Nice! I like how clear and structured everything is.
A couple of things I'd be careful of is balance and the waist. It seems like the legs are pushed a little too far to the left. It might help to get a ruler and line it up with the middle of the chest and look at where the legs line up.
You have a good width for the ribcage but the waist/abs are really narrow. I think it's up to the artists to change up proportions when we draw, but since it's a study of the muscles it might be worth making the waist a little wider.
Overall looking good, hope this helps!