If you ask me, being able to draw or sculpt the human body in any pose you desire and do so realistically (which I'm not, BTW), is the pinnacle of artistic ability.
It's hard to do it without a reference; you can use a model, but that is not the best solution and, above all, you depend on other people's willingness and availability.
To overcome that problem, you can get yourself an articulated mannequin figure. You can move each articulation modeling virtually any position a body can adopt, place it in front of you, and start drawing or sculpting.
As many often as you want, until you are satisfied with the result. Grab yours now, picking among the three sizes available.
We have to prepare each shipment individually as they are ordered, so allow us in 3-4 weeks for it to arrive in USA/Canada (to be safe) and 3-6 weeks rest of the world, though thy are usually delivered much faster.