Quantitative assessment of trunk muscle coactivation in sub-maximal isometric exertion tasks

Abstract

This study empirically quantified the antagonistic moment induced by antagonistic trunk muscles as well as the sum of antagonistic forces during isometric exertion tasks: flexion/extension, lateral bending left/right, and twisting clockwise/ counter-clockwise. Twelve male subjects performed isometric voluntary exertions gradually increasing to maximum efforts. EMG signals from 10 trunk muscles and exertion forces were collected and muscle forces and moments were predicted from an EMG-assisted model. Antagonistic moments were assessed at 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% MVE. Antagonistic coactivation was dependent on the magnitude and direction of the exertion moment (p<0.05). The magnitude of the antagonistic moment was high during twisting exertions of about 40% of the exertion moment, 24% during flexion, 23% during lateral bending, and 10% during extension. The sum of antagonist forces showed almost the same result with the antagonistic moment. Spinal load was also high during twisting exertions and antagonistic muscles accounted for about 23% of the total compression force. From these results, it can be concluded that high coactivation is required to stabilize the spinal region during twisting exertions and this results in high spinal loads.