Marathon feat

Running the London Marathon is a major achievement for anybody, but taking part on crutches raises the achievement to another level.

Engineering student Peter Snell was all set to run for the charity CRY (Cardiac Risk in the Young), and had secured pledges of 4,500, when he broke his ankle during a training run just two months before the race. Still determined to compete, he asked the charity if it could help. The best option seemed to be for Snell to 'run' the race on crutches, using his good foot and the crutches to swing himself forward. But clearly, normal crutches wouldn't do.

After a fruitless search for racing crutches, CRY put him in touch with REMAP, an organisation which designs and constructs customised technological aids for the disabled. REMAP works through a network of volunteer engineers, and the task of designing Snell's crutches was entrusted to Harry Thomson, a former RAF engineer who now runs Top Flight Tasking, an Oxfordshire company that makes remote-controlled vehicles for use in bomb disposal and the nuclear industry.

Thomson determined that racing crutches would need to have three features not found in standard crutches - some sort of protection for the rubber tips of the crutches, to stop them wearing away on the road surface, as this would increase vibration; better padding on the grips, so that Snell's hands would remain comfortable and wouldn't blister; and an integrated shock absorber to prevent shock travelling up the crutch into his arms and shoulders.

Thomson inserted tungsten carbide pads into the tip of the crutch to provide extra protection and grip on the road surface, and a memory foam coating on the handles of the crutches to mould to Snell's fingers. this both increased the grip comfort and provided an extra layer of vibration damping. But for the built-in shock absorber, he turned to another engineering specialist.

The best form of damping for the crutches, Thomson decided, were gas springs. These could be inserted into the shaft of the crutch, where they would compress as the crutch hit the ground, absorbing the impact energy, and release as Snell raised it. These would be combined with a rubber insert on the crutch shaft which would limit the amount the spring would compress, tailoring the performance to Snell's height and stride pattern.

Thomson turned to Industrial Gas Springs in Surrey, which produces pneumatic springs which compress the working gas. However, the springs had to be precisely 'tuned' to Snell's weight, which is more difficult than it sounds.

in a training run, the gas pressure was set too high, resulting in him having to fight the springs. An attempt to change the pressure resulted in the level being set too low, which meant that the crutch shaft bounced off the rubber insert, which led to Snell injuring his wrist.

Fortunately, IGS was able to provide a new set of springs, which arrived and were fitted 48 hours before the race. 'The results were amazing,' said Snell. 'I no longer had to fight against the springs on the compression stroke and, with the introduction of some other new design features, the updated crutches were simply brilliant.' The 26.2-mile course required the springs to withstand around 30,000 compression and extension cycles, helping to propel Snell to the finish line in 8hr 18min 58sec - some distance from his personal best on both feet, but possibly even more of an achievement.