# How to model muscle contraction force acting on two bones connected by joint in Unity/PhysX?

I'm trying to understand what is a correct way to model a muscle contraction in a physics engine like PhysX (Unity3D). Muscle that I'm modelling is connected to a bones in 2 points A and B.

Having a total force for the muscle fTotal, I'm trying to apply two forces in points A and B on corresponding bones, where magnitude of each force is a half of the total force. And of course force vectors are lying on the same AB line and pointing to the opposite directions towards the center of the muscle.

fTotal = ||fA|| + ||fB||


One thing that bothers me is a situation when one bone is fixed in space. Intuitively, all contraction force should be applied only to a single attachment point, however, my model will apply only 1/2 of a force. Can you suggest a better way to implement this?