Geneome takes a look at creating or faking a muscle simulations in Blender in this demonstration showing how it is possible to have an arm set up so that it appears that there are muscles at work expanding and contracting as the arm moves.
An advanced tutorial on creating and animating fake muscles in Blender using armatures, weight painting and shape keys
This is a pretty common setup among all 3D applications, that is if you are not choosing to go the dynamic muscle route for your animation and rigs. Here, Geneome shows how to create the look of muscles by using weight painting, and set driven keys, or Blender’s Shape Keys.