ANATOMY ZONE

[Chris2Balls [:B]]

I would suggest you work on paper. When I mean paper, I mean... A3 minimum. You need loads of room to "free" your strokes.
Learning how to draw without looking at what you're drawing will help when you are doing this type of work.
If you cannot find real life models or do not fancy using yourself as a reference, go look for videos; I once spent an afternoon on one Bruce Lee video, stopping at moments which I found interesting so I could draw his body and in particular his muscles. I recommend videos of athletes too (slow-motion), like gymnastics, rowing, running... Knowing where muscles are and how they change in shape according to their position will give credibility to your figure.
But as Des and Zeemort pointed out, before you do muscles you need to get the general shape right- think of it like sculpting, where you carve out a shape progressively.
This being said, you seem to understand anatomy to a certain extent, you just need to keep working on it!