The Muscle Creator window lets you use naming conventions to mirror muscles after they have been sculpted. The muscle for each “side” needs to be parented to joints/nodes that follow a Left or Right naming convention (or something similar, like Front, Back), and each muscle must have been created with that naming style. For example, if your naming convention is to differentiate between left and right using _L and _R, the first muscle you create should be named something like Bicep_L or Bicep_R.

To mirror a muscle

1. Select Muscle > Muscles/Bones > Muscle Creator from the main menu bar.
2. Click the Create tab and find the Mirror section.
3. Select the axis you want to mirror across.
4. Enter the naming conventions you want to Search/Replace for. ( -click the field to bring up some common cases).
5. Click Mirror Muscle from Selection.