Just look at any anatomy books . Anatomy for artists specifically, but anything is good! See if you can find the ones that show the actual muscle though, just as if the skin has been stripped from the body . Best way to see how the muscles shape and work together, which is going to be very important for a muscle man, since all of the muscles are going to be quite exaggerated and huge!
Here's a few that I found with a quick google image search
. Anatomy for artists specifically, but anything is good! See if you can find the ones that show the actual muscle though, just as if the skin has been stripped from the body 
Linear Mode
