The shoulder is a complex joint with many muscles acting between the scapula and the humerus. Thus it is obvious that the mechanical system is indeterminate and an optimization method has to be used to find the muscular forces acting on the glenohumeral joint. In the LBO, an optimization method based on null space optimization had been developed (Aeberhard et al., 2009) and applied to a numerical musculoskeletal model of the glenohumeral joint (Terrier et al., 2007). The goal of the project is to use this optimization approach to determine the forces of the muscles acting on the glenohumeral joint during a simple abduction motion and activities of daily living.