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To me everything looks really... rubbery, I might say. Way too bendy at least, and the foreshortening on the legs (which I assume you tried) doesn't really work for me and he looks like he has really short legs (or overlong arms and torso that don't seem to share the foreshortening). Also some of the things just don't seem to work together, like the way his chest muscles are angled is completely different from his ribcage to a degree that's physically impossible without having his muscles be completely detached from his skeletal structure.
And lots of things (his hands for example) look flat and not referenced.
What did you use as your ref for this?
His cape makes no sense either.
Yeah I'd suggest getting a proper ref for the actual pose. Divers, gymnasts and pole vaulters are pretty good subjects to study (even though photos of them may have forced or lack of natural perspective) and just posing yourself and taking photos will help.
Also, when choosing the pose for something like this, I'd pay in mind to keep the action line clear and the pose fluid so that it can be used to lead the eye. Right now your pose is more like a a half-circle that points back to the left corner of the image.
(Here's my example, mind you it too is full of perspective/proportion/anatomy problems)
And couple example refs: