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The Flex-Foot Cheetah works by storing and releasing energy within a carbon fibre sprinting foot, a prosthetic that mimics the reaction of the anatomical foot/ankle joint to allow amputees to run quickly and naturally. The foot is J-shaped and resembles the hindquarter of a cheetah, acting like a spring and shock absorber combined. As the unit is compressed on impact, energy is stored and stress absorbed within it – which would otherwise be transferred directly to the user’s knee, hip and lower back – before being released into the ground at toe-off to propel the user forward.
The foot’s design is revolutionary, with areas of high stress – such as the apex of the J-curve – fitted with more layers of carbon fibre, while areas in need of greater flexibility are fitted with less, allowing for a dynamism that would not be possible with a singlesized material. Further, due to the fact that the Flex-Foot Cheetah has no heel, the wearer is constantly positioned on the balls of their feet, accurately mimicking how an ablebodied runner sprints. Importantly, however, while the system is refined and has allowed amputees to rack up many world records, due to its passive nature – the foot has no motors, sensors or microprocessors – the Cheetah only returns 80 per cent of the energy stored during compression, a far way off the 249 per cent of a normal, able-bodied foot/ankle/gastroc system.