..Ok actually I've just been to the gym and tried the one arm seated row machine building up the weights to 50kg and it's not too hard.
So I reckon Nate must have had each side of the row machine loaded with at least 75kg instead, because his traps muscle are seriously huowge.
The boy knows how to train! - by observation that is at least 50kg loaded on each side of the back row machine. Correct me if wrong.
This video shows one of the best examples of how huge Nate Morton made himself.