You show a beautiful understanding of the refrence and melding it into a personaized sketch, the fluidity of the poses makes everything flow SO GODDAMN SMOOTH!
there aint nothing id change about these sketches cant wait to see more!
Oh, I love that foreshortening you did on the bottom left figure's legs, that seems to be on point! Good job!
As far as I can see, you are pretty close to understanding the form as a 3D body. (I try to explain myself through a language barrier, bear with me.) For example, the left calf of the bottom left pose has a mass, it sits on a plane, etc.
But on another places the muscles are not in their places (top right arms and left thigh). It will inevitably work itself out if you keep on doing studies, no need to worry about that. But also I would recommend hitting up an anatomy book, see where and how connects to what (feel free to copy the pictures), then what I would do in your place is find some references of the problem areas and take a long winded, calm study of the picture. Try to see the thing question in your minds eye as this 3D model you can spin around, that helps a LOT (Bobby Chiu of Schoolism on Youtube can explain this visualization process to you better than I could).
Other than that, honestly, you are on a very good path. It's a bit wobbly in places, there's some nervousness and stiffness to the poses, but nothing unsolvable. Good job! Keep on drawing!