Hello! Here are some backs I drew the other days, I don't think they're showing up in the critique requests so I'm trying again (apologies if you've already seen it) https://line-of-action.com/art/view/4766
Lookin good! I would recommend studying muscles and bone structure since some of the muscles look like they could be mispalced on some of the backs. Backs in general can be tricky since we don't really look at them as much as faces or hands. Great work so far!
Love how you understand your back anatomy, that's extraordinary.
If I can suggest you a recommendation, then it would be to sketch out the same backs, only in 27 minutes of 30 second poses, please? The reason why is because, your backshots will be even most cartooniest and expressive in gestures and poses.
Love them! Honestly a bit jealous. The line quality and shading looks great. The only criticism I think I have is that the arm on the far right corner looks a bit flat, and could use more curves of muscle contour like the rest. Other than that, they're great!