In this paper, a multibody dynamics model of the shoulder-upper arm complex is presented. Three major bones clavicle, scapula, and humerus in the shoulder-upper arm complex are represented by rigid bodies. The soft tissues such as tendons, ligaments, and muscles are modeled as springs and dampers respectively attached to the rigid bodies. The joints between the bones are expressed as ideal kinematic joints. Kane’s equations are then used to derive equations of motion of this multibody system.
Based on the model, a person’s stand-up motion, aided by shoulder-upper arm complex force for lifting his/her upper body weight is analyzed. Commercial computer software is used to create the multibody shoulder-upper arm complex computational model and then carry out simulation. The model may be utilized in motion analysis of elderly people and sports medicine to study fatigue mechanism and prevent injuries of the shoulder-upper arm complex.