How Paralympic Wheelchairs and Prostheses Are Optimized for Speed and Performance
By Sophie Bushwick, Scientific American
As audiences across the world tune in to the Tokyo 2020 Paralympic Games, they will see athletes using an impressive array of high-tech prosthetic limbs, wheelchairs and other assistive technology. These devices bear little resemblance to those for everyday use—and vary a great deal from sport to sport.
“We design sporting equipment to get the best possible performance based upon the constraints and needs of that sport,” explains Bryce Dyer, a sports technologist at Bournemouth University in England, who develops prostheses for athletes with disabilities.
For example, blade-style prostheses—which are springy to better store and release energy—have become well known in track-and-field events. But people with lower-limb amputations who compete in cycling events have to perform a different type of motion at much higher velocities, so their prosthetic limbs have different requirements. “One of the greatest forces that slow you down when you get above a certain speed is that of aerodynamic drag. And the more drag there is, the more effort you have to apply to try and mitigate for and overcome it,” Dyer explains. The legs of nondisabled people are “not particularly aerodynamic; they’re not designed for that task. But a cycling prosthesis, we can design it that way.” He has created such items with a flat middle section in place of the lower leg. “We can make it very, very thin,” Dyer says, “almost like an aircraft wing—razor-blade thickness—to slice through air [and] reduce or remove any turbulence from it.” For cycling limbs, this flat section is oriented so the thin edge faces forward, as opposed to blade prostheses for running, in which the broad side does so.
Wheelchairs for different sports also vary widely, although they share some similarities. Many are built from high-tech materials, such as carbon fiber, that make them both strong and lightweight. They often include rubber-coated wheel-turning grips that athletes grab with gloved hands to maximize friction. But beyond that, the designs diverge. In wheelchair fencing, for example, the wheels are locked into place while athletes strike and dodge from set positions. So fencing chairs are equipped with leg straps and sturdy handles that help the athlete stay solidly seated. And many have a lower than usual back to enable more upper-body movement.
The basic shape of a fencing chair still looks a lot like that of an everyday wheelchair. But this is not at all the case with racing chairs, which are built for high speeds. A third wheel in the front of such a device enables a low, elongated shape, which works optimally with the athlete’s position: kneeling and leaning forward. Spoked wheels are usually swapped out for smooth disks that generate less air turbulence, reducing the effort required to move at high speeds.
For sports that require more maneuverability, yet another design element is required. “Your tires or your wheels are actually slanted,” says retired American wheelchair basketball player Becca Murray, who has participated in three Paralympic Games and won gold at two of them. “And the dynamic of that is that it helps you be faster, and you’re able to turn quicker on the dime, whereas your everyday chair—it doesn’t let you turn as sharp.” Additional wheels on the back of the chair also help with these speedy turns and add stability. But such chairs do sometimes tip over, so designs must be sturdy. This is also why athletes wear straps or belts across their hips and legs. “If you were to fall over, you want to be able to just get right back up,” Murray says. “So you want your wheelchair to stay attached to you, almost like you’re one with the wheelchair.”
In addition to suiting a specific sport, a device must serve each athlete’s unique needs. “Most of the equipment is custom-made: it’s designed to get the most out of that individual athlete’s physical body,” says Ian Brittain, an associate professor of disability and Paralympic sport at Coventry University’s Research Center for Business in Society in England. For instance, prosthetic legs for track and field may or may not include mechanical knee joints. “Some runners, depending on the length of their limb, will have a knee joint added” if they have an above-the-knee amputation, Dyer says. “But there are some unique athletes, and a good example of that is the British athlete Richard Whitehead.” Whitehead has two above-the-knee amputations and has developed his own running style—one that does not require knee joints at all. “It looks almost like an egg whisk, where he almost brings his legs around in a whisking pattern, left- and right-hand side,” Dyer says. “That’s very unique to him.”
Among athletes who compete in wheelchairs, similar customization is necessary. For instance, increasing the height of the chair’s back and the slope of its seat, also called the “dump,” can help compensate for abdominal weakness. “I actually have a little dump in my chair because I don’t have all my core muscles to help me with that balance,” Murray explains. “It just means that my knees are higher than where I’m sitting, so it’s on an incline.” Players with injuries high on their spine may have less abdominal strength than Murray and require a dump even in their everyday chair. Others with amputations or knee injuries may have more abdominal strength and not need a dump at all.
The technology seen at the Paralympics can increase speed and mobility in sports—but it is unlikely to inspire visibly different designs for nonathletes. One reason is that the wheelchairs used in daily life are already optimized for other qualities, such as taking up as little space as possible. “You want your everyday chair to be the smallest it can be, because in everyday life, you have to get through little places and doorways and things like that,” Murray explains. “You like it to fit snug on your hips, and the wheels are straight up and down so that you can be as narrow as possible.” Many public spaces are simply not built to accommodate a variety of wheelchair designs.
Price is another consideration. “You have to bear in mind the commercial market for elite athletes is incredibly small, and in many cases, those athletes are sponsored,” Dyer says. “So it is important to have some degree of trickle down in the same way that IndyCar or Formula One technology does eventually trickle down to everyday family cars. But sometimes it’s quite subtle.” For example, some scarcely visible component of a prosthesis—such as the socket that attaches the limb to the wearer’s body—may improve.
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