The 3D deformation of a muscular aesthetic unit has to be superposed with the deformation of visco elastic elastomers in anisotrope spaces.
To perform such 3D reshaping without volume or mass increasing, you need to work thinking always 3D using
vectors and tensors.
Vectors are normal to the muscle layer.
Tensors are following sense and direction of the muscular area
The angle between a vector and a tensor has to be usually 90 grades.