Tess Daly and Claudia Winkleman are battling injury and exhaustion as they try to complete a 24-hour danceathon for Comic Relief.
The Strictly Come Dancing presenters started the challenge on Monday night, and have been gyrating ever since.
“I’m not going to pretend it’s been easy,” Daly told BBC News.
“These guys won’t tell you how bad it is,” added Davina McCall, who was on hand for moral support. “They’re both in absolute agony.”
She explained: “Claudia is strapped up on her leg, both of them are strapped up on their back. Tess has been in tears, she’s also feeling nauseous, and Claudia is talking about baby giraffes.”
Their danceathon is being broadcast live on BBC Radio 2, and fans can watch on the BBC red button.
But while the duo sound perky and energetic on air, they slump in between appearances, taking hugs from colleagues and massaging their limbs without pausing their eternal shuffle.
When BBC News catches up with them in the 15th hour of their challenge, Winkleman is slurring her words and Daly is feeling “very sick”.
“We peaked a bit too soon, because we got really overexcited,” says the star.
“I bounced for the first four hours,” adds Winkleman, “and Trevor Nelson, who I literally love, came in and went: ‘FYI, you’ve peaked’.
“And I went, “Don’t be silly. I know I’m 47 but I can go on like this for 17 months.’
“About two minutes later, my knee clicked out, my back went out and Tess got sick”.
“But we’re going to keep going,” adds Daly. “We’re not going to stop.”
The presenters have received celebrity support from their colleagues at Radio 2, singers Fleur East and Beverly Knight, and the casts of the West End musicals Hair and Everybody’s Talking About Jamie.
Great British Bake Off winner Candice Brown, and former judge Mary Berry, also turned up at BBC Wogan House with sugary snacks to keep the stars on their toes.
This feat of endurance is all in aid of Comic Relief and, by 11:00 GMT on Tuesday, Radio 2 listeners had already donated £246,000 to the charity.
“Before we did this we went to see extraordinary projects that Comic Relief is supporting, so it was important to us [to do this]” said Winkleman. “The tiniest amount of money makes the most enormous difference.”
“Every penny will go to some of the most vulnerable people living in the most challenging situations in this country and abroad,” added Daly.
The challenge is due to finish shortly after 19:15 GMT on Tuesday night; but the stars say they might not have any energy in reserve for a “big finish”.
“Angela Rippon told us to save everything for a cha cha extravaganza at the end,” said Winkleman.
“I don’t know what to say about that.”