God I fucking hate Loomis so much. I hope in another 3 or 4 years people stop referencing his book so much like its a fucking beginners art bible.
Ok I think your three MAIN problems are this:
1) You dont really have a sense of the anatomy, and by this I mean you dont really UNDERSTAND the form. I can tell you know that the biceps has 1 shape, and the triceps has another contrasting shape. I can see you know how the clavicle runs almost "into" the deltoids. So I'm fairly certain you have some degree of knowledge on anatomy (albeit a bit basic, but good enough!). But knowledge of WHAT is WHERE isn't the problem (imo). Its more like now knowing what the form of what your drawing essentially IS.
Sure the pectoralis muscles are squarish/pentagon-ish in shape, but they're MORE than that in FORM.
2) Line quality. You're line quality is exactly of what I would expect of someone prolly in Middle school-High school. Its scratchy and relies on darkening lines after the fact to reinforce clarity. I would say one of the best way to get rid of this is to stop using pencil for a bit. What I did to overcome this is ONLY use liner pen to draw.
-It makes your marks permanent.
-It makes your marks solid
-It forces you to master a new tool
-it helps you think about what you're putting down first
What you might try doing too is limiting the amount of strokes you use. Like say, you have 12 strokes to make a person. (this REALLY forces you to think about what your're doing). I'll be the first to say that art is as much a mental game as it is a practicing skill. You observe/analyze, You internalize, You interpret, THEN you practice.
3) Repetitive subject matter. I really can't tell one figure from the next in a lot of these. Its a lot of Same face, Same body type, same poses, same hair, same etc. Push those boundaries man. Maybe draw a woman once or twice, or draw a fat guy, or draw a child or old man. Make it a guy with a beard, or maybe some asian guy with a large forehead (idk), but explore a bit. You're still young take a few steps out that comfort zone. Maybe draw in a style you've never tried before, just break the mold sometimes dude.
EDIT: Also try not to worry about anatomy allll the time, your figures feel still because you're thinking too much about structure, not letting it just inform you as you go along. You gotta feeeeeel the pose. feeeeel the tension. feeeeeeeeel the graphite~
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god i fucking hate loomis.