Transient analysis of trunk response in sudden release loading using kinematics-driven finite element model

Background: Sudden trunk perturbations occur in various occupational and sport activities. Despite numerous measurement studies, no comprehensive modeling simulations have yet been attempted to investigate trunk biodynamics under sudden loading/unloading. Methods: Dynamic kinematics-driven approach was used to evaluate the temporal variation of trunk muscle forces, internal loads and stability before and after a sudden release of a posterior horizontal load. Measured post-disturbance trunk kinematics, as input, and muscle electromyography (EMG) activities, for qualitative validation, were considered. Findings: Computed agonist and antagonist muscle forces before and after release agreed well with reported EMG activities and demonstrated basic response characteristics such as activation latency and reflex activation. The trunk was found quite stable before release and in early post-release period. Larger applied load substantially increased trunk kinematics, muscle forces and spinal loads. Interpretation: Excessive spinal loads due to large muscle forces in sudden loading conditions is a risk factor as the central nervous system attempts to reflexively control the sudden disturbances, a situation that further deteriorates under larger perturbations and longer latency periods. Predictions indicate the potential of the kinematics-driven model in ergonomics as well as training and rehabilitation programs.