View Muscle Object
A Muscle Object is a special deformer in Cinema 4D that can create realistic anatomical effects such as skin sliding and bulging, stretching, etc. Characters that use this deformer can have an incredible sense of realism and mass, whereas lack a sense of life without it (although you can effectively mimic aspects with morphing, but its much more work to do so).
In order to see the actual deformation occur, you need to use the mSkin tag, which will map in the effect of the muscle displacement onto the rest of the skinning effect on the character.