MuscleBasic Coord. Object Dynamics Falloff
A new muscle system has been implemented in R13. As with the old muscles system (from Cinema 4D R11), it is based on actual muscle objects that you can shape based on their length and then add a Deformer
Muscles can slide under the mesh and push it, as before, but can also pull it to take into account loss of volume (particularly useful when the muscle is stretched). Additionally, muscles can now have dynamics applied to them (no collisions, though), so they can react to gravity, motion and emulate their mass better.
These muscle objects can be anchored to other objects, joints or whatever you want so they can be stretched and squeezed the way you need them to.
Adding muscles to your character is fairly straightforward:
That's it. From there, you can start creating your different muscle shapes for each state (or let the Muscle object calculate the volumes automatically) and adjust various settings if you want more control or dynamic behavior.
The Muscle objects themselves can be rendered, so make sure you hide them if you don't need to see them in your final render.
This is a great way to refine the way your muscles affect your mesh.
Keep in mind that muscle objects need their own Weight tag, and not be mixed with joints or other objects, otherwise their influence will be normalized, instead of added on top of existing weights.