The book I suggested focuses a lot on anatomy and people in perspective, I believe. Loomis also has a figure drawing book, which goes into more detail.
No resource will teach you to understand human (and non-human) bodies though. Everyone thinks about things in a different way, so you need to create your own mental conception of things, based on the things that are important to you, the patterns that you notice.
Drawing books are a good place to start to get a grip on things like ideal proportions and the basic shapes that make up human bodies, but you'll want to branch out if you want to be flexible as an artist. Look at real people (and animals, etc). Watch how they move, how far they can bend and stretch. What features do all of them have? What tends to be most pronounced? What tends to vary the most? How do the various parts deviate from the basic forms? For example, arms aren't quite tubes, they're somewhat conical, flattened and twisted.
Do life drawing if you can, work from videos and photos if you can't. Don't worry about copying references to look pretty and just like the photo, instead focus on the structure, on conveying the 3D form in 2D. Do quick gesture drawings and quick sketches, don't bother rendering details.