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. 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 innovative aid to drawing, sculpting, and learning surface anatomy. More than one hundred static and active poses are included in Visualizing Muscles. Paired photographs — one painted and labelled, one not — show how the simulated muscles produce the subtle lights and darks, hills and valleys, on the model's unpainted skin. Captions highlight the muscles called into play by a given pose.