I have watched a good number of YouTube videos on drawing mannequin representations of the human figure, including gestural diagrams. Of them all, one set of videos focused on the basic mannequin in front, back, side, and three quarter view. I find these to be the platform necessary for drawing mannequins in motion. Below are the four basic poses considered. The 3/4 view tends to be the view that gives people the most trouble. Notice how the shoulders in the 3/4 view are halfway between their positions in the side view and front/back views. As the rib cage, hips, and face turn in the 3/4 view, the width of the far side gets smaller and smaller. There is still a straight line from the far shoulder through the neck to the near shoulder, but the far shoulder is a touch higher than the near for perspective.
I show this diagram here, rather than just listing the urls of the tutorials because the videos are sometimes maddeningly slow. So, if you get to the point where you are pulling your hair out, I wanted to show you the end game so that you can practice them on your own. Although the videos are longish and slow, if you sketch along with the videos, they will actually turn out to be at a good pace. I couldn’t find the first video, so I actually start off with the second. But there isn’t much to catch up with.
Let me know how the videos work for you, and enjoy.