The mechanics of the running blades used by South African former Paralympic runner Oscar Pistorius depend on special carbon-fiber-reinforced polymer prosthetics. Pistorius has double below-the-knee amputations and competed in both non-disabled and T44 amputee athletics events. Pistorius's eligibility to run in international non-disabled events is sanctioned by the International Association of Athletics Federations (IAAF). Pistorius began running in 2004 after a rugby knee injury which led to rehabilitation at the University of Pretoria's High Performance Centre with coach Ampie Louw. His first racing blades were fitted by South African prosthetist Francois Vanderwatt. Because he was unable to find suitable running blades in Pretoria, Vanderwatt ordered some to be made by a local engineer at Hanger Orthopedic Group. These quickly broke, and Vanderwatt referred Pistorius to American prosthetist and Paralympic sprinter Brian Frasure to be fitted for carbon-fibre blades by Icelandic company Össur. Pistorius's participation in non-disabled international sprinting competitions in 2007 raised questions about his use of running blades, and the IAAF amended their rules to ban the use of "any technical device that incorporates springs, wheels or any other element that provides a user with an advantage over another athlete not using such a device." After initial studies, Pistorius was ruled ineligible for competitions under these IAAF rules. After further research was presented, the Court of Arbitration (CAS) ruled that his running prostheses were not shown to provide a net competitive advantage over biological legs. In 2012, Pistorius qualified for and competed in both the 2012 Olympic Games and the 2012 Paralympic Games using his running blades, becoming the first amputee sprinter to run in the Olympic Games.
Pistorius's athletics prostheses The blades are transtibial prostheses, meaning they replace legs and feet that are amputated below the knee. They were developed by medical engineer Van Phillips who incorporated Flex-Foot, Inc. in 1984. In 2000, Van Phillips sold the company to Össur which, as of 2012, still manufactures the blades. They are designed to store kinetic energy like a spring, allowing the wearer to jump and run effectively.
Carbon fibre is actually a carbon-fiber-reinforced polymer, and is a strong, light-weight material used in a number of applications, including sporting goods like baseball bats, car parts, helmets, sailboats, bicycles and other equipment where rigidity and high strength-to-weight ratio is important. The polymer used for this equipment is normally epoxy, but other polymers are also used, depending on the application, and other reinforcing fibres may also be included. In the blade manufacturing process, sheets of impregnated material are cut into square sheets and pressed onto a form to produce the final shape. From 30 to 90 sheets may be layered, depending on the expected weight of the athlete, and the mold is then autoclaved to fuse the sheets into a solid plate. This method reduces air bubbles that can cause breaks. Once the result is cooled, it is cut into the shape of the blades. The finished blade is bolted to a carbon fibre socket that is an intimate fit to each of Pistorius' legs. These are custom made and make up the bulk of the total cost, along with the assessment and setting up of the finished prostheses. Each limb costs between $15–18,000 USD. Pistorius has been using the same Össur blades since 2004. He was born without fibulae and with malformed feet, and his legs were amputated about halfway between knee and ankle so he could wear prosthetic legs. He wears socks and pads which are visible above the sockets to reduce chafing and to prevent blisters, and the sockets have straps in the front that can be tightened to make the prosthesis fit more snugly. Pistorius uses custom-made spike pads on the blades. Before development of the pads, his spikes were changed by roughing up the surface and applying over-the-counter spikes by hand, but the results using this method were inconsistent. Research was conducted in Össur's Iceland lab using a pressure-sensitive treadmill and film at 500 fps to measure the blade strike, and produced a spike pad which includes a midsole of two machine-molded pieces of foam of different densities to cushion impact, with a carbon fibre plate on the bottom. The developers attached the pad with contact cement, which can be quickly removed with the application of heat when the spike pad needs to be changed. Because of the curved design, the blades have to be slightly longer than a runner's biological leg and foot would be. The blades replace the hinge of an ankle with elastic compression that bends and releases the blade with every stride, so the uncompressed blade leaves the user standing on tiptoe. They are designed to move forward, so have no heel support in the back. According to Josh McHugh of Wired Magazine, "The Cheetahs seem to bounce of their own accord. It’s impossible to stand still on them, and difficult to move slowly. Once they get going, Cheetahs are extremely hard to control."
How the blades work
… excerpt ends here. Continue reading the full article.
