WILSON,, A.M.*; WITTE,, T.H.; PFAU, T.; ROBILLIARD, J.J.; The Royal Veterinary College & UCL, London; The Royal Veterinary College, London; The Royal Veterinary College, London; The Royal Veterinary College, London: Kinematics of high speed locomotion in the horse

The thoroughbred racehorse can gallop at over 18ms^-1 during racing and hence represents an excellent model for studying adaptations for and limitations to high speed locomotion. Most gait studies however focus on less athletic horses on treadmills at lower speeds. We have developed techniques for studying locomotion of fit racehorses in the field during their normal training regime. The goal was to determine peak limb loads and the effect of speed on mechanical energy changes. We determined time of foot on and off using foot mounted accelerometers and trunk movement using an inertial sensor (three accelerometers, three gyroscopes and three magnetometers). Data were transmitted through five radio telemetry links and logged onto a laptop computer. Speed was determined using a GPS data logger. Data were recorded from nine horses on a level dirt racetrack. Here we present data recorded at 9ms^-1 and at 17ms^-1. At the higher speed stance duration decreased from 123ms to 82ms (front) and 134ms to 91ms (hind). Protraction duration dropped from 375ms to 341ms and 369ms to 339ms for front and hind limbs, respectively. At 17ms^-1 duty factor ranged (between horses) from 0.17 to 0.23 (mean 0.19) for the front limbs and 0.20 to 0.23 (mean 0.21) for the hind limbs. Assuming a sinusoidal vertical ground reaction force this predicts peak limb forces of 23.6 Nkg-1 for the front limbs and 15.7 Nkg-1 for the hind limbs. The inertial sensor data were used to calculate angular and linear displacement of a point approximating to the position of the centre of mass. The range of roll angle (amplitude) increased from 8.1� at 9ms^-1 to 13.0� at 17ms^-1, pitch range increased from 12.6� to 19.8� and yaw range increased from 5.4� to 7.0�.