I run ultras and mountain races. I ran one this Friday night into Saturday morning - a 12 hour overnight trail race where I managed 100K (62mi) in 11 hours and 23 minutes. Anyway, let's throw out willpower and even genetics for a second so I can bring up something: In today's age, virtually no one is even remotely close to their physiological limits. Literally, hundreds of people (elite marathoners, a few ultra marat…
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.