Benefits of Trunk Muscle Co-Contraction in Protecting against Low-Back Injury during Manual Materials Lifting

There is a trade-off between the risk of low-back injury associated with tissue overload versus the risk of spinal instability. The benefit of antagonistic co-contraction in helping to prevent low-back pain associated with instability injury during manual materials handling tasks was examined. Ten healthy males performed sagittal lifting tasks while trunk motion, reaction loads, and EMG activity were recorded. A biomechanical model was developed to compute spinal load and spinal stability during the tasks. Antagonistic co-contraction was found to be beneficial in terms of the stability versus spinal load, i.e. compression increased 12–18% while stability increased 36–64%. Stability was a minimum at low trunk moments, e.g. upright postures. Conversely, as trunk moment increased the risk of stability failure was reduced but the risk of spinal tissue overload injury was increased. To compensate, subjects recruited antagonistic co-contraction less in high moment conditions and more in low moment conditions.