Chrissie Wellington may have won four World Ironman Championships – the ludicrously tough 2.4-mile swim, 112-mile cycle ride and full marathon – set possibly unbeatable world records, have a handshake that can crush diamonds and be the closest living being to superwoman, but she is reassuringly approachable.

In her new autobiography, A Life Without Limits, she describes herself as an "accidental athlete". As we leave the house in a London suburb where she is staying (she is based most of the year in Boulder, Colorado) to walk to the park where she is going to put me through my paces, she says she still sometimes feels "like a fraud. Not that it has been easy, because I've worked really hard, but sometimes I can't believe it."

Listen to Wellington for a few minutes and you start to believe anything is possible, though I'm not sure I have ever met anyone as driven as her. She was a high-achiever even before she became an athlete, travelling the world, doing an MA in international development and working as a government adviser. But her discipline, drive and perfectionism had also led her down a destructive path: in her teens and early 20s, she suffered from bulimia and anorexia. She describes writing about it in her book as "quite unnerving. It makes you feel more vulnerable. It's easier if people think you're strong and somehow special."

Wellington's athletic career started relatively late – she was 30 when she turned professional in 2007. While her achievements might be remarkable, she swears they are not totally beyond the dreams of the average person. "I swam as a kid, but not very well. [As an adult] I started running 20 minutes at a time. I didn't grow up thinking I want to be world champion. Even when I started triathlon, I just wanted to see what I could do. Never in a million years did I ever think I would do an Ironman. Now I look back and think: what if I hadn't taken the chance?"

Motivation is my biggest problem and I don't think you could get any better than Wellington as a motivational coach. She has just produced an audio programme tailored to people training for a triathlon, but somebody less athletic can also gain a lot from it. "Your limits may not be where you think they are!" she cries during the bike programme, accompanied by a thumping soundtrack. "I want this to hurt!"

"I'm just trying to encourage people to test their limits and make them realise they can do more than they ever thought possible," she says as we start some hill runs. Wellington looks so graceful, moving on the tips of her toes like a dancer as I thunder alongside her. She likes adding a bit of variety to training. "Boredom can quickly set in if you run the same route at the same time. Vary terrains and gradients. Do speed work and strength work, like running up and down hills, otherwise it can get quite monotonous."

I am an instant-gratification seeker, and am disappointed when anything takes too long. "Often people feel they are not progressing as quickly as they want to," says Wellington. "Patience is key: the knowledge that the improvements you are making will make you stronger and fitter and that ultimately you will see the fruits of your labour."

By this point I'm getting tired and the familiar urge to give up creeps in. How does Wellington deal with this (for her, it might happen somewhere in a marathon, after miles of swimming and cycling; for me, it's after five minutes of running uphill)? "It's easy to quit but that memory of quitting will stay with you for ever," she says. "You've got to be able to override that urge and remember why it is you're doing what you're doing. Bank memories – that's what helps me get through a race, remembering times it has hurt and I've managed to overcome it."

I can imagine cycling around Colorado is a joyous experience, but she also fits in six swimming sessions a week and surely nobody likes doing lengths. "You kind of enjoy the pain and discomfort from working hard but it's not the most interesting," she admits. "But the ability to be in your own head and endure that monotony is part of being a successful athlete."

We run around for a while. "Relax your arms," she says. I'm finding it hard to keep up. "If you want to develop more speed, you need to go faster than the pace you want to race at."

When we stop she suddenly asks: "What's your goal?" I don't have one. "It's hard for anybody, whether you're a pro or a novice, to motivate yourself. You can only do that with a goal," she says. "That goal needs to be realistic, achievable, but challenging as well." I did a 5km race a couple of months ago – next time I do it, I don't want to come second from last again. Wellington beams. "There's your goal."

But actually, inspired by Wellington's no-failure, life-grabbing philosophy, I'm now thinking perhaps I could enter the Ironman.

Tri Harder, Chrissie Wellington's training programme is available from audiofuel.co.uk for £3.75.

Chrissie Wellington's top tips on how to find your motivation

• Set a goal Take an honest look at where you are now and plan how you're going to get from there to where you want to be. Not just in terms of the training, but rest and recovery, the equipment you might need to use, your nutrition. Focus on the gratification that will come from achieving something new. You'll feel so good, physically and mentally.

• Get support towards your goal It's hard to do it alone and sometimes you need to lean on people. It doesn't have to be a training buddy, it could be a friend or partner – someone to say: 'Go on, get out the door." Joining a club is fantastic. There are around 600 triathlon clubs and they provide this amazing cocoon of support, camaraderie, advice, coaching. Contrary to what you think, they're not just for athletes. You can go as a novice and find the support you need.

• Celebrate successes on the way You're going to have highs and lows, but if you enjoy the journey and celebrate successes you will feel you are achieving something.

• If the weather is putting you off, adapt your training Go for a swim instead of a run. Or get out there and endure it and see that as part of the challenge.

• Find inspiration Music is an inspirational tool, although don't use it when you are outdoors on a bike. It helps me to put on songs that remind me of good things, or lift my spirits, before I go out training. I also have a dog-eared copy of Rudyard Kipling's poem If – and I write lines from it on my water bottles when I race.