That explains a lot. One of the true and tested recipes for libido suppression the Church takes to heart is to physically and mentally exahust their horny young men until they are not horny any more.
This of course is just my opinion, but an informed one. I went to a Catholic mid-school and highschool, and even when we were not 100% on board as a seminarist would be, sports was something the administration promoted very heavily. We'd also get to know lots of seminarists that would come to do field work there prior to taking their vows, and an almost universal trait of them was their passion for sports.
Now you're making sense. For someone who's not been doing serious long distance running since childhood, 20 miles in a week is quite good. From what I've read in running magazines, and personal experience, doing much more than 30-40 miles a week is not good for your body (esp. knees). 100+ miles per week is crazy.