Great narrative poses you found there. Especially with short sketches there is always a spectrum between exact proportions and expressiveness, you situated these closer to expression, without losing too much proportions. I like the way you represent the different body types, it gives a very substantial, down to earth vibe.
As I understand you work on a graphical tablet. If your tablet is pressure sensitive, tweaking the software settings to allow a variation of line width with increased pressure might be an interesting artistic decision, to emphasize the dynamics of your lines even more.
Well, well well, Flandre16 (TheWood), I do say. Your sketches are magificent in terms of their speed. Greastest job!
However, I've got one tiniest, smallest, littlest and teeniest idea to help you improve: I love how quickly you sketch out your figure humans, but would you please kindly do us a favor, and do 30 minutes of 30 second animal sketches in this website, and many others? (60 creatures)
The reason is because, though it's completely, totally and positively outside the boundaries of your department, but it cannot hurt to just do it.
Good luck to you, and your next goal.