Out on a Limb
Development
Cyclists
Even for the able-bodied cycling is an unnatural thing to do. Moving the feet in a pair of circles, with the two feet at opposite points in their respective circles, bears little resemblance to any gait of any bipedal or quadrupedal animal. Neither gravitational nor elastic energy storage, used in normal walking and running, play much of a role. About the only "normal" aspect of cranking a bike is the opposite movements of the two legs and the use of the powerful extensor muscles.
COP Outcome development and evaluation
Cyclists obsess over their pedalling action and spend years perfecting what has been described as "the classical ballet of graceful pedalling". Cyclists lacking finesse stamp on their pedals, "chopping" them up and down, wasting energy; a good cyclist pedals in neat, fluid circles, maximising power transmission. The trick lies in the ankle – as the foot goes round, the toe moves from being level with the heel to a toe-down attitude at the top and bottom of each cycle. Mark Inglis' walking limbs stayed fixed through the cycle, giving him appearance of a waddling duck as he pedalled.
Wayne Alexander modified a pair of American legs, giving each foot a 15-degree downward rake toward the toe. Despite Mark's initial skepticism, the modification produced immediate results: he gained ninth place in the 16km time trial at the Paralympic World Cycling Championships. (In his recent book No Mean Feat Mark confesses he abandoned the legs at a New York airport, rather than pay exorbitant excess baggage charges – something Wayne still can't quite bring himself to talk about.)
Encouraged by the success of the concept, Wayne created a new pair of racing legs with aerodynamic carbon-fibre twin spars and a polymer "ankle", which Mark used at the 1999 Southern Cross Multidisability Games in Sydney. (After the event these legs found a permanent home at Te Papa). A third set, with toe-axis movement, was built for the Sydney 2000 Paralympic Games, where Mark won a silver medal in the 1km time trial.
In these legs, the pedal cleat bolted directly onto the footplate, doing away with the need for a shoe and reducing the rotating mass by about 400gm; but the key advance was the movement of the foot-plate relative to the pedal. As the foot passed through the bottom of the cycle, a spring in the plate flung the foot into a toe-down position, shortening the time spent in the null or dwell spot, where the leg is neither pulling or pushing.
