Lance Armstrong won the Tour de France for a record seventh time this weekend, a stunning culmination to what has been a storybook racing career.

Most of us cannot imagine cycling for three hours, let alone the three weeks of constant riding the competitors in the Tour de France do. This year, it spans 3,600 kilometres -- about the drive from Calgary to Montreal -- with cyclists riding about 160 kilometres a day across the Alps and Pyrenees.

It is so demanding that more than 25 riders have dropped out this year.

You'd think you'd have to be superhuman to complete the race. But then again, Armstrong just might be: His body is so uniquely efficient, he is literally one in a million.

Physiologist Edward Coyle, who runs the Human Performance Lab at the University of Texas in Austin, has studied Armstrong's body for eight years. He's discovered that the cyclist has an oversized heart that has grown through training to become 30 per cent larger than the average man's.

His heart can pump nine gallons of blood per minute, compared to five for the average person. In fact, Coyle estimates that the 5-foot-10 Armstrong had a heart proportional to the size of a 6'6 man.

Armstrong's lungs can absorb twice as much oxygen. His muscles produce half as much lactic acid and expel it faster, allowing him to ride harder up the Tour's notoriously brutal hills and then recover quickly.

An average person turns 20 per cent of the oxygen he breathes into muscle power. Armstrong gets 23 per cent -- close to the highest ever recorded in a human. So with each breath he delivers more power to each push of the pedal.

Armstrong's body is so unique, if he didn't train at all, he would still be in better physical condition than an average person in top condition.

But of course, it's not fair to attribute Armstrong's Tour victories solely to his incredible body. Let us remember that before he was diagnosed with cancer nine years ago, the 33-year-old Armstrong had never won the Tour, even though he had the same genetic gifts.

Coyle says what really makes Armstrong unique is his determination and discipline.

''There are about 1,000 people in the U.S. between the ages of 15 and 20 with the same physiological potential as Lance, but none of them will achieve what he has without the training and the daring of Lance,'' Coyle told the Miami Herald.

In fact, it was likely precisely because of his bout with cancer that Armstrong has become the focused athlete he is today. In 1996, Armstrong was diagnosed with an advanced stage of testicular cancer that spread to his lungs and brain. He faced a 60 per cent mortality rate. And he beat it.

"It was the grueling experience of the treatment that convinced him how resilient his body was," Coyle told the Herald. "He lost weight and he got the confidence that he could race better at a lower weight.''

That confidence has helped Armstrong forge a deep discipline to his sport, says Dave Brailsford, the performance director at British Cycling.

"He pays attention to every last detail that contributes to the pursuit of excellence. That's what sets him apart," Brailsford told The Observer newspaper.

"He is always looking to make a tiny improvement to his nutrition, his position on the bike, or the science of how he trains."

Armstrong has a disciplined diet that has him weighing each meal to ensure he does not go above his optimum weight. At the start of the Tour, his body-fat ratio was a stunning five per cent; the average man has between 15-17 per cent fat.

He also focuses his workouts over the year on one race: the Tour. Many of his competitors gear up for several races a year, risking over-training and pushing their bodies to their limits too often.

The veteran cyclist reportedly doesn't even shave his legs before racing, fearing that the minimal energy required to regrow the hair might slow him down a fraction.

Armstrong's personal trainer Chris Carmichael tells ABC News he's convinced it's Armstrong's determination and energy that set him apart.

"I've worked with great athletes from all different sports. There is nobody out there like Lance Armstrong so far as having this incredible killer attitude."