Yes, but would you really want to animate that?

Professional programs can actually have cloth and other stuff like muscles added to the character, and the program uses real-time physics calculations to move the cloth/muscles, and then adds it to the animation. This allows you to only animate the core skeleton, and the rest is handled by the program.
Infact, most professional games don't even use animation programs anymore, they have the developers put on a suite which records their movements, and that is then translated to the model to create an animation. I'd love to have access to this technology one day
Anyway, back to this flexing muscle... If you could pull it off to code such a shader/function/animating program etc. then yes, it would be an awesome product idea
TheComet