Say, these quick sketches, 30 second, are totally striking, starwave. That's very spontaneous. (Even the 1 minute poses)
I've got one idea of improvement: I love how much freedom of lines in your half-a-minute sketches, but if you're new here on this site, they have a little bit of rigidity in the perception of edges. Why don't you please loosen up your hands, with Crayola crayons, on notebook paper, with 35 minutes of 30 second drawings?? (2100 seconds/30 secs=70 quick sketches of bodies, all with your whole shoulder, instead of your wrist)
The reason is because, it can and shall aid you in making visual communications, with the bold strokes, done very lightly first, and to spend less time of the details.
For more vital details, be sure to look at this drawing tutorial from Youtube.
This has some related info that's applicable to anything and everything.
These are interesting to me -- they are very different than how I approach figure drawing! Your approach seems very systematic -- looking for precise shapes inside the figure. I know that's one approach that many people like, but it does end up looking more like mannequins than people. There's not the same sense of FLESH, you know? I'd be curious how you might progress if you set this approach aside for now and tried looking more at the outside shapes to see what patterns lie there. In the shorter gesture drawings, what would it be like if you never lifted your pencil? On the longer ones, how can you make the final drawings look more like they have flesh?
Those are just suggestions from a learner! But your sense of the relationship of the inner shapes is quite strong and I wonder how thinking about figure drawing differently could help you grow even more.
I really like your sense of shape and the fluidity of your line of action. There is a bit too much focus on getting the shapes right in the later sketches that make it seem a bit unbalanced and rigid. I think it's good to focus more on the flow of the figure as a whole first before worrying about getting everything else right. Overall I think this is a very good attempt!!
My idea for a next step would be to advance that sphere shape you use to represent the chest area towards a flattened egg shape, that is closer to the actual anatomy of the chest. You will have to reduce the distance between hip and chest quite a bit, to make that work.
In the short exercise you always use quite a lot of lines to represent a single sphere. If you manage to draw fewer lines with more control the result will be clearer. Maybe spend some warm-up time just on practicing circles free-hand.