The idea of a bionic superman - part machine, part flesh and blood - used to be science fiction.

Now, it's a reality that keeps knocking stubbornly at the door of the sports world.

"We can produce athletes who can produce world records," said Benno Nigg, professor and director of the human performance lab at the University of Calgary. "But does the sports world want them?"

He is not talking of steroid-enhanced musclemen but of athletes who use high-tech prostheses to replace the actions of limbs missing because of amputations or birth defects. Technically they're referred to as athletes with disabilities, but what has been considered a physical limitation in the past is now being cast as a mechanical advantage.

A report published last week by human performance researchers Peter Weyand of Southern Methodist University and Matthew Bundle of the University of Wyoming in the Journal of Applied Physiology said double amputee sprinter Oscar Pistorius of South Africa enjoys an advantage over able-bodied competitors. In his 400-metre specialty, the self-described "fastest man on no legs" may be 10 seconds faster over the 400 on prostheses than he would be on two natural legs, the researchers say.

The Blade Runner - Pistorius runs with J-shaped carbon-fibre prostheses below his knees - has a faster stride rate and isn't subject to tiring of calf muscles and ankles. "The blades enhance sprint running speeds by 15 to 30 per cent," Weyand said in a statement.

Pistorius, 23, was born without the fibula bones in his lower legs, which were amputated when he was 11 months old. He has lived a sporting lifestyle nonetheless, and took up running as rehabilitation after a 2004 rugby injury. Ultimately, he became a Paralympic gold medalist, an amputee world record holder with visions of competing on South Africa's Olympic relay team.

In 2008, the Court of Arbitration for Sport overturned a track and field ruling that said Pistorius's prosthetic limbs gave him an advantage as a runner. The ruling had prevented him from entering races with able-bodied athletes. Pistorius was allowed to try to qualify for the Olympics by racing against able-bodied runners. He ran the 400 metres in 46.25 seconds, narrowly missing the Olympic qualifying standard.

The CAS had said its ruling did not open the door for all athletes with disabilities to compete in the Olympics, but allowing Pistorius to line up as an equal alongside able-bodied athletes was heralded in many quarters as a victory for athletes with disabilities. His lawyer, Jeff Kessler, called it a step toward equality.

But the opinion that athletes with prostheses have an unfair advantage rekindles the discussion about whether athletes with disabilities belong in the same competition as able-bodied athletes.

"I don't think it's a good idea to combine the two," said Les Gramantik, the former Canadian national coach for track and field, who has worked with both able-bodied and mechanically assisted athletes with disabilities. It's too hard to determine how much of a performance is the product of human effort and how much is due to mechanics, he said.

"The prostheses are so good, so well designed now ... you don't want to have a war with robots," Gramantik said in an interview.

Nigg said researchers in the human performance lab used to engage in a little dark humour when they heard bizarre news stories of a sneaker-clad foot being washed up on the shores of British Columbia.

"We said they were all athletes who wanted prostheses to make then run faster," Nigg said. "With technology, I can make a high jumper or a shot putter. ... [For] almost all the disciplines in athletics, we could make the athlete."

Nigg has studied Pistorius's run against able-bodied athletes at a 400-metre race in Rome in 2007. Pistorius started slowly, not a surprise since the springy prostheses don't make for an explosive start, and had an adequate 100 metres around the first curve. But the South African sprinter got faster over the next 200 metres, including the next curve, and was reeling in other runners as he came home, finishing second.

"He does not have calf muscles that get tired," Nigg said. "He's an average athlete. But if he doesn't get tired, that's as good as the others. My gut feeling is that he has an advantage. ... But I cannot give you the proof for it."

Greg Wells, assistant professor at the University of Toronto specializing in exercise physiology, said several factors may be benefiting Pistorius's performance. He said Pistorius's speed - calculated as a number of metres travelled in a second - is within 2 per cent of what other runners achieve. But the cost to his body is significantly less. As a race gets longer, a fast start becomes less of a factor in the outcome while resistance to fatigue becomes a greater factor.

"We also see 20-per-cent less ground reaction force - the way the ground hits you back when you run. The impact on his body is less. And because the prosthetics are so compliant [springy], the recovery of his body is 16-per-cent faster than the able-bodied athlete. That makes for a faster stride rate," Wells said.

"It may be confusing for sport, but the technologies that are being developed in sport will get to the general public, and it will definitely help the differently-abled.

"It's cool that, for the first time, we can say Paralympians can exceed the performance of able-bodied athletes. It will change the way we perceive disabled athletes," Wells said.

Anna Parisi, spokesperson for the Canadian Paralympic Committee, said there are "a number of athletes with a disability from around the world pursuing the opportunity to qualify for the Olympic Games, and we are supportive of that."

But athletes with disabilities won't be taking over those Games. "We're not in competition with the Olympics," she said.

Manufacturing performance

Ossur, the company that manufactures the Flex-Foot Cheetah prosthetic limbs worn by South African sprinter Oscar Pistorius, was quick to react to the Weyand-Bundle report published in the Journal of Applied Physiology, accusing the researchers of limiting their view to the product and not the whole runner in suggesting amputee athletes are getting an advantage over the able-bodied by running with prostheses.

"More than 30 years of experience in the research and testing of prosthetic limb technology have taught us that the prosthesis is what makes amputees whole and able to engage in activities such as walking and running. Amputees also view themselves as whole-bodied when wearing their prosthesis. To test a prosthesis separately as a component, and not as an integrated part of the amputee's body, generates data that is technically incomplete and flawed.

"Engineers [Peter] Weyand and [Matthew] Bundle have elected to see the amputee and the prosthesis as two separate biomechanical objects. This counterargument denigrates our efforts and has a discouraging effect on scientific development," the statement said.

The technology used in making the leg has been around for 12 years, the Iceland-based company said, adamantly defending Pistorius, who has broken amputee world records 27 times. He is not taking unfair advantage or using a recently invented technology.

The company called it "unfortunate and regrettable" that the achievements of athletes wearing artificial limbs "are repeatedly discredited and that precious time that could be devoted to training must be - again - devoted to explicating themselves and addressing public perception," the Ossur statement said.