That is definetly do-able, though i'd question the effectiveness after a certain amount unless he is doing different types. A mate of mine does 400 a day minimum and is 6'7", i reckon he will **** his back up pretty soon.
Herschel does 3,500 sit ups a day. Walker is also crazy. No, he really is crazy. He suffers from multiple personality disorder. He claims he doesn't even remember what year he won the Heisman. Check out this article on him. http://www.cnn.com/2010/HEALTH/10/11/herschel.fitness.martial.arts/index.html This guy is damn near 50, is a vegetarian, eats once a day(sometimes he goes 3 or 4 days without eating), and is still 6' 1", and 221 lbs. of muscle. I don't think he's human. Either that, or maybe one of his other personalites are the ones who actually eat and get protein in his system.
Your core can take an almost unlimited amount of work everyday, it's not like your other muscles. Though it is possible I can't imagine it's true without his back being incredibly sore, he must mean variations of sit ups, like biking on the ground, leg raises, reverse sit ups... If he were just doing that many straight sit ups I think he'd be in some pain.
But seriously mrjotat? You thought this was worthy of a new thread? Like you were exposing some big cover up?? atsch