Due to the steady increase in the ageing population, the number of people with joint diseases is growing and therefore the topic of joint replacement is becoming more important. In order to design a replacement extensive knowledge about the joints contact forces is required. The difficulty is that these forces cannot be measured directly; consequently we need to rely on modelling. Biomechanical models of the upper limb are capable of predicting internal forces, and can be used for understanding the shoulder pathologies and ultimately as a tool to assist the surgeon.