Here is a preview of the new Cinema4D R13 muscles in action.
Muscles can slide, push and pull the mesh, and have dynamics (except collisions).
Their influence can also be restricted by painting weights on an extra weight tag, which is very handy and a lot more flexible than vertex painting. The extra weight tags allows to paint weight without affecting existing joint weights.
Note that all animation is done using Cmotion. No keyframes in this scene!