(The image from the blog post is a Michelangelo anatomy study)

"The more you know the better you will paint," Leonardo Da Vinci

This is one of my favorite quotes by Da Vinci, and it is right on.  You need to know your human anatomy inside and out. Complicated movements of the shoulder girdle, the knee joint, and etc, are not just bumps, your anatomy controls these forms. 

You will first need to understand your basic 2D anatomy diagrams, then have a complete 3D understanding, and finally understand the movements of the body (kinesiology) and how the superficial forms change. 

Outside of finding a great artistic anatomy instructor; these are your to go instructors, Stephen Perkins,  Michael Grimaldi, Dan Thompson, Jon DeMartin, and Frank Porcu, the books listed will help immensely.

Investment time, you will need to purchase a few anatomy books.  Some are expensive and some are cheap, but they are an absolute need and you will use them all the time, using them to the point where they are so worn out from constant use you will need to purchase a second copy. I'm on my second copy of Die Gestalt Des Menschen and third copy of Artistic Anatomy. 

1. Die Gestalt Des Menschen by Gottfried Bammes (its in German but the plates are incredible)

2. The Dictionary of Human Form by Ted Seth Jacobs (the only book with rhythms discussed)

3. Artistic Anatomy by Dr. Paul Richer (great proportion plates, and origin and insertion descriptions)

4. Complete Guide to Drawing from Life by George Bridgman

5. The Human Figure by John H. Vanderpoel

I suggest you read them all and then copy all of the plates cover to at least twice.

I copied all of the books listed above 3 times, cover to cover.  I would do it mostly in the summer between semesters to keep the momentum from school studies in spring rolling into the fall. 

Extra credit, you can purchase actually dissection tapes - Acland's video atlas of human anatomy by Robert D. Acland.