I learned how to draw figures in high school partly assisted by following a series of books on the human form by Burne Hogarth. The system he used was more detailed than systems I'd read about in other books, which were focusing more on abstracted forms rather than how those forms connected and transformed through movement and viewpoint. Hogarth showed quite easily how limbs and muscles were connected to each other and what proportions remained consistent while others transformed by movement and perspective. I found I was better able to draw figures in action and foreshortened by following his work. Unfortunately it seemed to backfire for me in college as I tended to idealize the human form after Hogarth's style and I was regularly criticized by professors examining my work who I guess too easily recognized where I was borrowing my style.
By the time I was drawing the above image I didn't really care what anyone thought of my work. Several thoughts were going through my mind in creating this. I was attempting to show someone eating a sandwich, thus the right arm position, but I wasn't drawing from life, so it didn't really come out as I hoped. Later in talking the drawing over with someone I mentioned how the proportions of monkeys and apes are different than humans, thus the quick sketch of a monkey swinging from a perch.
Sometimes mistakes lead to lucky insights, but this wasn't one of them. The figure's torso is leaning back and while appearing somewhat relaxed, the left leg doesn't seem to be angled properly for the rest of the body. Not surprisingly I've not really done anything else with this sketch.