Any NURBS shape with a Muscle Object node can be used to skin with the Muscle skin deformer. Typically, you use the Muscle Creator or Muscle Builder windows to create and set up muscles, but you can also manually deform your muscle with any regular Maya tool. In addition, you can set up any of Maya Muscle's proprietary deformers on any object.

For example, even if you are not going to use muscles, you can apply a Muscle Spline deformer onto any object, even a polygon mesh, to deform it with a spline or Jiggle. You can also use the spline deformers to create a rig of joints along a curve for things like spines or antennae.