The world record for covering 26 miles and 385 yards on foot is a shade over two hours. So giving yourself two months might seem a bit generous, says Mark MacKenzie. Unless, that is, you run it every day

When London staged its first public marathon in 1981, the concept of running 26 miles and 385 yards for fun was, it's fair to say, a relatively new one on these shores. The oldest mass-participation version of the Olympic event is the Boston marathon, founded in 1897. These days, a race of relative stature is held in a major city almost every weekend. And nowhere makes a more cogent argument for the marathon as the fitness phenomenon of modern times than North America.

The waistbands of a continent may be straining against the ceaseless spread of the Super Size culture, but there is a flip side to this increasing flop of gut and girth. Conservative estimates suggest the US is home to around 25 million recreational runners, a market worth billions of dollars to shoe and clothing manufacturers and one, in part, fuelled by the near-messianic zeal of the plethora of clubs and societies devoted to the marathon distance.

One of the more special-ist is the 50 States Mara-thon Club, whose member- ship is restricted to those who have pushed themselves the full marathon distance in each of the 50 American states. Until last weekend, the number of inductees ran, literally, to an impressive 1,186. But when runner No 50 crossed the finish line of Saturday's New York Marathon, that figure increased by one.

Perhaps what was most remarkable about the efforts of the 43-year-old Dean Karnazes was not merely that he had completed this Herculean feat but the time it had taken him to do so: 50 consecutive days. Just so we're clear, that's a marathon a day for the best part of two months.

Starting in the Missouri town of St Charles, Karnazes had zigzagged his way across the US towards the Big Apple. En route, he was joined by athletes from as far afield as India and Japan, many of whom had learned of his run from his website. Signing up in their droves to "run with Dean", they set about creating a Forrest Gump for the MySpace generation.

"The original idea was to do it by myself," explains Karnazes, "as a sort of vacation." At this point, it would be disingenuous not to point out that Dean Karnazes and distance running have a bit of history: the affable San Franciscan is one of the world's leading ultra-distance runners.

To the uninitiated, the world of the "ultra" is one in which marathons are broadly defined as anything in excess of 26 miles, 385 yards. At the sharp end of the sport the heavyweights, of which Karnazes is one, rarely get out of bed for anything less than 100 miles. The most gruelling race of all, the Badwater Marathon, is a 135-mile, not-so scenic tour of California's Death Valley at the height of summer. Then there are Karnazes's "non-stop" records, culminating, last year, in a 350-mile circuit of San Francisco's Bay Area.

What most would consider acts of mindless masochism, men like Karnazes interpret as testing the limits of the human machine. Around 15,000 Americans take part in ultras every year - and the numbers are rising.

Karnazes is a rare breed of athlete, a relative latecomer (he only took up running on his 30th birthday) but one genetically predisposed to the demands of ultra-distance. "My natural biomechanics [running gait and joint alignment] are good, so I don't suffer over-use injuries," he explains.

That a certain natural sel-ection differentiates wheat from chaff among endurance athletes is a theory supported by various scientific studies. Nevertheless, to help him prepare for the Endurance 50, Karnazes has, since last March, called on the services of Chris Car-michael, a top conditioning coach known primarily for his association with Lance Armstrong, the seven-times winner of the Tour de France cycle race.

"Chris had me do lots of fast work, the sort of thing I hate, such as interval training and hill repetitions," Karnazes says. Clearly, he is a man built not for speed but for discomfort.

It was Carmichael who honed Armstrong's running technique ahead of his marathon debut in New York last weekend. The former triathlete had told the press he hoped to get home in around 2hr 45min, but had to settle for 2hr 59min 36sec. "I thought he would have been faster," says Karnazes. "Had I known he was so close [Karnazes finished in 3hr 30sec] I would have sprinted to catch up."

In a nation dominated by American football, baseball and basketball, Karnazes says he has been pleasantly surprised by the interest shown by the US media. "In New York I tried to put my head down and run as hard as I could, but most of the time I was talking to people."

Indeed, one of the more disconcerting aspects of Karnazes's marathon sequence is its effect, or lack of, on his body. "The challenge was to try and finish each day in the best shape I could," he says. With Car-michael's input, Karnazes conditioned himself to run 26-odd miles in a maximum three-and-a-half hours - with almost no sign of fatigue. To prove the point, he has done so with a heart rate rarely exceeding 110 beats per minute, roughly the same level of exertion a moderately fit person might experience on a modest jog. Remarkably, not once in 50 days did he hit the dreaded "wall", the debilitating phenomenon that occurs when the body runs out of glycogen, inducing sudden and overwhelming exhaustion.

To help him avoid this, Karnazes consumed around 6,000 calories a day [the recommended intake is around 2,500], consisting mainly of carbohydrates, protein-rich salmon six nights a week, and what he describes as "finger food", vast quantities of low-fat cookies he ate while running.

Thereafter, the main challengewas one of logistics. "The distance between the runs made it difficult to establish a daily routine," he says. "In a state like New England, the next run was only an hour away, but in South Dakota, for example, as soon as I finished my run we had to drive for 12 hours to the next one.

"Last Sunday was the first day in 50 that I hadn't run a marathon, and to be honest, it didn't feel very good," he says. "The endorphins the brain generates through running create an emotional high, a very positive feeling that's very addictive. The afternoon following New York I started to get a little stiff."

The solution? "I went out and ran a marathon that evening." And as you read this, Dean Karnazes is several days into his next endurance project, running back home to San Francisco: all 3,100 miles.



For more details about Dean Karnazes's 50 marathons in 50 days: To learn more about the 50 States Marathon Club, including qualifying rules:

Dean Karnazes talked to Mark MacKenzie courtesy of The North Face; to view their full range of products: