Meeting Abstract

14.2  Thursday, Jan. 3  What limits running speed in race horses SPENCE, A.J.*; WILSON, A.; Royal Veterinay College; Royal Veterinay College aspence@rvc.ac.uk

During thoroughbred horse racing equine athletes strive for maximum performance. As a result, the level of effort of horses during racing can be considered to be roughly constant, and of the highest achievable intensity. However, the factor or combination of factors that limit maximum horse speed remains elusive. Hypotheses include a limb force limit, a metabolic power limit, and some form of mechanical constraint, either in limb protraction or in the animals� interaction with the substrate. Recent work has shown that another quadruped, the dog, is not force limited, and there is evidence to suggest that horses, unlike humans, are unable to significantly vary their effective leg stiffness. This makes them an attractive model system in which to examine the limitations to running speed. Here we test the hypothesis that horses are limited by their ability to adjust their mechanics for a compliant surface. We utilize a large, novel data set collected from a wireless RF tracking system (TurfTrax Racing Data Ltd., UK). Highly accurate position and speed information for all horses throughout each race, with accompanying race course topology and surface condition measurements, were analyzed for 30,932 horse starts in 2,667 races, spanning the 2006 season. We examine the speed and hence energetic requirements of the horse as a function of inclination, declination, and surface properties. A simple analytic approximation was used to compute the work done in deforming the surface. The power exhibited by the race horse in running up an incline is larger than the estimated cost of deforming the softest surface, suggesting that the mechanical interaction of the surface and animal, and not the rate of work production, may be the critical factor in determining maximum horse speed.