https://www.thegnomonworkshop.com/tutorials/anatomy-for-artists-understanding-the-back-and-shoulder-muscles-with-rey-bustos

“Artistic Anatomy” refers to the essential muscles that create the visible shapes that we see on a model’s physique. Rey Bustos, famed illustrator and anatomist, teaches how to illustrate the complex back and shoulder muscles in a way that is preferred by most artistic anatomists.  When illustrating, it’s not necessary for artists to know every single muscle of the body. By editing the key number of muscles that artists need to know down to a minimum, Rey begins the workshop with a focus on the Sacrospinalis (or Erector) spinae group — some of the deep muscles in the center of the back that can be found along the spine all the way up to the base of the skull. These complicated, often-stringy muscles are important and keep humans upright — but they can be challenging for artists to study individually. Rey reveals the simplest way to understand and interpret this muscle group and teaches easy-to-remember strategies for illustrating the forms.