Simulation Study of the Upper-Limb Isometric Wrench Feasible Set With Glenohumeral Joint Constraints.

The aim of this work is to improve musculoskeletal-based models of the upper-limb wrench feasible set (WFS), i.e., the set of achievable maximal wrenches at the hand for applications in collaborative robotics and computer aided ergonomics. In particular, a recent method performing wrench capacity evaluation called the iterative convex hull method (ICHM) is upgraded in order to integrate nondislocation and compression limitation constraints at the glenohumeral (GH) joint not taken into account in the available models. Their effects on the amplitude of the force capacities at the hand, glenohumeral joint reaction forces and upper-limb muscles coordination in comparison to the original iterative convex hull method are investigated in silico. The results highlight the glenohumeral potential dislocation for the majority of elements of the wrench feasible set with the original iterative convex hull method and the fact that the modifications satisfy correctly stability constraints at the glenohumeral joint. Also, the induced muscles coordination pattern favors the action of stabilizing muscles, in particular the rotator-cuff muscles, and lowers that of known potential destabilizing ones according to the literature.