Development of a multibody biomechanical model of the human upper limb

This chapter aims to describe step by step the development of a novel explicit biomechanical multibody model, proposed by the same authors as a previous research result. The model allows solving the inverse dynamics problems of upper limb musculoskeletal systems, with the purpose to evaluate joint reactions due to known kinematics, accounting for the muscular activations. The model was developed by using a classical multibody approach, and it was based on the constraint kinematical behaviour analysis. It considers both the linear and the curved muscle model, obtained by calculating the geodesic muscle path over wrapping surfaces. The Hill muscle model was adopted to evaluate the contractile elements' actions and the passive ones. The obtained equations were solved in Matlab code and the calculated results were verified with those obtained by a commercial software, by using input kinematical data referred to an upper limb subjected to gravity external forces and a simply imposed kinematics (OpenSim "arm26" folder). As showed, the obtained results match very satisfactory the calculations obtained by the commercial software in terms of kinematical analysis, driving forces, muscles' activations and joint reactions, allowing the Authors to conclude that the proposed explicit model should be used as a computational tool for biomechanical simulations of the upper limb, and also for the calculation of the joint reactions which are very useful in artificial joint structural and tribological design.