A quick muscle tutorial requested by
This is a reference to how the muscles are presented below the skin. You need to keep this in mind in order to get muscles proportionate to the body. Never draw muscles without a muscle anatomy reference unless you're 100% confident with drawing muscles
This is how you should outline the muscles. Try not to overdo the lineart for muscles. It can make it look over the top and blobby rather than toned.
On the left is an example of muscles in a final product.Yes, I know I messed up the crotch muscles of the example picture on the left >.<