Refining the prostheses and sport-specific wheelchairs that help Paralympic athletes compete is about removing barriers, rather than seeking an advantage. Stephen Harris looks at the latest developments and some of the controversies over where the technologies might be going.
When British sprinter Jonnie Peacock beat the South African Oscar Pistorius in the 100m at this year’s Paralympics, the sight of competitors racing on prosthetic running blades had long stopped being a novelty for most of the audience. The development of these carbon-fibre legs and other sports technology has played a big role in elevating the popular perception of the Paralympics so that, following London’s hosting of the most successful Games ever, they’re now regarded as a similarly elite competition to the Olympics themselves.
The basic technology behind many of these devices hasn’t actually changed much in the past 10 years. As a result, engineers are now looking for new ways to improve prostheses and wheelchairs within the strict rules of the Paralympics, with the focus falling increasingly on more personalised devices. And London 2012 offered a glimpse of some of these efforts to optimise the technology for disability sport’s new premier status and its latest superstar athletes.
The fast-paced and sometimes vicious sport of wheelchair basketball requires some pretty sturdy equipment. The players’ wheelchairs have to be able to withstand powerful collisions and stay upright as the players reach out to pass and shoot. Sadly, the Paralympics GB team narrowly missed out on a medal in London, but they did have the privilege of being the first British players to try out chairs that were custom designed and personalised for the athletes.
‘It’s been specifically designed for basketball and the Paralympics,’ said Mike Sheen, design and engineering manager of wheelchair manufacturer RGK. ‘Before we’ve had a design and constantly adapted it over 10 years, whereas now we started from scratch. We went back to the drawing board and we did the correct design process; we went back to CAD; we did a lot of stress analysis. We prototyped it and spent a year with someone in the chair getting it right, tweaking it.’
Funded by UK Sport as part of a £700,000 Paralympics research programme, the new chairs were developed by Loughborough University, BMW and RGK as a way improving the athletes’ speed and manoeuvrability while maintaining stability. By building each chair’s frame from aerospace-grade aluminium — which is better at absorbing collisions than titanium — the team was able to shave around 2kg off its weight compared with the previous model.
The chairs were also given personalised seats based on 3D scans of each player’s biomechanical movements and bean-bag-style moulds of their lower bodies and then constructed with hand-made cushions produced to fit them exactly. ‘The chairs vary massively in size depending on the user’s disability,’ said Sheen. ‘So someone who was a left-leg amputee would have all the upper-body strength and balance, whereas spinal injury needs lot more support and would typically sit a lot lower. When a chair fits and a chair works for somebody, it makes such a big difference that an able-bodied person wouldn’t understand.’
Custom designing — for both the sport and the athlete — is one of the key characteristics of the latest generation of disability sport technology and reflects the maturity of the Paralympic movement. As well as accessing the latest materials and designs, Paralympians can now make use of equipment that has been tailored for their bodies and abilities and the specific requirements of their sport. It was with this in mind that BAE Systems also became involved in the UK Sport wheelchair programme, applying a thorough requirement-capture process typically used for personal equipment such as fighter pilots’ helmets to determine the exact needs of each athlete.
‘This involved us having extensive interviews with the athletes,’ said Kelvin Davies, project manager for BAE’s technology partnership with UK Sport, which has seen the defence company donating £1.5m of engineering services. ‘They told us things we wouldn’t have found out any other way, particularly about the way they interfaced with chairs. A big revolution in that chair is the moulded seat and I’d like to think our capture contributed to the decision to go down that route.’
BAE also provided UK Sport with access to its wind tunnel — a first for British Paralympic sport despite the well-reported use that the Team GB cycling squad has made use of such facilities. The information gleaned from the wind-tunnel tests helped calculate the best posture and position for wheelchair racing athletes, but it also contributed to the development of a new chair scheduled to debut at next year’s Paralympic Athletics World Championships — the first British chair with an all-carbon-fibre chassis.
The advantage of using carbon fibre to make the chair, which is being developed by wheelchair manufacturer Draft, is that the frame is six times stiffer than a conventional aluminium one and therefore reduces drag because it doesn’t deform as the athlete pushes the wheels. According to the company’s co-founder Dan Chambers, however, the trend towards personalisation means that a fully carbon-fibre chair might never emerge as it would be too expensive to build individually designed seats from the material.
Instead, future improvements may come from reducing friction by changing other elements of the chair, he said. ‘On the track, they’re essentially using bike tyres, which are optimised for tarmac or velodromes — hard, reliable surfaces rather than the squidgy running surfaces the athletes go on. Similarly, there’s the actual pushing of the chairs. The athletes don’t grip the wheels; they’re actually punching or clipping them. There’s the possibility for losses in that system so if that was improved it would be faster for the athletes.’
When it comes to prosthetic limbs for sports, there is already a requirement that the technology literally be fitted to meet the user’s individual circumstances. The length and condition of the stump and whether any joints remain all have to be taken into account, as do the actions the athlete will be performing, which can have a huge effect on the basic design of the prosthesis. The famous blades worn by Peacock, Pistorius and others are specifically designed for sprinting and are the equivalent of forcing the athletes to stand on their toes, so long-distance runners need limbs with an ankle mechanism to better absorb the shock from the ground and prevent fatigue.
With blades becoming a standard tool for top amputee runners and carbon fibre the preferred material for many prostheses, developers are now finding more ways to optimise them for each athlete. ‘People like to compare [prostheses design] to Formula One but I prefer to compare it to cycling,’ said Kevin Harney, Asia regional president for manufacturer Otto Bock. ‘We’ve seen the development of bikes with carbon-fibre frames but ever since then it’s been about enhancing the design, improving the streamlining and not necessarily changing materials or the device.’
The obvious way this can be done is by tweaking the materials’ properties during manufacturing. ‘Different composites have enabled manufacturers to make devices that are bespoke to a person rather than a category of off-shelf items with a particular shape,’ said Saeed Zahedi, the technical director of prostheses manufacturer Blatchford, who recently chaired a discussion on sports prostheses at the Royal Academy of Engineering’s sports innovation conference.
‘The forces generated in terms of energy stored and returned need to be tailor-made to the athlete’s ability. Shape is one thing and another is the number of layers of composite, which we layer up to create maximum spring ability to absorb the energy at the right instant.’ The use of nanotechnology and an improved understanding of the micro level of composite layout could help this process progress even further.
Another area where manufacturers are hoping to improve the use of materials is in the interface between the prosthetic and the stump. One of the key functions of the socket is evenly distributing and reducing the high pressure, friction and heat on the stump. There’s also the problem of sweat, which adds to friction and encourages tissue damage; it also encourages bacterial growth. To counter this, Blatchford has developed a silicon material that can be laser drilled to create a design that drains sweat away from the interface. The company hopes to make the new socket available next year and is also developing continuous pressure-mapping technology that could improve interfaces further.
The ultimate interface could come in the form of osseointegration, where the prosthesis is connected to an implant attached directly to the bone. But this has yet to take off in sports prosthetics, partly because of the difficulties of maintaining the tissue and preventing infection around an implant that sticks out through the skin, although engineers at University College London are trialling technology based on deer antlers. In the meantime Icelandic company Össur, which developed the Flex-Foot Cheetah running blades used by Pistorius, is looking at another interface design to help improve control over the prosthesis.
The concept is based on the idea of squeezing the muscle through holes in the outside of the socket, enabling a tighter grip on the limb. ‘What we need is a different thought on the total contact area,’ explained Thorvaldur Ingvarsson, Össur’s head of research and development. ‘Today, the interface between the body and the prosthesis is based on total contact with the skin. Underneath the skin, we have the remains of the muscle and the bone. How do we activate the muscle and how do we get the muscle attached to the prosthetics? That’s the challenge.’
For prostheses that require joints, there is also the question of how to improve the mechanisms that enable athletes to move their limbs. One solution has come through the use of carbon fibre as a functional as well as a structural material, for example in the Otto Bock triangular foot that uses the flexibility of carbon fibre to move without a pivoting ankle joint. Another approach the company is taking is with an adjustable hydraulic knee, launched last year and used by German sprinter Heinrich Popow to win a gold medal in the T42 100m at London 2012.
‘Once the knee reaches the end of flexion, it has to be propelled forward so the athlete lands with it fully extended,’ said Harney. ‘Because there’s no control over the device, the knee has to go into full extension and then you need a damper in the last few degrees so it doesn’t create any shock. You still need a range of adjustment because each individual is different. Each damper, both flexion and extension, will have an adjustment screw that can be tuned. Once the athlete starts running, the hydraulics can adapt accordingly.’
Of course, an even more effective way to control joints is with electronic systems that use microprocessors to move in response to sensors within the prosthesis, and bionic limbs are already helping disabled people to lead more active lives than ever before. When it comes to competitive sport, however, this technology poses a problem as the Paralympics currently prohibits prostheses that move artificially. This is in order to ensure that the technology only serves to enable the athletes to reach their full physical potential and not to enhance their performance. Whether this will change is a point of contention for the industry.
‘My own view is you wouldn’t like to see cyclists with enhanced power on their bikes; you expect pedal power to be leg power,’ said Harney. ‘We’re at the stage where there won’t be any electronics introduced into the devices because it would give an unfair advantage and that takes away the credit to the athletes who do a lot of training.’
But Zahedi from Blatchford, which recently launched the first commercial biomimetic computer-controlled ankle system, argues that electronic control is simply the next step in tailoring prostheses to individual athletes and that the technology wouldn’t necessarily provide an unfair advantage because it still wouldn’t compensate entirely for the athlete’s disability.
‘My opinion is that the rules don’t stem from a true understanding of capabilities of the amputee and equipment,’ he said. ‘The future of prosthetics is integrated limb systems with different parts of the device talking to each other. Will microprocessors ever be allowed in the Paralympics? It depends on what sports you’re talking about. It’s about educating the regulators that it’s not always the case that microprocessor technology is good or bad.’
It seems unlikely the regulation of something as complex as bionic limbs will change any time soon, especially given recent controversy over the much simpler issue of blade length. But in some ways, the problem is just an extension of the basic difficulty of allowing athletes to compete using different prostheses. As the technology improves and spreads and we learn more about its effects on athletes, we may reach a time when Zahedi’s vision becomes reality. Or perhaps the Paralympics will have to create a new category: cyborg athletics.