Oh wow, I must say that I'm extremely impressed with your human anatomy, especially since it's one of the first I've seen from you. However, I do have some suggestions.
In the top left picture you did very well, but the man was a little thin when in proportion with his pecs. To be honest I think that the right line covering the outer shape of the stomach causes more problems than the left. It's in the excellent shape and expresses the muscles well, but it just curves in a bit too much. Again, maybe it's just me being nitpicky. Also in this one there is the raised harm with the hand crunched in the fist. I won't talk about hands since it's a common subject that almost every artist struggles with. But I do intend on talking about the muscle on the arm. It's a little big and exaggerated. Again, just take away the curve of both sides a little bit, and it should be fine.
The top right one has excellent points. I think you did very well on the head and neck. However, with the torso and arms I have some suggestions. The torso in men is very tough, since the slightest exaggeration can make them appear to have curves, which men generally don't have. I run into this constantly, which is why you don't see many men coming out of my gallery. XD
But again, the lines on a man is he is more muscular are easier to express if they are more sharpened and less exaggerated. Something that helped me and that I see you're already beginning is that I always begin the structure of a man with boxes. It just makes it easier to receive the curveless results when you start without curves.
The others have similar problems, and there's no real need to repeat myself. You've done really well so far, and I'm surprised at your steadfast improvement. Well done my good sir, I shall tip my hat to you on the way out.