Reduction of spinal loading through the use of handles

A study was performed to investigate how different types of handle coupling affect the loading on the spine. Ten male grocery item selectors performed a laboratory simulation of a warehouse palletizing task. Participants transferred the cases from a pallet in a storage bin to the destination pallet. The trunk motions and muscle activities were monitored by a Lumbar Motion Monitor (LMM) and electromyographic electrodes, respectively, and used as input to an EMG-assisted biomechanical model. The results of the study revealed that the presence of handles reduced the complex loads on the spine. This was particuarly true when lifting to the lowest positions of the pallet, where the highest forces occurred. It was determined that the maximum spinal compression forces were reduced by an average of 6.8% when handles were added to the cases. The presence of handles affected the moments imposed on the trunk in the lower regions on the pallet, indicating a difference in lifting style and/or more sagittal flexion. The results of this study suggest that the multiplier for handle coupling in the 1991 NIOSH Revised Lifting Equation was appropriate for higher lifts (at 133.8 cm), but needs to be more protective for 'poor' coupling conditions with lower vertical heights, which are the most common in industry. Based on these results, it is recommended that handles be designed into the cases that are commonly lifted from low levels in warehousing and other manual materials handling situations.