SPINE LOADING AND PROBABILITY OF LOW-BACK DISORDER RISK AS A FUNCTIONOF BOX LOCATION ON A PALLET

It is widely believed that depalletizing operations in manufacturing a nd service environments substantially increase the risk of occupationa lly related low back disorders (LBDs). It has been established that th e weight of the box lifted off a pallet can affect the risk of occupat ionally related LED but few have considered the influence of the locat ion of the box on the pallet (region) when assessing risk. Thus, the o bjective of this study was to assess spinal loading characteristics an d the probability of high LED risk as a function of box weight and its location on the pallet. Ten experienced order selectors were recruite d from a local distribution center and were evaluated as they transfer red boxes of different weights (40, 50, and 60 lb) from six different locations (regions) of a pallet to a pallet jack. Workers were monitor ed for their trunk motion characteristics as well as the electromyogra phic (EMG) activity of ten trunk muscles as they performed the task. W orkplace factors as well as trunk kinematic and EMG information were u sed as inputs to: (1) a risk assessment model, and (2) an EMG-assisted model that was used to predict the three-dimensional spine loadings t hat occurred during the task. The results indicated that conditions wh ere 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 b ox. 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 increas ed spinal loading and risk probability as the moment increased. This e ffort has also facilitated our understanding as to why spine loading i ncreases under the various conditions studied in this experiment. Near ly all differences in spinal loading can be explained by a correspondi ng difference in coactivation of the trunk musculature. This in turn s ignificantly increases the synergistic forces supplied by each muscle to the spine and results in an increase in spinal loading. (C) 1997 Jo hn Wiley & Sons, Inc.