Low-back stresses when learning to use a materials handling device

This study examines the potential effect of short-term practice on low-back stresses during manual lifting and lowering of a 15 kg load, and while usi ng two different types of materials handling devices (MHDs) to lift and low er a 40 kg load. The two MHDs used were an articulated balance arm and a pn eumatic hoist. The expectation was that low-back dynamic moments, EMG measu red torso muscle antagonism, and EMG predicted L4/L5 disc compression force s would rapidly decrease with practice, and that the manual lift-lower acti vities would be learned faster than the MHD-assisted exertions. Four naive male college age subjects performed 40 lift and lower exertions, both manua lly and with the two MHDs for a total of 24 experiments. Non-linear regress ions of the peak and average low-back moments, EMGs and disc compression va lues revealed only small decreases in the values (from 2 to 14%) over the 4 0 trials, and it was only statistically significant for five of the 48 regr essions. This would seem to indicate that if learning is present in these t asks it is going to be very slow learning, and thus future studies will nee d to include a much larger number of trials. The effects of MHDs on the lea rning rates when compared to manual lifting learning rates was not statisti cally significant. It was shown, however, that MHDs had a particularly bene ficial effect on reducing L4/L5 compression forces during load lowering act ivities despite the MHD load being much heavier than the manual load. It al so was found that the level of torso muscle co-contraction increased signif icantly (2-4 times) when MHD handling was involved compared to manual lifti ng and lowering.