I'd lower the crotch a little. The legs looks pretty good in shape. The arms seem to rigid, I think, that looks like the problem to me. Look at some photos of people standing in a relaxed position, and maybe go from there? They are also probably -slightly- too short.

Thank you for your comment !

I used a ref from posemaniacs but I didn't find a standing person like this, so the proportions may be off, yes^^'.

I'll change what you said, but my biggest problem is the position of the arms, I can't get it right.

EDIT : Updated. Don't know if it's better. More critics please .

I like the general torso area, but the head seems like that of a baby- way out of proportion when compared with the rest of the body. Try making it smaller. The upper legs look fine as well.

The arms are too thin when compared to the legs- thicken them, and maybe add a lighter shade to the lower part to make them seem level with the pelvis in depth. Also, a little work on the feet could help- they need some anti-aliasing on the inner areas, which you could do easily wtih a few pixels of a darker color. The lower legs could use some thickening as well- they look like they might snap.