Looking at this shoulders and muscles for McGregor I cant think of anything else but him using some kind of steroids.
I do hope they will be testing them before the match.
I do hope they will be testing them before the match.
Or he could have focused more on shoulder and biceps/triceps during his training with metal
Or this was achieved due to lots of wrestle training 
From I cannot see the transformation to I can see the use of steroids hehehe.
In any case, @TopTort777, agreed that this new bulked Conor might be from wrestling. I speculate that we might see a different fighting style from him with more wrestling included similar to GSP style?