You can make any NURBS surface connectable to the Muscle deformer by converting it to have a Muscle Object shape node. You can deform the NURBS surface however you want. Typically, this is done with one of Maya Muscle's proprietary deformers, however you can also deform it with any other Maya tools. This approach lets you convert existing NURBS-based muscle models, or lets you deform the muscle with your own tools.

To convert a NURBS surface to a Muscle compatible surface

1. Select the NURBS surface you want to convert.
2. Select Muscle > Muscles/Bones > Convert Surface to Muscle/Bone from the main menu bar.

   The objects are converted to have a Muscle Object shape. This shape provides basic settings to define how the muscle interacts with the skin deformer, as well as basic drawing options.

   Like capsules and bones, you can access the Muscle Object settings in the Channel Box, Attribute Editor, or from the Muscle Builder window Muscle Parameters tab.