good work man, keep at it and draw as much as possible. you seem to be observing stuff well in the last update, there is a good sense of depth and dimension to all the objects. keep doing these, but also do some posemanicas perhaps???
if your not comfortable with doing them this fast, there is a section on the site somewhere where you can just bring still images up and stuff. i think don't worry about specific muscles yet, you want to learn the overall form of the body and perhaps get comfortable with posing and foreshortening....? THEN you can focus on more in depth anatomy study.
like always, just suggestions, i'm no teacher
DRAW DRAW DRAW!