Drawing the anterior fibers of vastus lateralis.
Watching someone draw on a body or drawing on the body yourself is a great way to study anatomy. By visually locating boney landmarks and drawing the muscles that connect them we can improve our understanding of surface anatomy.
Palpating the tendon of latissimus dorsi helps me organize fiber direction while drawing.
When we trace layers of muscle (I'd recommend working from deep to superficial) we can appreciate variations in muscle fiber direction and lines of pull, synergistic and antagonist relationships, and of course the organization and relationships of the layers, themselves.
When the model adds movement, outlines of bone and muscle don't shift as dramatically as the structures underneath the skin. But there's enough movement to visualize what is happening to the body in motion.
It seems like every time I have some extra cash I buy another skeletal model...
(If you draw on a model wearing a unitard, extreme movements and stretches are easier to see because the fabric stretches more than skin.)
Click on the link for my post about our (R. Sikoryak, and my) upcoming Anatomy For Cartoonists class in September.