Go to see how much time before Olympics US organized Marathon Trials in 1972, when Shorter won in München. Go to see how many marathons the athletes of 40 years ago were able to run in one year, but especially how much time they used in between, and you can see that recovery is something regarding the mental situation, more than the physiological situation.
What can do the difference is the motivation. A well trained athlete can recover 40 km submaximal in one week, and this is exactly what they do.
For example, 30 days after running in Boston in 2:03:06 his first Marathon, Moses Mosop ran in training 18 times 1000m with recovering 1'20", the first in 2'45", the next 16 in 2'42" and the last in 2'36", for preparing the attempt against the WR of 30 km (10 days later, so exactly 40 days after Boston), record that he bettered with 1:26:47, still the current WR.
The big difference is that training is part of the plan, and the athlete has total concentration not only for the session itself, but for what has to do AFTER that session. The Marathon race, instead, is the final act of a long period of total concentration, and the athlete, after the race, needs to mentally relax (not depending on the fact the final result was good or not : the race is the final station, while 40 km in training are an intermediate station).
Another thing is that the practice to have several sessions at high intensity can make for the athlete more easy to recover in short time, making his effort something usual. On the contrary, more comfortable training, with lower level of intensity or lower volume, can preserve energy, but at the same time have a very higher cost for body and mind when the athlete needs to express himself at the max level, during a competition.
There are no other ways for reaching the best personal potential limits.
Every other system can only bring athletes NEAR that level, but never they can reach their best.