'People seemed to love us proving that the difficult was possible'

There are three questions that people always ask me. Can I have a badge? Where's John Noakes? And why do you do these crazy challenges for Sport Relief? For the last one, part of the answer is simply because I can. It really is as simple as that: why not?

Over the past three years, I have agreed to do things for Sport Relief that have seen me so bruised from falling on taut wire that I couldn't sit down; things that have reduced me to a diarrhoea-riddled mess; things that have left me lying on the deck of a boat so dehydrated I couldn't move a limb.

I don't expect sympathy. I put myself in those situations and I would do it again in a heartbeat. But I'm neither a daredevil nor an adventurer. I am just a Blue Peter presenter.

Since 2008, my job has been to excite kids about the world. Blue Peter prides itself on pushing the envelope and that's why, when I joined, my boss agreed to let me go to Africa and run 78 miles in a day.

I say "agreed" because I wanted to. I was 24, and learning that life throws things at you that aren't pleasant. You have your heart broken, you lose people, you get hurt. In my simplistic head, I thought if I could complete an ultramarathon in the desert, I'd be able to deal with anything life throws at me. I wanted to find out something about myself. Adults pointed out I was a non-runner – but the audience believed I would cross the line in a mere six hours.

That was how this "challenge" thing started. The run caught the eye of someone at Sport Relief, who tapped on Blue Peter's notional door and asked me to do a new challenge. I didn't have a clue what I was letting myself in for when I agreed to attempt to kayak the Amazon. I'd never been to the jungle and I couldn't kayak. There were plenty of naysayers, but no one could give me a reason why I wouldn't be able to finish. They just said it would be hard.

The reason I got through it was because of Sport Relief. My job was to "capture imagination": to raise awareness and get people to run the Sport Relief mile. If I can go the extra mile, so can you. In my head, if I suffered and struggled and put up with a bit of a pain, I could look the people I meet at Sport Relief-funded projects in the eye and say: you might feel at rock bottom, but it might work out OK.

I learnt from the ultramarathon that kids put a lot of faith in you. They are willing to believe you until you let them down – and why would I let them down. I had proved them right in the desert and that's why I had to make the Amazon a success.

It was stressful, but I came back to overwhelming support and the realisation that no matter what your experience, anything is possible if you give it a go. The messages I got from kids made me cry. And that made me want to do more. People seemed to love us proving that the difficult was possible. So I've carried on doing these challenges, because the audience seem to like it, and it's become what I do.

We did the high-wire because it was different: a stunt rather than endurance. Trekking to the South Pole gave us a chance to deal with a different and more challenging environment. Each time, I agreed through sheer naivety. But if I managed to raise one kid's expectations – of themselves and of others – and raised money for a charity I believe in, then I had made my day at work count.

Will I do any more big challenges? Part of me thinks I am getting a tad predictable, but a bigger part of me loves the fact that, increasingly, I get asked "What's next?" before the inevitable: "Can I have a badge?"

For the record, you have to do something for Blue Peter. And I believe John Noakes is living on a boat in Marbella.