Gagnon M, Smyth G
Department of Physical Education, University of Montreal, Québec, Canada.
Ergonomics. 1992 Mar;35(3):329-45. doi: 10.1080/00140139208967817.
Whatever the lifting method used, dynamic factors appear to have an effect on the safe realization of movement, and NIOSH guidelines recommend smooth lifting with no sudden acceleration effects. On the other hand, inertial forces may play an important role in the process of transfer of momentum to the load. The direction by which these inertial forces may affect the loadings on body structures and processes of energy transfers cannot be determined a priori. A biomechanical experiment was performed to examine if there were differences in the execution processes between a slow-continuous lift and an accelerated-continuous lift, and also between accelerated lifts either executed continuously or interrupted with a pause. The lifts were executed from a height of 15 cm to a height of 185 cm above the head and with two different loads (6.4 and 11.6 kg). Five experienced workers in manual materials handling were used as subjects. Films and force platforms recordings supplied the data; dynamic segmental analyses were performed to calculate net muscular moments at each joint; a planar single-muscle equivalent was used to estimate compression loadings at L5/S1; total mechanical work, joint work distribution, and energy transfers were determined from a kinetic approach based on the integration of joint power as a function of time. Analyses of variance with repeated measures were applied to the three treatments. The results showed that joint muscular moments, spinal loadings, mechanical work, and muscular utilization ratios were generally increased by the presence of acceleration without inducing benefits of improved energy transfers; therefore slower lifts with reduced acceleration may be safer when handling moderately heavy loads. The maximum values of kinematic and kinetic factors were generally not affected by the pause, but the occurrence of jerks in the movement (acceleration, ground forces, and muscular moments) suggests that the pause may not be indicated when considering total exposure to muscular exertion. Full consideration should be given to the dynamics of motion when assessing risk factors in working tasks.
无论采用何种提升方法，动态因素似乎都会对安全实现动作产生影响，美国国家职业安全与健康研究所（NIOSH）的指南建议平稳提升，避免突然加速。另一方面，惯性力在将动量传递给负载的过程中可能起重要作用。这些惯性力影响身体结构上的负荷以及能量传递过程的方向无法预先确定。进行了一项生物力学实验，以检验缓慢连续提升和加速连续提升之间，以及连续执行或有停顿的加速提升之间在执行过程中是否存在差异。提升动作是从头部上方15厘米的高度提升到185厘米的高度，并使用两种不同的负载（6.4千克和11.6千克）。五名有经验的人工搬运材料的工人作为受试者。通过拍摄影片和力平台记录来提供数据；进行动态节段分析以计算每个关节处的净肌肉力矩；使用平面单肌肉等效模型来估计L5/S1处的压缩负荷；基于关节功率随时间的积分，从动力学方法确定总机械功、关节功分布和能量传递。对这三种处理应用重复测量方差分析。结果表明，加速的存在通常会增加关节肌肉力矩、脊柱负荷、机械功和肌肉利用率，但并未带来能量传递改善的益处；因此，在搬运中等重量的负载时，加速度较小的较慢提升可能更安全。运动学和动力学因素的最大值通常不受停顿的影响，但运动中急动的出现（加速度、地面力和肌肉力矩）表明，在考虑肌肉用力的总暴露量时，停顿可能并不合适。在评估工作任务中的风险因素时，应充分考虑运动的动力学。
