Guys like Mike Wardian have some strange ability to run 2:2x marathons in back to back weeks. High school kids can somehow take a constant beating from bad coaching and run good races. What exactly is going on in their body that allows for this to happen? I'm a relatively light guy in my mid 20's and it's not the pace that gets me, it's the constant pounding that leaves me with bone and muscle damage that takes a long time to get over.
Naturally high levels of testosterone and other hormones, coupled with good biomechanics, mean they break down less, and recover faster.
I'm convinced the ability to recover is what constitutes "talent" in distance running.
I see some of the NCAA's best training (I watched C. Derrick do a sub 29 6 mile tempo in August on rolling roads and called it an 'average' summer tempo) and they simply can do more work that is faster and harder and bounce back quicker than my mortal 25:00 ability can get me to do.
It depends how hard the race or training session was and how your training build up went.
I can be on a roll for months, training and racing hard, with very quick recovery and then one day I will just give that little bit more and boom, I'm done, I need weeks to recover.
To get on a roll like that you need to increase the workload gradually and not try to do too much too soon. Then when you do have that exra hard race or training session that takes much longer to recover from, use your common sense and take it easy until you are properly recovered.