My understanding is that each pass (muscles, tissue, skin) has its own external collision settings. I was wondering how I would accomplish an external collision object to affect the whole simulation starting from the skin.

For example, if a rope is tightened on the thigh of an `injured soldier` character, would it be possible to affect all three passes by the rope? Since each pass feeds into the next one, I'm a little confused about the integration of external forces. Since in real life collision starts from the skin, and then affects the deeper tissue depending on the force.

Another way of phrasing my question is:
In a muscle/tissue simulation, is it possible to use external collision starting from the outermost layer 'skin' of the character, and affect deeper layers all at once?

It's possible to re-enable softbody dynamics on the cached muscle and bone geometry being supplied to the TissueSolver.
By toggling TissueSolver > Advanced > Relax Internal Geometry you enable a pin constraint that attaches the muscle and bone geometry to the incoming animated positions. If a pin stiffness attribute exists on the cached geometry, it can modulate the pin attachment strength. With a weakened attachment strength, collisions and other forces will push the cached geometry away from its animation.

In the flipbook below, the external collision object is pushing on the tissue surface. By painting a pinstiffness attribute on the cached muscle geometry, the collider is able to affect the otherwise rigid cache as a softbody. On the right, you can see the displaced muscles extracted from the sim.

Hi John,
is it possible to share the setup as a hip file?
I got the Muscle_and_Tissue_Workflow_H19.0.568_v03 running.
Seeing the setup would help me a lot.

Cheers Christian