There are lack of back muscule structure, missing shoulder, right hand is short, fist is good to give a flowers, not for a hit - should be turned fingers down, strange lineart of left hand...
Check a general anatomy, it should help.=)
Setting your light sourse lower would make it easier to work on muscule texture.
Maybe smth like that - just for a clue, I've tryed to fix a bit but I ain't a muscule fan.=)