I recently looked up muscle systems for Blender, and the latest post I could find was from 2009! What happened? The post was really good too, showing a guy punching http://www.blendernation.com/2009/05/08/blenrig-30-alpha-is-out-with-muscle-simulation/.
You’d think It’d be really easy. All you have to do is set up a system of mesh driven by shape keys from bones, and then make the skin and make it shrinkrap to it. At least that’s what I think, but I’m no coder, just an animator who wants realistic results withougt having to use Maya
There is a BlenRig 4.0 out now.
Might be it’s not as easy at it seems, and might also be, that there are not enough Blender users and coders interested in the matter (pity!).
Shrinkwrap tends to do things you don’t want, in joint areas, where influence areas of multiple shrinkwrap modifiers overlap, and at some other occasions. Furthermore, it requires fairly high subdiv levels to work well, making things big and slow.
Probably it would be better to have some other kind of deformer available to simulate muscles.
Aside of that, setting up a shrinkwrap-based muscle system isn’t a matter of coding. It’s just making use of the existing set of tools … modelling, rigging and skinning. None of the required techniques is particularly hard - it’s just the fine-tuning required to smooth out all the ugly artifacts, that will drive you mad … and I don’t see a way to automate that task.
So, if you feel your character needs a dynamic muscle system, you probably will have to go through the nasty details yourself, and build it manually (sorry to have no better news for you …).
BlenRig 4.0 seems to have no muscle system (yet?), has it?