More important than just doing drawing off masters drawings is to try to understand why they were drawn that way. What did the masters know about the suject material and why did they draw them the way they did. The form of the body, the way the light hits and moves acoss, the battle between the light and the shadow over the surface and whatnot. You seem to be grapsing some of the important concepts, you have established nice form in a few of the drawing, and I dig the fact that your stroke is following the body instead of just outlining and coloring it in. Keep up the good work and think about what it is that you are doing, and what they must have gone through to make what they did.
hey man, I think you should work on some gestures a bit more. Copying off the masters wont help you out much at this point.. maybe it will even confuse you. Work on 3d volumes, because your images look kinda flat, at least the first 3 images. Shading isnt enough to say the image has volume. I dont know how David Hockney's original drawing looks like, but those proportions are wrong. Stick to gestures man and work your way up. I swear it will help you alot.
And by the way, Burne Hogarth IS a master. like it or not. a modern day one at that
For 3d stuff, I suggest you begin with simple objects like boxes and cones, and spheres and cylinders. Most of these objects when put together in a certain order will help you define how the volumes in the human body look. In fact most of the complex shapes you can see everywhere are just a sum of a bunch of the basic figures. So go and draw them the most you can! Remember... shading doesnt necesarily help you define if something is 3d or not. So try to make an object look 3d without shadows. It sounds hard but once you get it will help you alot.