Hi zizka, I would really recommend that you go bigger with your current study. I feel like when you're learning fundamentals like anatomy, especially when using pixelart as your medium, you ought to go bigger. Right now I feel like when you're working at such a small scale, it becomes more about managing which pixel will symbolize a certain body part, and removes putting form into practice.
I think a good example of this is Ashcrimson, he has a massive thread on pj about his anatomy/sprite studies, but I feel like for the time he has been working on it not much has changed as I would have hoped (no hate to him ofc).
Even just upscaling by a little bit would make it less about managing each pixel- it makes it more about learning anatomy instead of learning how to pixel tiny sprites. If you do enjoy working at the size you currently are then keep on going!

quick edit to demonstrate.