I don't understand this whole "arm getting tired" thing. Your legs and your back should be tired.
Arm is not supposed to be using much muscle to swing the racket. Yea sometimes you get jammed up and don't have time for a full take back but that shouldn't happen on most strokes.
Pure Control Tour: leather+og, 5g lead up top, 16L poly @ 52lbs = 12.68oz