'Neither of us have burst into tears quite yet,' says Katherine Poole with a certain pride. 'But there have been moments when I've certainly thought I couldn't go on - when my feet, my legs, my lungs, all hurt. But you dig deep, and push yourself through it.'

Pushing yourself to the brink of tears might seem like a strange way to spend your free time, particularly to those of us whose weekends revolve around TVs, takeaways and general economy of movement. But to Katherine, 35, a dance lecturer from Cheshire, and her husband Mike, 37, a primary school teacher, inactivity of that sort doesn't appeal.

The Pooles are devotees of adventure racing, and choose to spend their free time running, cycling, kayaking and navigating their way through the British countryside. Adventure racing grew out of events held in New Zealand in the early 1980s, but has recently mushroomed in popularity.

Its first incarnations were the huge 'expedition races' like the Raid Gauloises and the Eco-Challenge, which seized on the idea of combining many different disciplines into one, multi-activity sport. These races pitched teams of competitors against each other in wild, far-flung destinations like Borneo and Patagonia.

Soon smaller competitions sprang up with the same idea. Mixed teams of between three and six had to navigate over long distances, using various means of transport from bicycles to zip-lines, and this became known as adventure racing. It catered perfectly for the modern-day urge to escape the predictable rhythms of daily life, and rediscover the forces of nature. Clearly there was something about the sport that appealed. The number of races and participants grew, and, in the UK, the sport caught on massively. It is estimated that there are now more people racing in this country per capita than anywhere else in the world.

One of the UK's best racers is Tom Gibbs, 29. At the level he competes - often in non-stop races, held over many days, where he survives on less than a couple of hours' sleep a night - adventure racing is exceptionally demanding. But Gibbs, who teaches navigation and racing skills at training weekends, assures newcomers to the sport that everyone starts off at their own pace. 'Fitness levels vary hugely,' says Gibbs. 'One guy in the last training group was overweight at 18 stone, but he did very well. The point is that whatever your level of fitness, you can still compete and enjoy it.'

The Pooles' introduction to adventure racing five years ago was certainly relaxed. 'In our first race we actually walked rather than ran,' says Katherine. 'There was a four-hour racing section, and I thought, "Run for four hours? I don't think so!" During those first few races we did a lot of nature spotting. To enjoy adventure racing you don't have to be at the top of the field. You can set your own personal goals. When we started, we'd see if we could run for a few miles, and build our goals up each time. But you learn that you can do much more than you think, and that brings a real sense of achievement. I can look back now and get a real buzz from seeing what we've both achieved.'

The emphasis in adventure racing on mixed-team events allows the Pooles to compete as a couple. 'It might sound twee,' says Mike, 'but adventure racing is something Katherine and I can enjoy together.'

Another side of the sport that gets the Pooles out there training every weekend is the fantastic surroundings. 'We've realised how much amazing countryside is out there that we didn't know about,' says Katherine. 'My favourite place is the Lake District, and because you're out running very early you see it in a different light. Heaven knows, I'm not an early riser, but coming out here is a constant reminder of how beautiful this countryside is.'

Those taking up the sport won't face an excessively long or pricey shopping list. A beginner's equipment consists of a good pair of running shoes, a basic running kit of shorts and a T-shirt, and a cold-weather option of a pair of tights and long-sleeved top. Windproof and waterproof jackets are also a good bet.

Canoes or kayaks will normally be provide for races involving a water section. If you are set on buying a mountain bike, there's no need to go for a top-of-the-range model. A cheaper, rigid-frame bike will do. In fact, many races are geared towards beginners, and give competitors the option of hiring equipment for the day. The races are always well organised and safety risks are kept to a minimum. 'Marshalls are dotted around and they make sure you're safe and give you encouragement,' says Katherine.

Now the Pooles want to pack their racing kit and head overseas for some of the big, international races. For Gibbs, these have provided his most memorable racing experiences. 'You go to places that most people never see,' he says. 'On the Eco-Challenge race in Argentina in 1999, we tracked up a 11,500ft dormant volcano, and that was straight after paddling across a white-water lake. Earlier on we had been horse riding through the Pampas. It's a stunning way to see a country.'

Expedition races such as the Eco-Challenge cater to all levels. So while Gibbs will go to Fiji, later this year, hoping to be part of the first UK team to finish in one of the top positions, beginners' teams are also able to participate. 'This is the next generation of adventure holidays,' Gibbs says. 'You go and see fantastic scenery, and get further away from civilisation than you would have ever thought possible.'

One-horse race

Anna McCormack is one of the UK's top adventure racers, and now she's gunning for international success.

'I had a very lucky introduction to adventure racing. Two years ago I found myself in one of the biggest and most beautiful races in the world. I was a last-minute replacement for a team going to Nepal, to take part in the legendary Raid Gauloises race.

'A female member of the team had dropped out. I'd never done an adventure race before, but I'd lived in Nepal for two years, and done a lot of mountaineering out there, as well as mountain biking and white-water rafting. I received a phone call saying: "If you don't say yes in the next four hours we don't have a team." The other team members had to put in their visa applications that night. I've got nothing to lose, I thought, and neither do this team - so why not go for it?

'We covered 900km in total, by white-water swimming, trekking, canoeing, rafting and biking. The winning team completed the whole race in just under five days. We did it in seven. I was hooked.

'Since then I've taken part in a number of races. I won the Adrenaline Rush in Scotland last year - despite having to climb into an empty bag of fertiliser with my team-mates to avoid getting hypothermia. And I took part in the Southern Traverse race in New Zealand last November, with Sir Ranulph Fiennes. It was brilliant - he was the quintessential English gentleman. Nothing fazed him.

'For me what's really sexy about adventure racing is that you get a chance to compete overseas. Most of us never have the opportunity to go on an exotic expedition - but you can experience something similar in an adventure race. I also love the fact it is a very friendly, non-cliquey world - even the top athletes mix with the beginners.

'I race for Team UK Gore-Tex Packlite, and I believe that this year we can compete on an international level. We've got the best-growing adventure racing team in the world. We're moving up the ranks and one day we could have one of the best teams in the world.

'All the top teams have budgets of around £100,000 a year. Last year the UK team had less than £40,000. If we can find the sponsorship this year it will be the first time that the UK can compete on equal terms with the best: the US, Finnish and New Zealand teams. I have just quit my job to devote all my time to finding sponsorship for the team. At the beginning of the year, I'd only raced three times since last September because of work, and I'd had enough. I couldn't contemplate another year without competing, so from now on I'm a full-time adventure racer.'

· Anna McCormack will be speaking at The Outdoors Show, at the NEC Birmingham, 15-17 March

Racing in the UK
If you want to try adventure racing, training weekends are organised by Ace Races and cost £141, which includes accommodation, all meals, maps and the hire of a canoe.Trail Plus also organises races and training camps.

Races are held in the UK regularly. From 12-17 April, the Red Bull Northern Exposure race is being held in the Cairngorms, Scotland. Teams of four will compete for 72 hours, over a 120-mile course, likely to involve mountain biking, trekking, ascending and descending fixed ropes, canoeing, and three other winter disciplines. For information on the event, visit Red Bull Northern Exposure

Ace Races holds events around the country for all skill levels. On 11 May, there will be a one-day race in Thetford Forest, Norfolk, involving mountain biking, trail running and a selection of special team challenges. All competitors should expect to get wet, but a dry T-shirt and a hot meal will be supplied on finishing. The race is for mixed teams of three, and costs £99 a team to enter.

From March 16-18, the UK's first indoor adventure race will take place at The Outdoors Show, at the Birmingham NEC. The Renault Kangoo challenge will see 24 teams competing on challenges ranging from mountain biking to climbing, canoeing and tunnelling. There will also be a public competition where visitors can try an adventure race for themselves.

On the global scene
Two main international adventure races take part every year. The Raid Gauloises is the longest-running. Now in its 11th year, the Raid has been held all over the world, from Madagascar to Oman, and past competitions have involved events from orienteering, rafting and climbing, to camel riding, skydiving and sea-kayak navigation.

The Raid Gauloises adapts to the regions it passes through, so dep-ending on the terrain, competitors may be called upon to master canyoning or caving, and be expected to handle any form of transport, from a paraglider to a sailboat. This year the race takes place in Vietnam, from 27 April-9 May. Fifty teams from 17 countries will be taking part.

The Eco-Challenge is an annual, non-stop race, during which entrants compete for between six and 12 days continuously, across massively varied terrain. This year's event is taking place in October, among the 333 islands that make up the Fiji archipelago.

Competitors will navigate and trek over mountain ranges, and bushwhack through dense jungle to remote villages. For each stage, they will have to choose the best means of transport, be it swimming, mountain biking, river kayaking, fixed rope climbing or ocean paddling. Mixed teams of four will compete over nearly 500 miles, and there's £60,000 of prize money to be won.