I'm looking for animations of muscle-flexing or bodybuilding. There are bodybuilding poses in DAZ, but of course, no animations. This seems so obvious I'm genuinely surprised how it's not available.

For muscles getting bigger, you need to make a morphing sequence. See this tutorial.

Thanks a lot, and that'll come in handy later, but I was looking more for muscle-flexing animations -- you know, pumping into a double-bicep pose, showing off the quads, that sort of thing. But yeah, I know this morphing sequence will make me real popular at DeviantArt.