Imagine you've got the following runner:
He runs a 20 min 5k without training, starts running 40-50 mpw
and runs a 16 min 5k in less than a year of training.
Then you start upping his mileage, but no matter what you do, no matter how slowly you build up,
if he goes over 60 mpw, he get's an injury.
This cycle of upping mileage en getting an injury repeats for 3 years, and he only improves to a 15:30 5k.
You know he has the potential of running sub 15, maybe 14:30. How would you get him there if you can only get him to run 50 mpw (or say 6 hours/week), without an injury?
PS: Ped's aren't allowed