Pistorius, born without fibulas and who had his lower legs amputated when a baby, uses carbon fiber prosthetic running blades and is hoping to qualify for the 400 meters at the Games.

Pistorius beat the Olympic qualifying time of 45.30 in Pretoria in March but must repeat that performance in an international meeting before June 30 to make the team for the London Games which start on July 27.

Pistorius, who has a personal best is 45.07, won the 100, 200 and 400 gold medals at the 2008 Paralympic Games. He also became the first amputee to compete at the athletics world championships when he ran in Daegu, South Korea last year.

"The science is fully clear that ... Mr. Pistorius runs considerably faster with his artificial limbs," said Peter Weyand, associate professor of Applied Physiology and Biomechanics at Southern Methodist University in Dallas.

He said in an email that the findings, with Matthew Bundle, assistant professor at the University of Montana's Department of Health and Human Performance, also showed Pistorius had an advantage over one legged amputees.

Pistorius has already won a legal case to compete against able-bodied athletes after the Court of Arbitration for Sport in 2008 overturned a ban which had been imposed by the International Association of Athletics Federations (IAAF).

The court said its ruling applied only to Pistorius and only to the type of artificial limb he uses and that the IAAF had failed to prove its case.

The irony is that data used in support of Pistorius at the arbitration court came from a group which included Weyand and Bundle. They only made known their dissenting opinion later and five other scientists in the same group reject their arguments.

Icelandic company Ossur, which makes the carbon fiber limbs, and the athlete himself, are certain he has no advantage and that is it sheer hard work which is behind his success.

"I have been competing on the Ossur flex foot Cheetah since I first started in athletics in 2003," said Pistorius.

"The leg has not changed and I have not run on any other prosthetic sprinting leg. My advances in time are down to how hard I train," he added in an email.

The futuristic look of the limbs, which are curved like an upside-down hook and which affix via sockets to the stumps of his legs, have earned him the nickname "Blade Runner".

The science behind the limbs themselves is surprisingly simple and has barely changed since Pistorius first starting using them, according to Richard Hirons, a clinical prosthetist and specialist in sports feet at Ossur.

"The bottom line is that it minimizes the disadvantages," Hirons told Reuters. "He is basically on stilts, he has to take that into account, he has to think about the wind, he gets nervous when it rains.

"There is a big amount of extra effort required in the upper body to generate power, lift and compensation," he added.

CHEETAH INSPIRATION

Ossur, founded in 1971, makes many limbs and works with many Paralympians, but Pistorius is their highest profile client.

The limbs he uses, called the Flex Foot Cheetah, were developed by U.S. inventor Van Philips in the 1980s.

He had the bottom half of his left leg cut off by a motor boat when water skiing, but was a keen sportsman and was frustrated by the clunky prosthetic designs then available.

Ossur bought Philips' company in 2000 in an international expansion which has made it a leading global prosthetics firm, growing well beyond its Icelandic birthplace. Sales grew from $18 million in 1991 to $401 million in 2011.

Hirons said the limbs were curved carbon fiber, which were specially designed for high impact sports. The company also produces limbs with a more gentle curve for joggers, as well as feet and legs for daily use for ordinary people.

Also for non-athletes, the future is bionic limbs, combining small electronic motors and computer sensors.

Despite the findings of Weyand and Bundle, Ossur says the carbon fiber legs are much less efficient than real legs, ankles and muscles in absorbing the impact from running and returning energy back to the runner for forward movement.

"There is a huge amount of extra effort required in the upper body to generate power and lift and compensation," Hirons said of Pistorius.

SCHOLARLY DISPUTE

Weyand and Bundle disagree, setting out their views in a debate with their five fellow scientists who worked on the Pistorius case in an issue of the journal Applied Physiology in November 2009. They say the prosthetic limbs are lighter than legs and allow Pistorius to take quicker strides.

That meant he spent more time getting tread on the ground and less in the air, which in turn meant his athleticism needed to be less than able-bodied runners to reach the same speeds.

"We conclude that the moment in athletic history when engineered limbs outperform biological limbs has already passed," the two men wrote.

In a rebuttal, the other five scientists completely disagreed, writing that it was "common sense that amputation and prosthetic legs impair force generation".

They said the rapid leg swings could have resulted from training and Pistorius having to compensate for his disability.

Weyand told Reuters that he stuck to his views, which he said were backed up by scientific data.

While the scientists debate, Pistorius is still working to achieve his Olympic goal, though has fallen short so far.

"I have worked hard to achieve the Olympic qualification time - I have already run this time twice and my aim is to consistently run within this time ahead of the Olympics and I hope to be selected to represent South Africa," he told Reuters.

(Reporting by Patrick Lannin in Stockholm, Editing by Peter Rutherford)

• A Permanent Economic Emergency