One of the most important aspects of sculpting is anatomy and I am always studying it. Anatomy is not something you ever can completely learn. There are no books or courses you can read or take and viola! you've learnt anatomy! (Don't get me wrong school is always a better option than self teaching, but everyone continues to learn after school as well).My philosophy is that anatomy is a continuing study, that as an artist, I strive to keep learning.
One of the best series of books for anatomy is Burne Hogarths's series of books on anatomy. I have all of these in my reference library and they are invaluable. Part of the reason for this is the way in which the drawings are illustrated. Most of the muscle groups are broken down into thier base shapes, which lends itself to sculpting because the shapes are the same that you would form the putty to sculpt them. His drawings give clear definitions of the muscle groups without being confusing like other more technical medical anatomy reference.
Copyright ©2003, By Burne Hogarth Dynamic Worlwide Media LLC.
Throughout this post there are a few samples from his book Dynamic Figure Drawing. Each muscle group is first shown as a shape which helps you visualize the individual muscle. The drawings are clear and easy to read and naturally relate to sculpting.
What I like about these books is how clear they are. When I first started sculpting I was using medical anatomy drawings and while they were very precise, I found them very confusing and difficult to interpret. I was lost until another sculptor Jeff Grace showed me these books, and I am grateful.
So if you are having problems with anatomy here is a good place to start.