EVALUATION OF SPINAL LOADING DURING LOWERING AND LIFTING

Objective. To estimate the three-dimensional spinal loads during vario us lifting and lowering tasks. Design. The in vivo measurements of the trunk dynamics, moments, and myoelectric activity were used as inputs into an electromyographic-assisted model used to predict the three-di mensional spinal loads. Background. Previous studies of eccentric moti ons have investigated muscle activity, trunk strength, and trunk momen ts. A void in the body of knowledge exists in that none of these studi es investigated spinal loading. Methods. Ten subjects lifted (40 degre es of flexion to 0 degrees) and lowered (0 degrees of flexion to 40 de grees) boxes while positioned in a structure that restrained the pelvi s and hips. The tasks were performed under isokinetic trunk velocities of 5, 10, 20, 40, and 80 deg s(-1) while holding a box with weights o f 9.1, 18.2, and 27.3 kg. Results. Lowering strength was found to be 5 6% greater than lifting strength. The lowering tasks produced signific antly higher compression forces but lower anterior-posterior shear for ces than the lifting tasks. The differences in the spinal loads produc ed by the two lifting tasks were attributed to differences in coactivi ty and unequal lifting moments (i.e. holding the box farther away from the body). Conclusions. The nature of the spinal loads that occur dur ing lowering and lifting were significantly different. The difference in spinal loads may be explained by different lifting styles. Relevanc e This study revealed the importance of investigating lowering as well as lifting since these types of motions result in drastically differe nt EMG-torque relationships and, ultimately, different spinal loading patterns. Furthermore, this study indicates the importance of taking i nto account differences in lifting style (trunk moments) and the coact ivity of the trunk muscles when estimating loads on the spine. (C) 199 8 Elsevier Science Ltd. All rights reserved.