As an art student myself, I would suggest the following ideas. Since these are called gesture, where the student is trying to get the general idea of the human body and how it changes when it is "in motion", the ideas of martial arts/yoga/exercises are good, but also think about ways that you can move (and hold a pose) that would show someone possibly just starting out in art the many ways that we think a body moves, but doesn't really. For example, what does the body do when you are bent touching your toes? How does it balance? How can you shift yourself into a way that looks like you shouldn't be able to balance and yet you can. These poses are the best mainly because when people think of the human body, they do not realize that the torso moves to a place where something is under it and supporting it's weight (as long as it is not laying down.
) Thus the reason that yoga or fighting poses help us see that. But also use poses such as "the stretching for the very last glass in the really high cupboard without a chair because you're sure you can reach it" type poses of everyday life. Those poses are what we as artists want more of.
t Redjake: yes, that is a bit of an immature idea. Most of the models might have a nice or ok body, but remember two things about these classes: First, the woman or man is not an object of sex, they are a tool to help the artist see one thing and that is how an actual human body moves and twists and how our preconceived notions can ruin our art. The other thing is that while some may have a nice whatever, there are more often than not older women, larger men, etc; these classes are to show an artist that not all humans look alike, not to get them hot and horny.