Multibody model for the biomechanical analysis of the upper limb

In this paper a multibody model of the upper limb is presented. The limb is modelled as a three dimensional 7 degrees-of-freedom system, linked to the shoulder which has been considered as frame. The upper limb model is made up of four links corresponding to the most important body segments: the humerus, the ulna, the radius and the hand, considered as a single rigid body. Particular attention has been paid to the modelling of joints in order to mimic all the possible arm and forearm movements (including pronosupination) The model also includes 24 muscles. The mathematical model used to describe the muscles is those proposed by Zajac in 1989, modified by the authors. The kinematic analysis has been performed including an ergonomics index to take into account about posture and joint physical limits. Moreover an energy optimization criteria has been included in order to find muscular activation coefficients. The proposed model has been used to perform an inverse dynamics analysis of automotive steering operation in order to assess the muscular activity and the spatial attitude of each link.