari, Babak;Madigan, Michael L.
背景：实验研究表明，弯曲的工作姿势减少了脊柱的被动支撑，这可能是职业性腰背部疾病发展的一个重要危险因素。减少被动僵硬的神经肌肉代偿包括基线活动或躯干肌肉反射性激活的增加。然而，人类长时间屈曲后主动和被动组织之间的协同作用的改变和恢复目前尚不清楚。方法：12名健康参与者暴露于两种躯干屈曲持续时间（2和16分钟）和三种屈曲角度（33、66和100%的个人屈曲松弛角度）的所有组合。在整个暴露过程中记录负荷松弛，而在对突然扰动的动态反应中研究腰伸肌的躯干刚度和反射行为。结果：载荷松弛程度随屈曲角度的增加而增加。屈曲暴露后躯干刚度降低，反射增益增加；对于这两种结果，暴露于增加屈曲角度后的急性变化更大。暴露于最大屈曲后一小时，反射增益仍然升高。解释：暴露于长时间的躯干弯曲改变了躯干僵硬和反射行为，其模式与流行病学证据一致，将这种暴露与职业性腰背部疾病的风险联系起来。观察到的反射增益的增加，至少在健康个体中，可能是对急性暴露于屈曲姿势后被动躯干僵硬减少的补偿。神经肌肉系统是否能对暴露于重复屈曲任务后被动结构中累积的干扰作出类似的反应仍有待确定。(c) 2010 Elsevier Ltd.版权所有。
Background: Experimental studies suggest that flexed working postures reduce passive support of the spine, which could represent a significant risk factor for the development of occupational low back disorders. Neuromuscular compensations to reduced passive stiffness include increases in baseline activity or reflexive activation of trunk muscles. Yet, alterations and recovery of the synergy between active and passive tissues following prolonged flexion in humans are currently unknown.Methods: Twelve healthy participants were exposed to all combinations of two trunk flexion durations (2 and 16 min) and three flexion angles (33, 66, and 100% of individual flexion-relaxation angle). Load relaxation was recorded throughout exposures, whereas trunk stiffness and reflexive behaviors of the lumbar extensor muscles were investigated during dynamic responses to sudden perturbations.Findings: The magnitude of load relaxation increased with increasing flexion angle. Trunk stiffness decreased and reflex gains increased following flexion exposures; for both outcomes, acute changes were larger following exposure to increasing flexion angle. Reflex gains remained elevated one hour after exposure to maximum flexion.Interpretation: Exposure to prolonged trunk flexion changed trunk stiffness and reflex behavior in patterns consistent with epidemiological evidence linking such exposure with the risk of occupational low back disorders. Observed increases in reflex gains, at least among healthy individuals, may be a compensation for decreases in passive trunk stiffness following acute exposure to flexed postures. It remains to be determined whether the neuromuscular system can similarly respond to accumulated disturbances in passive structures following exposure to repeated flexion tasks. (c) 2010 Elsevier Ltd. All rights reserved.