equinoxx is quite right in some respects, but his edit loses the balance of the piece.
By all means ignore these suggestions, as I can see yours is highly stylised,
BUT (in my defence) regardless of that - some understanding of the underlying form is required - stylised or not... you asked for anatomical help so here goes...
You need to maintain balance - but
not by leaning the character over (as illustrated by equinoxx [sorry dude]) :S, but by twisting it. I've done this (very) rough edit in a bid to demostrate what I'm trying to point out.
The shoulders and the hips counter each other, one leans one way whilst the other leans the opposite - the scapula in the back are in slightly different positions according to the weight distributon and tension caused by the heavy axe. Whilst the deltoids in the neck are more prounounced - thus lending more feeling of weight on the axe... I dunno why I changed the axe head I just thought it looks more brutal this way...
Generally I've enlongated the body to accomadate where the thoracic cavity would be as well as the pelvic girdle and section in between... I've also illustrated where the gluteus maximus would roughly appear (the arse muscles) as this seemed to be missing for you intial sketch.
I've tried to keep it kind stylised...
I'll be interested in seeing where you take it...
good luck
EDIT - I just noticed you were looking to make it menacing...
Try hunching the character further over (like a gorilla)
Here -