Why burn yourself out? Why risk sparring if you have had a less than productive day or not hit certain targets? Why risk injury if your day has not been 100%?
Yes there is .. Once it starts, it will effect the nervous system, then thats followed by bad hormones dumped into the body. Followed by muscle loss and injury .
I really don't think ovetraining is a big deal unless it injures you, prevents you from training at a high level during camp or makes it where you can't recover in time for the fight. As long as you rest enough the days before the fight, I don't see how them sparring yesterday, 24 days before the fight hurts
That's essentially it, the inherent danger of peaking early. It wouldn't be a matter of sparring a day before the fight per se, it would be a matter of hitting your stride in the gym (wasting it) and continuing to go hard, plateauing and then burning out with your wad blown come fight night. Not something that happens overnight, in other words. Coaches monitor the rising & falling action in camp very closely for exactly that reason. You want to hit that window. Just like cooking. Over's as bad as under.
That makes complete sense of course, but then how do they improve and reach a new peak, especially with a young fighter? Lets say a fighter can run 6 miles a day at a 5 minute per mile pace, can spar 12 rounds throwing 100 punches a round, while punching at 1,000 psi. (don't get caught up in if these numbers are realistic.) He reaches this shape with 3 weeks left in camp and his trainer realizes that's his peak, so he tries to level him off. What if he can push him though to reach a new peak of 6 miles with a 4:50 minute pace, average 105 punches a round and punch with 1,100 psi? As long as he's well rested and recovers by fight time, isn't that good?
Yes, that's good, provided the rest & recovery is there. ...and therein lies the rub. A human body (even that of a prime gym rat world class athlete) has limits. One push too far seeking a new peak, and you can leave someone totally deflated.