The Effects of Expectation on Trunk Loading

Abstract

The literature has reported that there is a link between sudden unexpected load handling and the risk of a low back injury. It was hypothesized that sudden unexpected loads would create excessive forces upon the trunk due to the overcompensation of the trunk muscles. An experiment was performed to test this theory and quantify the degree of overcompensation. Subjects were asked to hold a box in a static lift position while weights ranging from 5 to 20 pounds were dropped into the box from a constant height. Under some conditions (expected) the subjects were permitted to observe the weight drop while under other conditions (unexpected) the subjects were deprived of visual and auditory cues during the weight drop. Generally, it was found that during sudden unexpected loading the trunk response resembled an expected loading of twice the weight value. These findings may provide guidelines for work situations where unexpected loading conditions are common.