I wonder how efficient it is to do an anatomy study out of a stylized image? Certainly better than no study, but I feel like a photo could give you more subtle muscle positions.
Anyway, to answer your question, do you usually paint in this style? I find that when i try to make a study of someone else's style, it takes much longer than my usual works, even if the style is seemingly much simpler.
As Malcom said, practice makes perfect :), I wouldn't beat myself up over one (or a couple) time-consuming images, as long as you learn something from them. For some people, even 10 hours on a piece like this can seem fast, depending on their skill.
