Creating 'floppy skin' for muscles, and bat/dragon wings:

This technique takes advantage of the integration of Maya's tools, this enables us to combine skinning with softbodies, and thus create the effect of muscles or skin moving due to inertia.

You can download a final example of a dragon wingbeat here

The basic idea is simple:
-first you bind your geometry to your skeleton (or whatever, this works equally well with blendshapes).
-then you select the surface that should have 'floppy-skin'
-and create softbody.

!!Make sure!!! that you use 'Duplicate,Make Copy soft' and 'Make  Non-soft a Goal', this will let the softbodies follow the bound skin with respect to the goalweight of each CV/Particle.

-then select the created softbody-surfaces and go into component mode, select the CV/particles and set their goalweight using the component editor.
Alternatively you can use the Paint Attributes tool to paint the GoalPP values.
1 makes it stick to the original surface
0 makes it totally disregard it
everything inbetween makes 'floppy-skin'.