There's this one story where the MC, after absorbing Majin Buu and Frieza, went and beat up Saitama barely, causing Saitama to go into a daze. After a while, Saitama snapped out of it and declared that he'll do 200 push-ups, 200 sit-ups, 200 squats, and 20 kilometers of long-distance running every day from now on.