With his leading role in Ninja his line delivery was rough and blunt. Adkins is like JCVD minus the swagger. It's difficult to watch at times outside of the fight scenes. The cadence within his line delivery is the real issue, it's too flat and matter-of-fact.
He's alot like Dolph Lundgren.
Although I haven't seen any of his other movies where he has lines (aside from Undisputed 2 & 3). Usually he's stuck as stunt coordinator or just there to look good. Tough guy extra number four or something like that. But it's easy to look past the faults in his acting ability when you get fight scenes like this.