BBC Radio 1's Nick Grimshaw is to host his breakfast show from the saddle of a bicycle - as he pedals for 12 hours in a transparent box.
The party-loving presenter will be part of a breathless team of BBC radio stars aiming to clock up 25,000 miles by running, swimming and cycling for Sport Relief.
Radio 2's Jo Whiley is also due to put in a marathon effort towards the total by spending 26 hours on a treadmill - during which she will present her show.
Their feats will take place in a box positioned outside the BBC's Broadcasting House in central London, allowing the public to watch the stars as they are put through their paces and try to get through their programmes while undertaking their tough feats.
The idea of the challenge, BBC Radio Around the World for Sport Relief, is to match the distance around the circumference of the earth from March 17 to 23.
Grimmy will be joined by fellow Radio 1 and 1Xtra presenters, as well as brave guests, who will take their place on bikes alongside him. He will begin his 12-hour stint as he goes on air at 7am on March 17 and will finish during Greg James's show later in the day.
Nick said: "It's amazing to be doing a tough challenge for Sport Relief - although the last two times we've done sport on the Radio 1 Breakfast Show, there have been injuries. So hopefully this will be third time lucky."
Last week he joined pal Davina McCall, running alongside her for a section during the final day of her 500-mile challenge.
Jo will start her non-stop treadmill session at 8pm and will finish it at the end of her two-hour show the following day.
She said: "I'm extremely nervous yet excited about my challenge. It's going to be ridiculously tough, but the one thing I have to remember is that the money raised will be spent helping people living incredibly tough lives - that's what will keep me going."
Asian Network presenter Tommy Sandhu will take part in a cycle relay and at the BBC's base at Media City in Salford, Radio 5 live broadcaster Nicky Campbell will also be playing a part.
Presenters from other parts of the UK will also be involved including the BBC's Look North presenters Harry Gration and Amy Garcia who are to cycle the Yorkshire stages for this year's Tour de France on a tandem.