As the human body moves, muscles contract and relax, creating subtle changes in body contours and shifting patterns of light and shadow on the skin's surface. Visualizing exactly what happens beneath the skin to cause these changes on the surface is an essential skill for artists, physicians, physical therapists, and body builders-for anyone who needs to understand the body in motion.

But how do you teach this skill?

Why not paint a live model to look as though his skin had been stripped off and then photograph him in multiple poses? From that idea comes Visualizing Muscles, an...