From wikipedia:
Although described as "a bit on the husky side", to maintain his health while indulging for the show, Richman exercises twice a day while he's on the road. When the schedule permits, he does not eat the day before a challenge and he tries to stay "crazy hydrated" by drinking lots of water or club soda and forgoing coffee or soft drinks. After taping for a challenge is complete, Richman spends an hour or so on a treadmill, telling the Las Vegas Review-Journal, "Being sedentary is incredibly uncomfortable. [...] espite the fact that the first 10 minutes or 15 minutes on the treadmill might suck, it actually does alleviate a lot of pressure, and you feel better."
Re: planking and running, I've seen mixed comments about whether it helps or hinders running form. It makes your abs look better though.
[when used in conjunction with other core exercises, blah blah...]