Simulated effects of racetrack material properties on the vertical loading of the equine forelimb

Abstract

One of the factors cited as contributing to racing injuries of horses is the condition of the racetrack surface. This study examines the possible effects of different dirt racetrack surfaces by using dynamic modelling of the horse and track to quantify the vertical loading of the hoof and coffin joint. Results indicate that as the stiffness of the racetrack material increased from a weak soil to a rock surface (constant soil damping ratio of 15% of critical damping), the maximum track deflection decreased from 5.1 to 1.2 cm; stance phase duration decreased by 60%; energy dissipation decreased by 72%; maximum vertical ground reaction force and coffin joint force increased by 19% and maximum vertical rate of loading increased by 219%. Varying the soil damping ratio from 5 to 30% of critical damping had only small effects on the loading response, changing the above parameters by less than 5% for the medium soil type simulated. These results indicate that the track surface may have a profound effect on the loading conditions of the horse’s limb, with the surface stiffness properties having a greater effect on loading than the surface damping properties. Design of appropriate race track surfaces may therefore be more dependent on selection of soil for structure, rather than soil amendments which have been used primarily to alter damping characteristics.