O'Leary in dance marathon training
X Factor host Dermot O'Leary has admitted that "reality has set in" over his 24-hour dance marathon.
The TV host, 41, will begin his moves at BBC Broadcasting House in London before finishing his challenge by dancing down Regent Street and into the London Palladium, where his efforts will be screened on live TV.
O'Leary told Radio Times magazine that he texted Comic Relief founder Richard Curtis with the idea for Red Nose Day after dancing for six hours in Ibiza.
"Initially, I thought it sounded like a lot of fun, but two weeks ago, reality set in and it started to sound like an endurance test," he said.
"No one's really done it before, so it's hard to train for, but at the moment I'm doing a combination of running and dance lessons for about eight hours a week. I'm in a perpetual state of lactic acid coursing through my veins."
He added: "I'm determined to keep moving non-stop - though I've requested lots of indie, shoe-gazing music to make sure I can slow it down a bit. And if I'm not actually dancing, I'll be seat dancing!"
O'Leary said that he would "try something that involves some kind of technique" once an hour, but for "the rest of the time it's just about keeping those feet moving".
Curtis told the magazine that he was not impressed with O'Leary's fund-raising plan at first.
"My first thought was it's a terrible idea, because it's a pretty well-established fact that Dermot O'Leary can't really dance.
"He has one signature move, which he has performed at the start of The X Factor every week for the past eight years," he said.