Here's a sloppy paintover that helps, colored muscle groups as guides.
Look for these guys: Michael Hampton, (bought
this book a number of years back, what I've read is totally worth it), Ron Lemen, Rey Bustos, Scott Eaton. (Even just an image search w/ terms like anatomy/book/course etc. and you'll run into solid stuff, but definitely try out those books if you can.) I would recommend to study in roughly that order, because what they emphasize leads to sort of a learning curve, but a lot of their courses are self-contained and artists of any skill level can learn from that.
Googling medical diagrams helps also. But only to a point, because you're not gonna get a lot out of a drawing that provides only the details of complex forms, but lacks the ability to break those complex forms down into something understandable and build that up again.
In addition notice how parts relate to the whole. Gesture, 3d form is lacking in these drawings for example, hit the books on that! Also study how muscles relate to bone structure, how skin and fat lies on top of muscles.
Focus yes, but don't study only one thing in isolation, because it is ALL connected.
Keep it up dude.
