THE INFLUENCE OF ACTUATION MODELING ON THE ASSESSED JOINT REACTIONS IN BIOMECHANICAL SYSTEMS

Introduction. Human body biomechanical models are actuated either by net torques at the joints or individual muscle forces whose action around the joints results, by principle, in the net torques. In the model-based inverse dynamics simulation of human movements the assessed joint reactions depend substantially on the choice of the actuation model, which is discussed in the paper. Material and methods. Using the two actuation models, variant biomechanical models of the lower limb, decomposed from the whole human body, were developed. They were then used for the inverse dynamics simulation of a recorded one-leg jump on the force platform to assess time variations of controls (either net torques or muscle forces) and joint reactions. Results. The assessed joint reactions obtained using the model actuated by net torques are substantially different from those obtained by means of the model actuated by muscle forces. Conclusion. The joint reactions computed using the model actuated by net torques do not involve contribution of the tensile muscle forces to the internal loads, and they are therefore underestimated. Determination of joint reactions should thus be based on musculoskeletal models actuated by the muscle forces.