Hello,
I think you are improving your sense of movement is nice, I can see how the sketch would move just from the few lines. That is something I am struggling with for example.
Just a tip make your drawings bigger so that there are maybe 2-3 on a page if they fit. This way when you get into the longer times, like 15-25 min, you can easily draw in the detail because you actually have the space to create it. Also mabye watch a few videos about anatomy on youtube once you get into it, Proko is a good channel. This part will probably be really frustrating because experienced artist know probably most muscles in a human body to improve their drawing skills.
I hope this helped.
