Sorry, didn't know that. I cannot edit my reply so here it is translated:
Your sketches are pretty good, but in many poses it seems that the bodies do not lean properly, it feels as if they were floating. I think this may be because you use many curved lines to define the figure. For example, in the 30 minute drawing the joints look very rounded and maybe that's what takes away some "strength". You could use more straight lines in the parts of the body where there is tension, and if you have many doubts see an anatomy book about the joints and muscles. It can also be a problem of the gesture on which you build the figure, but I think that whatever the inconvenience would help you take more into account where the weight of the body is downloaded in each pose :)
I would also advise you to check the proportions a little (in general you are fine, but in some drawings you notice smaller or longer parts that are not coherent with the deformation of the figure).
Regarding the feet, I recommend paying more attention to the form than to the details (and this is good to apply to anything you draw). You could take more time to draw them trying to discover relationships, for example: how many times does the thumb enter the length of the foot, how much does the heel protrude in profile, how big is the foot with respect to the leg, or how many feet enter a leg, etc. . Maybe you discover some interesting relationship and when you remember it when you draw it will be easier to solve the image you are studying :)
Well, for now I can not think of any advice to give you, so I hope I have been helpful and that you really speak Spanish (xD). Anyway, if I was wrong, I will write the comment in English later.
Regards! :)
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