I have an idea how to make an simple simulation of muscles, i´ve tried it in Si-XSI and 3dsmax, and it works quite fine. It can be done, when :1)the starting and ending bone(root-effector) can be linked to various bones in tha armature(e.g.arm-ellbow) without braking the chain. 2)the length of the muscle bones would have to be linked to the distance of the start-end points/bones of the chain, (scale z = distance start-end*some constant)3:the x,y of the muscle bones would be linked to the distance, but in another way, for the bulging(scale x,z = some other constant/dist s-e).
if anybody interested in this, i can post pictures, but later. I am not a coder, but i think it could be done with some kind of constraint. it would be then a special kind of armature structure, which is not animated, because it animates itself in dependence of tha main armature rig.
I actually have done a patch that does exactly this; unfortunatly, I could not figure out how to adequatly control the roll rotation of the bone- I could either make it face "z-up" or another axis up. Been busy with other projects recently, but I think what is needed to change heading but not roll of the bone, so if the parents twist the children twist with them. You could then do the muscle with two bones and some vertex-paint.
I'm going to get back to this (got another milestone to reach first) and I'll post the patch. Stay tuned.