Effect of Load Asymmetry on Internal Loading of the Trunk

摘要

The effects of changes in the magnitude and angle of the net resultant force onthe electromyographic (EMG) activity of trunk muscles, and the forces acting on the lumbar spine during upright asymmetric isometric trunk exertion were evaluated. The activities of ten trunk muscles were quantified using wire and surface EMG during maximal and submaximal isometric exertion. Subjects included 15 healthy volunteers, mean age 29.8 years. Muscle parameters were calculated from computed tomography images. The normalized root mean square (NRMS) EMG of the trunk muscles were affected by trunk movement magnitude and angle. An EMG driven model of lumbar spine load was used to calculate compression and shear forces. The author concludes that the selected trunk muscles were significantly affected by the magnitude and direction of the net resultant moment. The NRMS-EMG activity of the trunk muscles was magnitude and direction of the net resultant moment. The NRMS-EMG activity of the trunk muscles was magnitude and direction of the net resultant moment. The NRMS-EMG activity of the trunk muscles was higher during combined (asymmetric) isometric exertion compared to pure (symmetric) isometric trunk exertion. The controllability and capability of high magnitude trunk moments were significantly affected by the direction of the net resultant moment. The results may have special applications for ergonomic job evaluation and job design. The author recommends that repetitive tasks involving asymmetric trunk postures should be avoided as should the combination of lexion and twisting of the trunk.