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Dr Alan Wilson, Dr John Hutchinson, Dr Rachel Payne and Dr James Wakeling.
The Royal Veterinary College, University of London.

What limits the maximum gallop speed of a racehorse? The ability of animals, from an insect to a horse, man or dinosaur, to run fast is defined by physics and mechanics. From a mechanical point of view an animal's leg resembles a child's pogo stick, yet animals can run efficiently through a range of speeds and over a variety of terrains without bouncing.

This 'spring legged' gait is, however, inherently unstable and understanding how animals remain stable during motion is of interest both for its own sake and for the design of animal-inspired robots. Researchers at the Royal Veterinary College have developed equipment for studying animal motion literally 'in the field' (or indeed on the racetrack) with the aim of understanding the principles of each animal's system design for motion.

'The standard model for a racehorse is a man pushing a wheelbarrow', says Alan Wilson. 'The power is provided by the back legs and the front legs hold the animal up.' But it's more complex than that. Increasing power doesn't make a horse run faster. Using a combination of data collected from racehorses in training via global positioning systems and radio-linked sensors on the animals, plus computer simulation of horse locomotion, the team can show how a horse can gallop at over 40 mph, and which horse has the best potential to be a winner.

Horses actually fly more than run when they gallop, as their legs are off the ground for over 80% of the time. The muscular work of galloping horses is halved by storing and returning elastic strain energy in spring-like muscle-tendon units - the pogo stick mechanism - and is optimised to stretch and recoil at around 2.5 strides per second. The higher the frequency, the greater the speed.

A key ability for fast runners is to bring their legs forward for the next stance quickly in order to support their weight. This is a particular challenge for large animals with long limbs where muscles contract slowly and have a relatively low power output. 'Horses store energy in an elastic biceps muscle in the leg that releases energy to catapult the limb forward', explains Alan.

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