I would just say that when you ghost the rest of the body, spend a little more time with proportion or position. I'm looking at that 3rd one in particular. The focused forms look good though.

You seem to be struggling with drawing 3 dimensions more than anything, so I would suggest learning THE paramount drawing fundamental concept first before you go too hard into anatomy. Which is that… Drawing is fundamentally 3 dimensions on 2 dimensions therefore (after learning perspective): .Create simple forms that YOU understand .Literally turn your mind’s eye into a 3d program (I mean be able to draw what you want with your fingers in actual 3d space right in front of you BEFORE drawing it with a pencil) .Don’t worry about anatomy as a priority .Add the anatomy to the forms you develop (or outright change the form you develop to something that is closer to the anatomy when you’re ready to add complexity) .Draw loosely in a way that you can maintain your mind’s eye’s sight on YOUR form: and use the form in your mind’s eye to inform what you find to be aesthetically pleasing and not necessarily what is accurate P.S. the back is very complex (and is really only necessary for details and understanding movement/proportion)   You can typically get a very convincing back with highly simplified forms P.P.S. Sorry if this wasn’t about the anatomy of the back and shoulders but you seemed to have far more pressing matters