This time last year, Carole Nicoll felt “slugged by stress”. To shake it off, she needed to do something extreme. “I was watching the London marathon on TV and decided - that’s it. That’s a radical thing to do. After all, human beings just aren’t meant to run 26.2 miles.”

Whether they’re meant to or not, plenty do. This Sunday morning, more than 30,000 competitors will line up in Greenwich for the start of the 22nd Flora London marathon - with teachers likely to make up the largest professional group. Carole - a primary teacher at Robert Gordons College in Aberdeen - will be among them. So, too, will Bruce Watson, a French teacher from Walmer school, near Dover. He entered this year’s event to follow colleagues who’d run in previous years. “They laid down the gauntlet - and I’m not one to resist a challenge.”

Bruce and Carole are certain about one thing. There may be dozens of marathons, but for them, only London will do. “Other marathons don’t mean anything,” says Carole, who faces a 1,000-mile round-trip. Because most people feel the same way, the event is several times oversubscribed.

Carole knows she’s lucky to be accepted at the first attempt and is determined to make the most of it. For the past few months she’s been out running by 6.30am each day. Her husband and four children are only just surfacing by the time she gets back. She says her whole day is shaped by this first hour-and-a-half. “It’s changed my life. If I’ve had my morning run, I can handle anything the day throws at me.”

But Bruce has yet to notice any life-changing benefits. “I haven’t even lost weight,” he says. “If I go for a run and burn up calories, I just treat myself and eat more. The only way my life has changed is that I’ve given up beer until after the race.”

But then Bruce hasn’t been taking his training quite as seriously as Carole. Her preparation has been carried out in accordance with the schedule laid down in Runner’s World magazine: a carefully balanced programme of speed and endurance training. Bruce, meanwhile, has been going for “a big run every weekend”. He says:“Yes, I know you’re supposed to follow a schedule, but I don’t really have time. Every week, the head of PE puts a training programme in my pigeonhole. He’s just trying to make me feel bad.”

Bruce’s preparation has centred on some “last-minute cramming”, courtesy of this year’s marathon falling at the end of the Easter holidays. A few weeks ago, the furthest he’d run was a half-marathon - which he completed with mixed emotions. “I ran it in 1hr 49min, which was pleasing. But to think that was only halfway? Very scary.”

Carole, meanwhile, hit her training peak back in February with two 20-mile runs in a week. “I wasn’t out of breath,” she says proudly. “I was in pain, but I wasn’t out of breath.” She has stuck strictly to her schedule, running every day - around town when the weather has been fine, or down on the beach to escape the winter snow.

Pounding the streets, clocking up the distance, going the extra mile. It’s not everyone’s idea of fun - even Carole had doubts at first. “It’s boring - very boring.” She tried listening to music on her Walkman, or training with a friend so they could talk. But then she discovered that boredom has its advantages. “After a few miles you go into a trance. Your mind clears of all its clutter, and you get these tremendous thoughts from nowhere. It’s a kind of meditation.”

This spiritual dimension seems to have eluded Bruce. “Enjoy it? No way. I’m only doing this so that I can say I’ve done it.”

Of course, it’s one thing to achieve a trance-like reverie running along a deserted Aberdeenshire beach with only a few seals for company, quite another to attempt it in the middle of a 30,000-strong field with 20 times that many cheering spectators lining the route.

Former London marathon regular and World Cup champion Richard Nerurkar warns that coming to terms with the crowd can be difficult for first-timers. His advice to Bruce and Carole is to have a plan and stick to it. “Just focus on running at your usual pace - don’t get carried away by all the cheering and clapping. Equally, if you get boxed in and it slows you down, don’t panic. The key is to conserve some energy for the last six miles - that’s when you’ll feel the pain.”

Bruce’s race plan involves following “a female runner with a nice behind”. It won’t be Carole. Not that there’s anything wrong with her physique - it’s just that Bruce probably couldn’t keep pace.

Carole tells friends she’s aiming for the four-hour mark, but when pushed admits her schedule is geared up for three-and-a-half. Bruce says he’ll be happy with four-and-a-half hours - but then reels off the exact times friends have run in previous marathons, and says he’d love to put one over on them. He also admits to a fear of being overtaken by an Elvis or a pantomime horse. “You don’t want too many in fancy dress going past you. You’ve got to keep your dignity.”

But they’re both confident they’ll finish. Richard Nerurkar points out that marathon runners compete against the clock and against their fellow athletes, but most of all, they compete against the distance. “That’s the attraction of marathon running,” he says. “Everyone who finishes is a winner.”

And if you’ve got the determination and you’ve done your training, what can stop you? The answer, most commonly, is injury or dehydration. The combined field of runners will shed 120,000 litres of sweat - enough to fill an Olympic-sized swimming pool - so keeping up your fluid intake is vital. It’s said that the biggest cause of failure in the London marathon is dehydration, and the second biggest is injury caused by tripping over discarded water bottles.

Barring such misfortunes, Carole and Bruce will experience the thrill of running up the Mall to the finish. But for Carole, the end of the race will mark the start of a new adventure. She plans to take up competitive long-distance running and, at 46, will be a youngster in the “super veteran” category. “I’ve come to the sport late, but I’m going to give it everything.”

Thirty-four-year-old Bruce, on the other hand, insists that once he crosses the finish line his marathon-running days will be over and life will be back to normal. The course winds its way past 76 pubs, and every one of them will remind him that he’s getting closer to his first pint in four long months.

“Oh yes, I’m looking forward to that,” he sighs. “Over those final six miles the thought of a nice cold beer will be my inspiration.”

‘Marathon Running’ by Richard Nerurkar is published by Aamp;C Black (pound;12.99). Details of next year’s race: tel 020 7620 4117 or visit the website www.london-marathon.co.uk. Entries accepted from August.

Roads to glory

If you want to run next year’s London marathon, you need to plan ahead. Entry applications are taken from August, and you’ll know by October if you’ve been lucky in the ballot. Some entrants have spent three or four years trying to secure a place - although you may be able to short-cut the system if you’re running for charity, or are a member of an athletics club.

Arran Peck of London-based personal fitness company The Tonic trains dozens of people each year who want help preparing for their first marathon. His tips for success include:

* If you can’t walk a marathon, you won’t be able to run one. Start off by walking 26 miles - that will give you a sense of what you’re up against.

* Be realistic when you set your targets. Don’t expect to run your first marathon in three hours; for most people that just isn’t going to happen.

* You’re going to be covering plenty of miles, so get some decent footwear. Poorly fitting trainers are a common cause of injury.

* Everyone’s training needs are unique. If you’re following a schedule make sure it takes into account your injury history and your starting level of fitness.

* Running a marathon is “a big ask” emotionally as well as physically. Joining a running club means you’ll always have people you can talk to.

* Marathons can easily take over your life - stay relaxed and keep a sense of perspective.

Website: www.the-tonic.com ‘After a few miles you go into a trance. Your mind clears of all its clutter, and you get these tremendous thoughts from nowhere. It’s a kind of meditation’