If you're trying to construct the figure, try to focus on Gesture first then try to do the shorthand shapes (or Basic primitive shapes). don't get caught on Aesthetics yet..

Hi Imaginear. Try to keep your sketches simpler and cleaner and draw following precise steps, you'll see that you'll immediately encounter less difficulties. You did well to post the references, now let's see how you should proceed when drawing. Take a good look at your photos and try to identify the lines that run through them, not the contours. If you look at the line of the back and follow it downwards, you'll see that it virtually continues down the leg, all the way to the foot, a nice flowing S. Draw this line to begin with. Now look at the pelvis, just above the buttocks you can imagine a line going from one vertex of the pelvis to the other, sloping upwards.  Mark this line and use it to build a perspective box that will be a schematic pelvis. Connect the leg that is not included in the main movement to this box. What you should now have is a kind of very schematic skeleton, which you can use to construct very simple shapes for the legs, the pelvis (which you already have more or less) and the ribcage. Once you have these shapes you can start drawing the muscles. Only after that can you start applying some shadows, but don't worry about that for now. For now concentrate on the gesture and don't worry too much about the rest. Learn this step, slowly, until you feel you have understood it and can easily spot it by looking at a reference, after which you will be ready to move on to the next lesson. And keep it simple! There's no rush, it doesn't matter if you do it in a day, a week or a year, it's not a competition, you're here to learn :)