Shin Gwanseob, Mirka Gary A
Department of Industrial and Systems Engineering, University at Buffalo, State University of New York, 415 Bell Hall, Buffalo, NY 14260, USA.
Clin Biomech (Bristol). 2007 Nov;22(9):965-71. doi: 10.1016/j.clinbiomech.2007.06.003. Epub 2007 Aug 20.
Full flexion lumbar postures maintained over a prolonged period of time have been shown to lead to changes in the supporting passive structures of the spine and it has been hypothesized that this may lead to low back pain/disorders. However, the specific biomechanics and physiology of this link have not been fully developed. Of particular interest is the interplay between the active and passive extensor mechanisms and the role of rest break in this response.
Ten healthy participants performed a regimen of a 10-min full lumbar flexion followed by a 10-min upright standing, with a slow speed isokinetic lift every 2.5min. Changes in the full lumbar flexion angle (system creep) and the electromyographic activity of back extensors in the isokinetic lifts were evaluated.
Results showed significant increases in the full flexion angle and increased activity of the extensor muscles in the prolonged flexion to compensate for the reduced extension moment producing capability of the passive tissues. A 30-s rest break in the middle of the flexion moderated these viscoelastic responses.
The results suggest that prolonged lumbar flexion results in the systematic transfer of an extension moment from passive tissues to active muscles. Heavy lifting or high force exertion of back muscles immediately after prolonged flexion could be a risk factor for low back disorders when the muscles lose their force generating capacity due to passive stretching. This study also indicated the importance of sufficient rest between consecutive full flexion tasks in reducing the risk.
长时间保持腰椎完全屈曲姿势已被证明会导致脊柱支撑性被动结构发生变化，据推测这可能会导致腰痛/疾病。然而，这种联系的具体生物力学和生理学机制尚未完全阐明。特别值得关注的是主动和被动伸肌机制之间的相互作用以及休息中断在这种反应中的作用。
10名健康参与者进行了一个方案，即先进行10分钟的腰椎完全屈曲，然后站立10分钟，每2.5分钟进行一次慢速等速提升。评估了等速提升过程中腰椎完全屈曲角度（系统蠕变）和背部伸肌的肌电图活动变化。
结果显示，在长时间屈曲过程中，完全屈曲角度显著增加，伸肌活动增强，以补偿被动组织伸展力矩产生能力的下降。在屈曲过程中间进行30秒的休息可减轻这些粘弹性反应。
结果表明，长时间的腰椎屈曲会导致伸展力矩从被动组织系统地转移到主动肌肉。当肌肉因被动拉伸而失去力量产生能力时，如果在长时间屈曲后立即进行重物提升或强力使用背部肌肉，可能是导致腰部疾病的一个危险因素。这项研究还表明，在连续的完全屈曲任务之间进行充分休息对于降低风险很重要。
