You've got the overall pose down really well, proportions are good although the legs look a bit short and the top of the head got squashed a bit. I'm not sure if you're going for a deliberately cartoony look but if you aren't, you could try adding more curved lines, particularly on the limbs and back. It would make figure look more fleshy and muscular.
(BTW, thank you a lot for including the reference picture! It's super helpful for critique-writing.)
(BTW, thank you a lot for including the reference picture! It's super helpful for critique-writing.)