I was always told to get used to fencing tired because if you ever do well enough to get to the final rounds you'll be tired anyway. (not that I'd know the way I fence, but I'm 28 and know the days are numbered that I can let youth compensate for laziness and get away with it).
This is more mental than physical but one my coaches favorite--and oft repeated--statements is that if you are in that final bout you're going to feel wiped out and sore the next day whether you get first or second so you might as well fence hard and get first to compensate for the pain.
