Application of a Kinematics-Driven Approach in Human Spine Biomechanics During an Isometric Lift

Abstract

Effective prevention and treatment management of spinal disorders can only be based on accurate estimation of muscle forces and spinal loads during various activities such as lifting. The infeasibility of experimental methods to measure muscle and spinal loads has prompted the use of biomechanical modeling techniques. A major shortcoming in many previous and current models is the consideration of equilibrium conditions only at a single cross section, rather than along the entire length of the spine, when attempting to compute muscle forces and spinal loads. The assumption of extensor global muscles with straight rather than curved paths and of the spinal segments as joints with no translational degrees-of-freedom, are additional issues that need to be critically evaluated when simulating lifting tasks. The kinematics-driven approach, which satisfies equilibrium conditions in all spinal directions and levels and yields spinal postures compatible with external loads, muscle forces and nonlinear passive properties, while also taking into account the wrapping of trunk muscles, is employed. Results demonstrate that, regardless of the method used (optimization or EMG-assisted), single-level free body diagram models yield estimations that grossly violate equilibrium at other levels. The computed results are also markedly level-dependent. The crucial effects of the proper consideration of global muscles with curved paths and of spinal segments with translational degrees-of-freedom when attempting to estimate muscle forces and spinal loads in isometric lifting tasks are also demonstrated.