Very inspirational!

I would say that you definitely don't need any criticism here, on the contrary, your studies are very useful to allow others to understand the anatomy of these muscles (as well as the structure of the torso). I hope you don't mind if I save them, they are very effective diagrams! :)

These look great! If you're having difficulty visualizing something try breaking it down into different 3d shapes. Try inventing the shapes yourself then go out and see what other artist do.

Incredible

Hi Rob, you have a really good way of suggesting shadows without compromising the readability of the structure: really simple and effective, you can see that you have a clear idea of what you are doing! Your studies seem to me to be good and accurate, especially the figure in the lower right of the third sheet, where you have expressed the shapes very well despite the tricky pose. There are just a few problems with the proportions, here and there, especially in the heads, but since these were the abdominal exercises, I'd say it's definitely not a big issue, you could have simply suggested the shapes and I understand very well that you went further for personal pleasure, which is fine (I would do it too, in a much less harmonious way than you did!).

so nice and clean. very cool.

Great Studies Nice shadow mapping, nice faces, everything looks very clean and communicates well. If I have to nitpick, I would like to see you balance more straights and curves. Some times I feel that you use too many straights and stiffs a little your gesture, But again, great work. Best regards