These are beautiful. So effective while very simplistic at the same time. I immediately recognized those profiles. My only critique would be the hair on the 1st portrait is blue and black which I do enjoy but I think if you added a little more green into the blue then the cool olive colored skin tone would mesh better.
I think you did a great job and specifically the legs on the left most figure and arms on the right most figure show the realistic muscles of human anatomy. I think you could up those curves even more. It may be helpful to look for references with very muscular people to learn about how the muscles interact. I find that those curves and slopes are what provide more energy behind a pose. Great job for your very first lesson!
