Muscles in a Shoulder Model: Identification of the necessary number of muscle cables

The shoulder complex is a complex articulation of the human body. It consists of several bones and joints and is moved and stabilized by 16 muscles. The muscle forces can not be measured experimentally, but can be computed using numerical methods. An existing numerical model of the shoulder uses inverse dynamics and nullspace optimization to compute these forces. The muscle segments in the model are modelled as cables that wrap around the underlying bony structure. The project’s aim is to adapt the existing model and introduce the parametrization of the number of cables. Therefore, origin and insertion areas were interpolated with curves and the muscle cables were evenly distributed on these curves. The results showed that at least three cables per muscle segment needs to be used, to get consistent results. The present work demonstrates thus, that the number of cables per muscle segment plays an important role. The necessary number of cables should always be investigated whenever muscles are simplified by cables.