Poser musculature and skeletal structure is "painted on" and does not move under the skin the way it does on a real human.

No offense intended, but that's not a limitation of Poser, but of practically every app out there, XSI, Maya, or whatever. That's why people spend weeks and months studying topology in an attempt to improve their ability to make morf targets and blendshapes that better simulate the effect of real skin sliding over real sinew.

Lately, true soft tissue dynamics have started to become available to the very limited high-end market, but the use of those features is very sparse, mostly limited to firms like ILM or WETA that have the processing power to handle the massive calculations required for a simulation.

But to say that you need a high-end application to achieve something close, particularly in animation, where the use of 24 frames per second can mask details that might give away the nature of the application is limiting and closed-minded.

If you had said, however, that there is currently no Poser model available to do it, we'd be in agreement. DAZ may be good modelers in a sense, but they are simply not animators, as becomes apparent to anyone who has experienced broken joints, deformed anatomy, or unstable morfs while trying to make their figures animate. They are getting better, but there will always be limits on what a stock character can accomplish.

So the solution, of course, is to develop specific characters for the purpose at hand. For that, I can offer you some direction:

1. Get Wings 3D. (It's free)

2. Learn the toolset, which is very simple, by following a tutorial or two here at Renderosity.

3. When you understand what an edge loop is, and can recognize topology, read these threads while you work:

Facial and Experimental Topology Discussion

Stahlberg's Body Topology Thread*