It’s 10am and Michellie Jones has just returned home from a three-mile swim, and is eating oatmeal for breakfast while sipping an energy drink.

She will soon leave her house again to spend the next six hours on her bike tearing across the hilly countryside surrounding San Diego, California. If she’s in the mood she may finish off with a run.

It may sound a bit over the top, but then nobody said winning the toughest race in the world was going to be easy.

On Saturday the crystal blue waters and sun-kissed beaches of Hawaii will feel like hell on earth for Jones and 1,800 other elite athletes who will be competing in the Ironman triathlon world championships. Competitors must swim 2.4 miles, cycle 112 miles and then complete a 26.2mile run, all within 17 hours.

The Tour de France may cover more miles, and there are longer races, such as the six-day Marathon des Sables across the Sahara desert, but in terms of sheer bloody-minded endurance it is an event that takes some beating. Jones, 38, won the women’s event last year and is hell-bent on retaining her title.

At stake, alongside £54,000 in prize money for the male and female winner, is the opportunity for both athletes to call themselves the No 1 Ironman in the world. There are thousands of triathlon events around the globe each year, but none is as prestigious, nor as popular (it attracts more than 25,000 spectators and more than 50m people watch on television), nor as physically demanding – the Ironman triathlon is four times longer than the version of the triathlon that is raced at the Olympics.

The conditions, where temperatures reach 95F, compound the competitors’ exhaustion. “It’s hot and humid and the winds are so severe that you can be thrown off your bike,” says Jones, wincing.

“I’ve been concussed like that before, and have even fractured my hip. You just don’t know what’s out there, so a big part of the race is that you’re battling against nature.

“So many things can go wrong, there’s never any guarantee that you’ll even finish.”

The start of a triathlon has been likened to swimming blindfolded in a washing machine as hundreds of swimmers kick, punch and scratch for position.

“It can get really tough because some people just don’t swim straight,” says Jones. “Once I was kicked in the chest and it tore my rib ligaments. Another time my eardrum was pierced by a blow to my head.”

Jones, who is from New South Wales in Australia, started competing in 1988, racing in shorter triathlons, and she won a silver medal at the 2000 Olympics in Sydney. Then, four years ago, she decided to try the longer distance and admits to having become addicted to the challenge.

“It’s such a fantastic feeling accomplishing what most people would see as an impossible task,” says Jones. “I never thought I wanted to do an Ironman, but there’s just nothing better than running down Alii Drive [the palm-tree-lined stretch of road at the end of the course] with the end in sight.”

The Ironman triathlon was conceived in 1978 during the awards ceremony for a Hawaii running race. Competitors began to debate which type of athlete was the fittest – runners, swimmers or cyclists – and John Collins, an American navy commander who was stationed in Hawaii, dreamt up the contest as a way to settle the argument. “Whoever finishes first, we’ll call the iron man,” he is reported to have said.

The record for the course is 8hr 4min 8sec, held by Luc Van Lierde from Belgium, the first European to win the men’s title, in 1996.

Jones’s best time is 9hr 18min 31sec. But in one respect the reigning female Ironman is still human. “I’m not a big beer drinker,” she says, “but I’ll definitely have a nice cocktail to celebrate when it’s over – because just finishing is an achievement.”

How to get started

Visit www.britishtriathlon.org to find a club

Start with the shortest version – 0.5mile swim, 12-mile bike ride and 3-mile run – and gradually build up

There are more than 400 events sanctioned each year by the British Triathlon Federation and InGear’s guide to getting fit for triathlon provides crucial tips (tinyurl.com/293fv5 )

To enter the world championships you’ll need to do well in an Ironman qualifying event. See www.ironmanuk.com for details of the next UK race

Competing in a triathlon competition is not cheap. A decent bike will cost from £500. You will also need a wetsuit, tri-suit (which goes under the wetsuit for cycling and running) and helmet. Then there are the extras such as a heart-rate monitor, while elastic shoelaces will save vital seconds in the changeover between swimming and cycling. And don’t forget the puncture repair kit