Spine loading and probability of low back disorder risk as a function of box location on a pallet

Abstract

It is widely believed that depalletizing operations in manufacturing and service environments substantially increase the risk of occupationally related low back disorders (LBDs). It has been established that the weight of the box lifted off a pallet can affect the risk of occupationally related LBD but few have considered the influence of the location of the box on the pallet (region) when assessing risk. Thus, the objective of this study was to assess spinal loading characteristics and the probability of high LBD risk as a function of box weight and its location on the pallet. Ten experienced order selectors were recruited from a local distribution center and were evaluated as they transferred boxes of different weights (40, 50, and 60 lb) from six different locations (regions) of a pallet to a pallet jack. Workers were monitored for their trunk motion characteristics as well as the electromyographic (EMG) activity of ten trunk muscles as they performed the task. Workplace factors as well as trunk kinematic and EMG information were used as inputs to: (1) a risk assessment model, and (2) an EMG-assisted model that was used to predict the three-dimensional spine loadings that occurred during the task. The results indicated that conditions where a worker must reach to a low level of the pallet increased spinal load and risk probability far more than changes in the weight of the box. Thus, spinal loads were significantly large in magnitude and would be expected to lead to an increase in low back disorders when workers lifted form the lowest layer of the pallet. The load moment was found to be strongly influenced by pallet region, which resulted in increased spinal loading and risk probability as the moment increased. This effort has also facilitated our understanding as to why spine loading increases under the various conditions studied in this experiment. Nearly all differences in spinal loading can be explained by a corresponding difference in coactivation of the trunk musculature. This in turn significantly increases the synergistic forces supplied by each muscle to the spine and results in an increase in spinal loading. © 1997 John Wiley & Sons, Inc.