Howarth Samuel J, Beach Tyson A C, Pearson Adam J, Callaghan Jack P
Faculty of Applied Health Sciences, Department of Kinesiology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
Appl Ergon. 2009 May;40(3):433-9. doi: 10.1016/j.apergo.2008.10.006. Epub 2008 Dec 10.
Workers are often required to perform manual materials handling tasks immediately following periods of prolonged sitting either as a secondary job component of as different tasks in a job rotation strategy. The goal of this investigation was to determine if changes to low-back kinetics and/or kinematics occurred during repetitive lifting/lowering exertions following extended seated exposures. Upper body kinematics, lumbar spine flexion angle, pelvic orientation and bilateral muscle activity from the external abdominal obliques and lumbar erector spinae were recorded for 8 males and 8 females while they alternated between sessions of repetitive lifting/lowering and prolonged sitting. Upper body kinematics were used as inputs to a linked segment model to compute low-back flexion/extension moments, compression, and shear. Peak lumbar flexion was reduced by 1.8 degrees during the lifting/lowering exertions following the first hour of sitting which consequently led to a reduction of approximately 50N in the reaction anteroposterior shear forces. Sitting postures were consistent with previously reported data. The reduced shear loads during repetitive lift/lower exertions following prolonged sitting may be a consequence of alterations in passive tissue properties which could alter the risk of low-back injury, although future research is required to examine the biomechanical significance of this finding. Changes to both kinematics and kinetics were minimal suggesting that using prolonged sitting as a component of a task series in job rotation does not alter the risk present when combined with repetitive lifting tasks.
工人经常被要求在长时间坐着之后立即执行手工物料搬运任务，这要么是作为工作轮换策略中不同任务的次要工作组成部分。本研究的目的是确定在长时间坐着后进行重复性提举/放下用力时，下背部动力学和/或运动学是否发生变化。在8名男性和8名女性交替进行重复性提举/放下和长时间坐着的过程中，记录了他们的上身运动学、腰椎前屈角度、骨盆方向以及腹外斜肌和竖脊肌的双侧肌肉活动。上身运动学被用作链接节段模型的输入，以计算下背部的屈伸力矩、压缩力和剪切力。在坐了第一个小时后的提举/放下用力过程中，腰椎最大前屈角度减小了1.8度，这导致反应前后剪切力减少了约50N。坐姿与先前报道的数据一致。长时间坐着后进行重复性提举/放下用力时剪切负荷的降低可能是被动组织特性改变的结果，这可能会改变下背部受伤的风险，不过需要进一步的研究来检验这一发现的生物力学意义。运动学和动力学的变化都很小，这表明在工作轮换中将长时间坐着作为任务系列的一个组成部分，与重复性提举任务相结合时，不会改变存在的风险。
