Assessment of Muscle Activity and Spine Compression during Constricted Axial Loading

Occupational-related low back disorders are the leading cause of lost work days as well as the most costly occupational safety and health problem facing industry today. Twisting has been found to be associated with lower back pain (Frymoyer, 1983). Previous biomechanical measures of twisting allowed ancillary moments and forces in addition to the twisting exertion. This confounding makes it difficult to assess twisting. However, pure twisting adds neuromuscular constraints. Research suggests optimal control strategy allows variability in redundant or task-irrelevant directions (Todorov, 2002). This suggests control of ancillary degrees of freedom (sagittal and lateral moment during twist exertion) may require increase motor control effort and muscle co-contraction. Therefore, the goal of this study was to compare muscle activity of the lumbar spine during pure twisting with less constricted twisting. The term pure twisting refers to a situation where the lateral and sagittal forces are no more than 20% of the axial torque. We hypothesize that muscle activity will be greater during constrictive twisting when compared to less constrained twisting.