>>277536108
As I understand, a technique used in professional CG where a bone's rotation doesn't just have vertex weights but also blendshape weights or something like that, so you could say make the bicep grow larger when the forearm is bent, simulating the look of muscles contracting. I'm guessing how they do it is essentially first creating the rig like normal, then bending it in all kinds of ways, and then manually correcting the mesh and saving that as a blendshape. Then they just use some kind of code to let the rotation of the bone change the blendshape.