Experimental and modeled estimates of the mechanical stability of the lumbar spine

This study used an EMG-assisted biomechanical model of the lumbar spine to estimate spine stability achieved prior to a sudden trunk-unloading event. This stability was compared to spine stiffness calculated from trunk kinematics measured after unloading. For both extension and lateral bending trials, initial spine stability level was shown to account for approximately 50% of variance in subsequently exhibited trunk stiffness. These results suggest that in addition to the mechanical stability level of the spine prior to sudden loading, the reflex response of the muscles immediately after loading determines the kinematic response of the trunk and subsequent likelihood of injury