The most extreme and messy challenges on Radio 1

The human spirit is a heroic thing, particularly when tested by circumstance, and Radio 1 likes to put that theory to the test. It is in this spirit that Charlie Sloth sends rappers hurtling round the rally track. It's in this spirit that Nick Grimshaw wires celebrities up to a machine to measure their heartbeat and then asks embarrassing questions, and it's in this spirit that Greg James set off on his bike to conquer the UK, only to pedal headlong into a snowstorm.

Poor Margot Robbie. It's bad enough being filmed talking about embarrassing stuff while rigged up to a heart rate monitor. Or at least, it probably is. Most of us can't possibly know what that's like, but it sounds bad enough. In any case, Margot had the extra burden of trying to play this mortifying parlour game while trying to shake off an epic hangover.

Just watch how everyone reacts to the first spike in Margot's pulse rate. It is literally not for the faint hearted.

The concept of Charlie Sloth's Xtreme Bars is simple - to put rappers to the test by seeing if they can remember the verses to their biggest tunes while being driven at speed around a rally track.

There are penalties for flinching or delivering their words with less than 100% conviction - as Big Narstie does while attempting to rap and keep his terrified eyes open - and if their flow should stop for any reason, that's points on their rap license.

Innuendo Bingo is the messiest game on the radio. Scott Mills invites celebrities to load their faces with water and listen to carefully selected clips from TV and radio that might, if you were of a certain frame of mind, sound dirty. Their job is to try not to laugh, and therefore squirt a gobful of water over the entire room (and co-host Chris Stark).

Pixie Lott and Anton Powers teamed up against Chris, and failed so spectacularly in holding back that he ended up drenched from the first clip, and things only got worse from there.

For Charlie Sloth, Sideman is like a knight in shining armour, in that he is often sent away on quests, like the time Charlie made his partner in rhyme bring back three items he got from people on the street without buying them or borrowing them.

But perhaps the most extreme Sloth challenge to date was the time Sideman went to the Boat Show at Earl's Court in character as a Jamaican dancehall MC called Sweetcorn. His mission? To try and secure a big bottomed yacht for his music video.

This footage from 2010 has a strangely dreamlike quality. There's the pre-buzzcut Katy Perry and Scott Mills in a white room with a guitar, a stepladder, swingball, balloons and various other items including Strictly Come Dancing's Brendan Cole. And we can't hear what they're saying because of the triumphant classical fanfares playing while they wander about, being ordered what to do by the Radio 1 listeners.

The messiest bit is definitely the pottery, requiring both Katy and Scott to don plastic bodysuits, which, to be frank, do nothing to reduce the fever-dream oddness of the viewing experience.

Greg James put himself through hell for Sport Relief this year when his Gregathlon took him to the top of the highest mountains in Wales, England and Scotland, with a nice long cycle ride to each one. He started on Snowdon, cycled to Scafell Pike and climbed it, then attempted to ride on to Ben Nevis and climb to the top. And that would have been tough enough, but the weather took a turn for the worse - in fact he ran into the Beast from the East, a weather front containing the worst blizzards Britain has faced for decades - and on his first attempt, Greg had to reluctantly stop the challenge.

Thankfully, he's made of stern stuff, and as soon as the snow had cleared, he was back on the road, starting the entire task again and completing it like a champ, raising a whopping one million pounds in the process.

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