I have no trouble at all finding photos to use as a base, albeit it's much harder to find men than women. And yeah, photos. Because I don't have the life-drawing classes oppurtunity yet.
I have relaxed and sexy poses in bulk. I'm looking for strenuous poses. Showing real muscular action. Outstretched limbs and whatnot. Martial arts stuff would be ideal.
Now I'm sure, somewhere on this internet, there's a treasure trove for these pictures, or a close substitute. But hackneyed attempts at Google aren't going to uncover them for me.