Terenzo Bozzone is, and I have this on good authority - or at least on the authority of his very good PR person - a "gorgeous cheeky young upstart". Would I like an interview? "We're working the 'boy-to-man' angle, how he has come through from being a teenage sensation and is now up there with the best at only 25!"

Well, why not? I must admit the sensation of his teenage years had passed me by rather, although I do vaguely remember that he was on Celebrity Treasure Island. "We're trying," said his PR person, "to take Terenzo more mainstream".

So, he is, in case you're not an avid follower of extreme endurance sport, a triathlete who, on March 5 in Taupo, will take on the Ironman champion Cameron Brown who has won that race nine times. It is of course the upstart's great ambition to unseat the champion.

So you'd think he'd be a bit too busy training to do interviews, but he has been called a "superstar" in the making and that making involves profile.

He turned up wearing what is presumably "mainstream" garb, which means a shirt sans sponsor's logos. But he was carrying a shirt with sponsor's logos. Which would we prefer for the pictures? Without, thanks. He said: Could I say that he'd asked?

He talks about success in his sport as having to be "the complete package. I guess you have to have the profile. You've got to be marketable." To be marketable you have to be able to convince sponsors that you can persuade people to use their products and you do this, in part, by having a high profile on Facebook and Twitter.

There is an internet rumour that he Tweets while racing, which must be baloney. He tried to convince me that he has a special gizmo on his iPhone to make it waterproof. "Of course! It's all about your fans." He has, he thinks, 5500 followers on Twitter and 7000 on Facebook.

What an exhausting life he leads. A day's training might be a 200km bike ride then a run of 20km straight away afterwards, and then he has to keep his profile up. If you don't have sponsors, you can't afford to compete. So he has to keep the sponsors happy.

I said that he should arrive at interviews wearing his sponsor's shirt then, and not give people like me the option. Truly, I was only trying to help. And if he's cheeky, he should be able to take a tease, but he said, a bit huffily, "do you want the guy who turns up in the sponsor's shirt and every second line is [some sponsor's names]? Or do you want to interview the guy who just drops it into the conversation subtly?"

He seems to have had a preternatural sense of his image, but presumably he had to, to attract those sponsorship deals. He went on Celebrity Treasure Island at the tender age of 19. Because of a desire to be a celebrity? "Aah, no." Well, it is called Celebrity Treasure Island. "Well, then I must have already been a celebrity!" The Treasure Island experience had a bit of a sour aftermath.

He said that "none of the media talk to me about that", meaning, I suppose, that he didn't much appreciate me talking about it. The short story is that he turned up, in Portugal, straight after filming the show, to defend his world junior triathlon title and, during the bike leg, stopped to help another New Zealander who was having an asthma attack.

This was not regarded as a selfless act by some of his teammates. He was lambasted for his lack of preparation - the accusation being that if hadn't gone off to be on the telly, and thus hadn't put his profile ahead of his training, he'd have been fitter and nearer the front and nowhere near the ill rider. He was then accused of playing up his good Samaritan role. He said, "where did you find this info? Have you been stalking me?"

I was trying to get at why it all got so messy, because the bones of the story make it sound as though he was really disliked. "I guess people thought that I was trying to get media attention but the fact is I didn't say anything to the media ... I was 19. Yeah, it was horrible. I guess I was seen as a bit of an outsider. It was hurtful, but I didn't care."

As he says, he was only 19, which is awfully young. At 25 he is still awfully young in some ways. That "but I didn't care" is a young man's bravado, I think, although perhaps it was also good training for the emotional rigours of Ironman. He also makes terrible jokes, which no experienced superstar athlete (except Shane Warne, perhaps) would make to a journalist.

One of his jokes was that he liked his coffee the way he liked his women: "long and black". His girlfriend, Kelly, who is by the way, very good to him and makes his protein shakes and his lunch and his dinner - "I wash the dishes!" - might be a bit cross with him. "No. She knows I talk shit."

He was very good - "I haven't been too bad, have I?" - about not talking triathlon jargon. I started it by asking what red-lining is. It is, he said, like when the rev-meter in your car goes into the red and you know if you stay over the red line, the car will blow up. Goodness.

There is another condition called "bonking", which is when you haven't had enough calories and you start going dizzy and wonky in the head. This doesn't sound much fun but perhaps the least appealing aspect of the Ironman (or woman) competition, but one I imagine people want to know about is: how you go to the loo?

How do you think? His coach runs simulations in advance of big races and, in what might be regarded as a brutal form of toilet training for adults, there is a penalty on those who succumb to diarrhoea: they have to turn up to the race registration wearing Speedos and compression socks. He says he would never go in his race kit, because it's white. "I would probably lose a few fans." (Peeing is fine, apparently; everyone does it in a sport not for those squeamish about bodily functions.)

I was about now trying to work out whether Ironman is a sexy sport. "Oh yeah!", he said, "haven't you seen pictures of me in my lycra? I think it has a lot of potential. There's no fat people. Sorry, that might have come across wrong. Everyone is healthy. They care about their bodies."

He talks about his body as his "money maker. And if you're ruining your money maker, you're ruining your temple. You've got to be smart." He doesn't eat a huge amount. "Not overly. I've got manorexia." I thought this was one of his jokes but he said, "most endurance athletes do. Well, not in a bad way. If you look at long distance runners, from Kenya. The lighter they are, the faster they go. They're skin and bone."

He's180cm tall and his perfect race weight is 70kg. It goes without saying that Ironmen have to spend a lot of time thinking about their bodies. He had the best excuse I'm ever likely to hear for changing an interview time: he'd had to go and work on his "glutes". I wasn't sure what glutes were but now I know that they are your bum muscles, and his don't work properly. I was amazed to hear this. He said, "yeah, you wouldn't think so by looking at them! Ha, ha. Sorry."

He ought to be weird. I did a bit of reading about Ironman people before going to see him, and some of them are very strange, as you'd expect. I asked if he'd ever heard voices, because I'd read about a chap who heard the gods talking to him while doing the most gruelling of all: the Kona race in Hawaii. This seemed to me to make perfect sense. He looked at me as though I was the one who was nuts. "Not if you're a sane person!" he said.

He said, "I love pain!" Most sane people don't. "Pain is temporary; victory is forever!" He is, of course, fiercely competitive, and much of that competition is with the pain. I asked him to describe what that feels like and he said: "Your heart feels like it's going to come out of your mouth and your lungs feel like they're too big for your chest and your legs feel like they're going to explode." And he loves that? "You know that if you're at that point, something special's going on."

Other than that, he's not particularly weird, although we did have one very strange exchange. He said, "I want to be the Lance Armstrong of triathlon." Lance Armstrong seemed an odd choice, for obvious reasons. "Have you read his book?" he said. No. "Have you read his book?" he asked the photographer. No. He was truly flabbergasted. "You must be the only two people on earth who haven't read his book!"

He means on his earth: which is Planet Ironman. So, considering that he had just spent an hour of his day talking to a resident of that alien place called the mainstream, he didn't do too badly. He is trying very hard (a bit too hard probably) to be that total package. I don't envy anything he does for a living, but that least of all.