Heee-haaww. Heee-haaww. I am 16 minutes into a gentle jog with Paula Radcliffe. My breathing sounds like an asthmatic donkey down a coalmine. Radcliffe is gliding across thick mud as if she were walking on water. I glance at her and then feel better. Nod, nod, nod: Radcliffe's inimitable running style, her head bobbing rhythmically above tucked in shoulders, has finally kicked in. It's a nod of delicious self-absorption; her legs and lungs working together; her body ticking like a metronome.
My friends say I run like a girl. If only. You don't need a session with probably the greatest female distance runner ever, who still holds the women's world record for the marathon, to know that girls can run pretty well.
Before we start, Radcliffe looks fragile in the goose-pimply flesh, freezing in the bitter wind sweeping across Regent's Park in central London. As soon as she unfurls her limbs to warm up with some basic stretches, however, she shows all the elegance of those unusual people who somehow come alive when they are in motion.
By interviewing Radcliffe on the run, I cunningly hope that short questions, which demand long answers, will help me keep up. Failing that, friends cruelly suggest, I could always take a roadside toilet break, as Radcliffe famously did in the 2005 London Marathon.
Radcliffe began running after trotting along to her amateur runner dad's marathon training sessions and handing him drinks. She finished second in her first cross-country race at school, which fired her competitive spirit. "I was really annoyed because this girl beat me - I was only about eight or nine - so my dad took me to a little circuit every Saturday for four weeks and taught me how to run downhill and just relax more and let my body go. On the next race I got away from her on the downhill."
Running is more like an addiction than a job, Radcliffe cheerfully admits while we swerve past the duckpond. She does not feel she has to run every day - just seven days out of eight. And after a marathon, she takes two weeks off. "The first week I'm all right, I'm having a lie-in in the morning, doing different things and recovering from the race." By the second week, she's · getting twitchy. "You suddenly realise that running is your stress release," she says. "In the second week I'm dying to go for a run."
I assumed that Radcliffe would prefer running alone but she says that she can enjoy it both as a solitary therapy or a social occasion. "There are times when I'm feeling a bit down or have a lot of things on my mind or have had a really full-on, busy day, and I just want to go and have my time. And there are other times when it's a big social thing - go for a run, catch up with friends and have a really good chat."
She looks as if she has recovered from the disappointment of the Beijing Olympics, where she hobbled in at 23rd place after struggling with injuries all year. Last month she won the New York Marathon and is now firmly in training for next year's London Marathon, where she set her world record in 2003. Running with me is officially a rest day; most of her training is on the coast road near her home in Monaco. "I love running by the sea," she says. Her husband and coach, Gary Lough, still unfortunately remembered for berating a tearful Radcliffe for failing to do better in a 2001 race, used to run alongside her but now cycles to keep up. "He'll sing or do silly stuff - if I'm running quite hard so I'm not really talking he'll do a lot of things to take my mind off it."
In January 2007, Radcliffe gave birth to her daughter, Isla, after continuing to run "the whole way through" her pregnancy.
She found that childbirth toughened her up. "I came back physically stronger, with more endurance but also mentally stronger," she says, gracefully navigating around a small swamp, which I plough straight into.
Never mind her serious tips, what does all this pounding the streets do for her toenails? "I have them painted so you can't see how bad they are," she laughs. Actually, although she lost a few toenails after her first London Marathon in 2002 because her feet slid forwards in her shoes, her feet are fine now: her trainers are custom-made to her exact size - 6.75.
She has always been known for embracing innovation, from ice baths to emu oil. This year, she reveals she has been wearing a mouthguard on her lower jaw to correct imbalances in her lower spine. Will it stop the famous nodding? "No, that's part of my running style," she says, and something she has learned to draw strength from.
Radcliffe starts to pick up the pace. She doesn't get frustrated, she says, by people going on about her Olympic disappointments - four Olympics and no medals. She "definitely" thinks "it's possible" she could run in 2012. She will be 38 then - the same age as Constantina Tomescu, the Romanian who won the women's marathon in Beijing this year. Radcliffe says she is as motivated as she was aged 21. "The main thing now is to get the period of training I need without getting injured."
Charitably, she only subjects me to full marathon speed for the final 200 yards. This is my sprinting speed; she can keep this up for 26 miles and 385 yards. At the end, when I take my hands from my knees, she tells me how a small child recently asked her why she kept coming back after being disappointed. "You know, I actually do enjoy it."
She doesn't really need to say so. In motion, everything seems to click for her. "OK, it's disappointing and high-pressure in some situations but I'm lucky. My job is what I do for fun as well," she says. "When I come through a disappointment my natural instinct to feel better is to go for a run. And then I'm also getting ready for the next race".
Paula Radcliffe's distance running tips
• You don't need to run every day. Take proper time off after a marathon to allow your body to recover. Radcliffe takes two weeks.
• The building blocks of Radcliffe's basic training are short runs - either five 2km runs or six runs of a mile. Then she adds in a long run, which she progressively extends throughout her training.
• If you suffer from stiff calves (as I do), wear knee-high compression socks.
• Training can be mentally harder than the actual race. When you hit a wall in a marathon, recall these "rough spots" from training as evidence you can get through it.
• If you are struggling, use disassociation techniques to take your mind off the pain. Slowly count to 100 three times, which covers a mile (for Radcliffe).
By the time she has finished, she usually feels fine again.
· Paula Radcliffe is promoting the Nike+ training system, whereby a chip placed in your running shoe transmits time, distance, speed and calories burned to your mp3 player. www.nikeplus.com