Paula Radcliffe had the pedigree, the past performances and a track tailor-made to showcase what she does better than any woman in the world: run for kilometres with metronome-like precision.

So no one should have been surprised when the 28-year-old British runner was the first woman across the finish line of the Chicago Marathon on Sunday, or that she covered the 42.195-kilometre course in a world record of 2 hours 17 minutes 18 seconds, lopping nearly a minute and a half off the old mark.

Even less surprising, though, was what Radcliffe did afterward. She insisted on taking a drug test.

"I just wanted to make sure that was done," said Radcliffe, the two-time world cross-country and half-marathon champion, "so there could be no questions and no issues about this one."

That reveals as much about her sport as Radcliffe's place in it.

No one who competes in track and field is above suspicion of using performance-enhancing drugs. The same with cycling and all the other endurance sports -- and for that matter, baseball, football, soccer, hockey, golf and even chess.

What makes Radcliffe stand out, beyond her success the past two seasons, is that she welcomes the scrutiny, even insisting on it.

Remember how baseball slugger Sammy Sosa chafed at the offer of a surprise test to back his claims about being steroid-free?

Well, Radcliffe refuses to let any opportunity slip away without doing just that.

While climbing steadily toward the top, Radcliffe has raised the stakes in her crusade against erythropoietin, a performance-enhancing drug known simply as EPO.

She wears a red ribbon on her singlet to show support for compulsory blood testing, a more effective method than urine tests, and she's authorized release of her own blood tests from just about every race she's run in.

At the world championships in Edmonton last year, Radcliffe sat in the stands during the heats for the 5,000 metres holding up a hand-lettered sign. It read "EPO cheats out," and it was intended for Olga Yegorova of Russia, who had tested positive for EPO but was allowed to compete on a technicality.

David Moorcroft, an outstanding distance runner who was the head of the British federation at the time, warned Radcliffe she'd "spend the rest of her life looking over her shoulder," wondering whether someone had spiked a postrace drink, a snack or even her toothpaste.

Radcliffe explained in an interview later why she thought that isn't too steep a price to pay.

"Too many people think we're all at it," she said. "It's like the Tour de France. Because no cyclists stood out against the cheats, they all got tarred with the same brush -- those who wouldn't touch a drug condemned along with those who are full of the stuff.

"And I don't want that to happen in my sport."

Like Lance Armstrong, she knew what to expect after setting herself up as a beacon for drug-free performance in a sport shrouded with illicit substances.

She's been asked to prove her innocence over and over, and so far, Radcliffe has produced the goods.

What has changed, however, is the size of the stage she commands.

Radcliffe was practically born to run. Her great aunt won an Olympic silver medal as a swimmer for Britain in 1920 and her father was a respectable amateur marathoner in his spare time.

When she was 11, her father moved the family to Bedford in the English Midlands and she found in the fields surrounding the town that running could be both her love and her livelihood.

A string of disappointments steeled Radcliffe for the tough times ahead.

Before her breakthrough 2001 season, her principal weakness at distances from 3,000 metres through 10,000 metres was the lack of a finishing kick.

But the consistency that enabled her to stay with the elite competitors in so many of those races, producing lap after lap at nearly top speed, has been her greatest asset in both of her remarkable marathon performances.

In Chicago, with the temperature just above the freezing point and a stiff wind facing the runners heading home, Radcliffe methodically ground down the competition.

She ran the second half of the course a minute faster than she did the first, leaving her final threat, two-time defending champion Catherine Ndereba of Kenya, sputtering in the 27th kilometre.

The only time Radcliffe stopped after that was to leave a sample for drug testing.