That does work! Your sketches have incredible texture and flow and feel very weighted. I would recommend trying some exercises with figures other then the human body because you seem to have it down very well.
Your sketches have a lot of really good motion and general shapes down, but none of the sketches seem to have any particular detail aside from the one of the hand, so I would say doing some longer timed periods to get more detail in would be beneficial.
You don't sketch like a beginner! My advice would be to limit yourself to fewer lines, resist the urge to use scribbly, fussy lines. You have a natural feel for action and form,give yourself exercises to under 20 lines for instance when you're in a 5 minute or longer pose. If you haven't done so you should practice the facial expressions too, you have what looks like a knack for caricature, and that would be fun to explore!
Your work is really good for a beginner. I like to use a skeletal fuction to help support where the each aspect of the body goes and the head. Like circles and lines to map it out and then later filling it is. Other than that your work is pretty good. Keep it up!
Wow. Those definately don't look like beginner sketches. I would agree with one of your other critiques to maybe try using fewer lines, or possibly just picking one aspect of the reference to focus on rather than the whole, such as a more detailed drawing of parts of the anatomy, like an arm, or a head.
Also some value studies (shading). The best advice I can give is to keep track of landmarks, or where things are in relation to other parts of the drawing. When drawing from reference its easy to not see the forest for the trees and then you have instances like with your hand sketch where one side of the palm looks too high for the other side even though it is drawn relatively well.