Hmm.  Need a better way to simulate volumetric mass.  Something under the skin. 

Ideally a hard skeleton with softer muscle/fat tissue that the outerskin is being influenced by. Then you could also simulate muscle bending.

Without needing a bunch of joint controlled morphs that cant account for collisions and getting pressed on by external geometry.

 

Doesn't look like it would be easy to recreate something like this for example: https://www.youtube.com/watch?v=qXBnRehSCYI