I ran at an elite D1 collegiate program. The vast majority of runners will get injured at 100 miles per week, assuming a reasonable pace no slower than 7 min / mile. Slower than that is not useful training for Olympic events. Our top runner was a 13:30 5k and 29:20 10k at 70-80 miles per week.

Ultras are a different beast entirely, as its more of a "survival" test of muscles, ligaments, and bones than that of sustained running performance--even top ultramarathoners will walk during races. Ultras are about physiological limits of our bodies to handle stress; the 2-hour marathon is about the physiological limits of running.