Using GhReactions results in lower joint reaction force


using the quadratic solver in my modified standard (van der Helm) shoulder model and the initial arm pose (abduction/flexion = 0) I get a lower reaction force when using the ghreactions. On the contrary the angle of the impacting force (angle in the scapula coordinate system in the xz-plain) rises.
When I shift the humeral head the difference between the outcome varies even more.

So what is the reason for lowering the reaction force in the gh joint when using the ghreactions?


I am a little unsure on the two situations you are comparing so i assume that it is a comparison using the ghreations file and the normal reactions present in a spherical gh joint right?

Using the GHReaction.any file will constrain the reaction force to be within the glenoid, the resultant force can not point outside the edge of the glenoid. The GHReactions has been constructed using multiple pushing muscles which are strong, these muscles points from the glenoid edge to the gh rotation center. These muscles are recruited like normal muscles. This setup ensures that the resultant force can not fall outside the edge. In this way it will also change the impact angle by restricting it compared to a normal spherical joint which has total freedom.

I hope this made it clearer otherwise please ask again.

Best regards