If you cant get your hand on mocap :) you have to animate it in hand. One way would be to start by adding all the key frames, and then fine tune the in-betweens to fit your needs, and for the muscles you could make a morph to control the vibrating, and maybe add a noise filter/controller of some sort, if thats possible in poser(not sure if it is).

Anyway doesnt do a lot of animation so might not be the best way, but guess its one way to do it :D