The athlete Oscar Pistorius made history in July when he became the first amputee sprinter to run alongside able-bodied athletes at the Olympic Games, competing in the 400 m in both the individual and relay events in London. Continuing his busy summer schedule, the South African sprinter is now at the Paralympic Games, also in the UK capital, where he is the defending champion in the 100 m, 200 m and 400 m for his class. Nicknamed the "blade runner" because of the iconic artificial limbs on which he runs, Pistorius has fast become one of the world's biggest sports stars and he is redefining what it means to be "disabled".

One of the most poignant moments of the London Olympics followed the second semi-final of the men's 400 m. After winning the race, Kirani James of Grenada, who would eventually win gold in this event, immediately turned round to seek Pistorius, whom he embraced and made a point of exchanging name bibs with in a gesture of respect. It was a powerful symbol that showed how Pistorius is fully accepted among his fellow competitors. Pistorius finished eighth in the race and so did not qualify for the final, but he told journalists shortly afterwards "I am struggling to find a way to describe it. It is really humbling all the support I have had". However, the journey to becoming this celebrated Olympian has not always been an easy one for the 25 year old from Pretoria.

Pistorius has not always enjoyed such widespread support. In 2007 his ambition to compete alongside able-bodied athletes faced a major setback when he was banned from competing in all able-bodied athletics competitions by the International Association of Athletics Federations (IAAF). The move came after Pistorius had been invited to take part in a series of scientific tests at Cologne Sports University in Germany under the guidance of one of the university's academics along with a member of the IAAF. Questions about his performance were raised when Pistorius had started to run sprint events in times comparable to able-bodied athletes. The report, following two days of testing, concluded that when Pistorius is running at the same speeds as able-bodied athletes, he is using less energy. These findings led to an IAAF vote and the subsequent ban. But why did the IAAF take issue with Pistorius? It was surprising given that the history of athletes competing with the aid of varying forms of prostheses dates back to before the original Olympic Games in 776 BC. What was different about this case?

The Cheetah Flex-Foot

Pistorius, who was born without lower leg bones, underwent a double amputation aged just 11 months following the advice of medical professionals who said an early operation would greatly increase his prospects of mobility later in life. Having developed an interest in sport as a child, Pistorius focused on track running at the age of 17, competing in his first track session at the beginning of 2004. It was later in that same year that Pistorius first began using a J-shaped prosthesis known as the Cheetah Flex-Foot. Pioneered by the US bioengineer Van Phillips and now produced by the Icelandic company Össur, the design of this prosthesis has been optimized for sport. This is in contrast to the more typical designs for which day-to-day walking as well as a natural-looking appearance are the top priorities.

Crafted out of carbon fibre, the Flex Foot prostheses are strong and light but also utilize the fact that carbon fibre is anisotropic, meaning that its response varies depending on the direction in which a force is applied to it. The prosthesis is produced so that the grains of carbon fibre are aligned parallel to the curve of the J. The outcome is that the upper part of the J, which attaches below the knee, is desirably rigid because the downward force is parallel to the grain. But at the bottom of the J where the leg makes contact with the ground, the prosthesis flexes, storing energy that is then released back through the limb and into the athlete's body as they push off for their next stride.

It is this "spring in the step" that led the Cologne study to conclude that Pistorius was able to run with his prosthetic blades at the same speed as able-bodied sprinters with roughly 25% less energy expenditure. The sports engineer David James, who was not involved in the Cologne study, says that, in biomechanical terms, running can be thought of as a series of jumps. "It costs you energy to rebound and to bounce," he says. "It has led to this interesting question about using this prosthesis because it stores spring energy and returns energy, unlike muscle and bone. Perhaps using these prostheses creates an advantage for the athlete." James, who is based at the Centre for Sports Engineering Research at Sheffield Hallam University in the UK, discusses the issues surrounding Oscar Pistorius's running style in this video interview with Physics World.

Pistorius fights back

But Pistorius – who was by now used to facing relentless questions – was not going to take this ruling lying down. Along with his support team, Pistorius has always maintained that the reasons he is able to compete with able-bodied athletes are natural ability and hard work alone. They point out that the Flex Foot prosthesis has been used by Paralympic athletes since 1996 and that Pistorius has been competing with the same pair of blades since 2004, during which time he has achieved a marked improvement. In fact, the prosthesis used by Pistorius is relatively old and "low tech" compared with some of the newer sports prostheses available today.

Pistorius challenged the ban via an appeal and travelled to the US to take part in an alternative series of testing at Rice University in Texas. While the Cologne tests focused only on the biomechanics of Pistorius running at full speed in a straight line, this second study also investigated the elements of track running where Pistorius may face a disadvantage, such as at the start, where athletes need to rapidly accelerate. The results from the Rice tests were analysed by a team of researchers in biomechanics and physiology from six universities led by Hugh Herr of the Massachusetts Institute of Technology. The group's findings challenged the conclusion of the Cologne study that Pistorius has an unfair advantage in the 400-m race.

Pistorius took his case to the Court of Arbitration for Sport in Lausanne, Switzerland, which was addressed by Herr along with one of his scientific colleagues. In May 2008 a panel unanimously determined that the scientific evidence did not support the claim that Oscar Pistorius has a net advantage over able-bodied athletes. The ban was revoked with immediate effect. "While an athlete's performance in sprints of very short duration is determined almost entirely by mechanical factors, in races of longer duration, such as the 400 m, performance depends on both mechanical and metabolic factors," said Herr. In other words, the science is much more complicated than the Cologne study suggested and the basis for the ban was flawed.

Possibly because of the disruption to his training regime caused by the ban and subsequent appeal, Pistorius did not achieve the qualifying times required to be part of the South African team that took part in the 2008 Olympic Games in Beijing. He did compete, however, in that summer's Paralympics and became the first athlete to win gold in the 100 m, 200 m and 400 m events in the T43/T44 disability sport classification. Over the past four years Pistorius has raced alongside able-bodied athletes and his improved performances enabled him to be included in the South African team for the 2011 IAAF World Championships in Athletics held in Daegu, South Korea. Then came the Olympics this year where he was selected to compete in the South African 4 × 400 m relay team, which opened up the possibility of competing in the individual event despite having narrowly missed out on the South African team's qualification requirements.

The scientific debate keeps running

While Pistorius's career goes from strength to strength, the scientific debate about the use of running-specific prostheses has not disappeared entirely. Of particular note, two of the scientists involved in the analysis of the Rice tests, Peter Weyand of the Southern Methodist University in Texas and Matthew Bundle of the University of Montana, have since claimed that prostheses may indeed provide advantages. In a paper published in the November 2009 issue of Journal of Applied Physiology the pair suggests that other mechanical factors, including unusually fast leg swings caused by their light weight, can take prosthetic legs beyond the limits imposed by human biology. "The moment in athletic history when engineered limbs outperform biological limbs has already passed," they concluded in this paper. A more recent study by researchers in the UK and Malaysia, published earlier this year in Journal of Sports Engineering and Technology, also appears to support this conclusion. These researchers looked in particular at the manner in which sports prostheses can store energy during the early stages of running events, which can then be released to assist the athlete during the latter stages when they are battling with fatigue.

The extent to which this meandering scientific debate affects Pistorius is unclear, but in interviews he appears to be tightly focused on his sporting ambitions and challenges. When asked about his legs, Pistorius regularly quotes his sporting motto "You're not disabled by the disabilities you have, you are able by the abilities you have". Seemingly, it is this drive and focus that has enabled Pistorius to achieve so much in such a short space of time. His status as an athlete and cultural icon will undoubtedly be further boosted by his appearance at the Paralympics – an event whose stature is growing exponentially. Whatever happens next in the scientific debate, Pistorius is above all else an elite athlete who is raising profound questions about the use of the term "disabled". He is helping to transform attitudes and mindsets.

The July issue of Physics World also contains a feature about sports prostheses, exploring prostheses for cycling and the latest technologies that will feed into future prosthetic designs. For a limited period you can download a free copy of this special issue on the physics of sport. You might also want to watch these videos on the biomechanics of running, cycling and swimming.