"Injuries and fatalities are a major problem in the (Thoroughbred) racing industry," said Jacob Setterbo, BS, a graduate student at the University of California, Davis, during the 2008 American Association of Equine Practitioners convention (held Dec. 6-10 in San Diego, Calif.). "There are about two racing-related equine deaths per day due primarily to musculoskeletal injury (in the U.S. and Canada)."
Thus, there is great interest in any factor that can reduce the risk of musculoskeletal injury, such as track surface--which was the topic of Setterbo's presentation.
Until now, most epidemiologic studies on track surface type and injury rates have been confounded by varying conditions at different track locations, said Setterbo. He presented the results of a study conducted at a single racecourse (Keeneland in Lexington) directly comparing the effects of dirt, turf, and a synthetic surface (Polytrack) on hoof acceleration and ground reaction forces (impact). The theory is that lower acceleration and ground reaction forces might help reduce injury rates.
For this study, four 3-year-old Thoroughbred fillies wore an acceleration measurement package and a force-measuring shoe on their left forefeet during trot and slow gallop trials (horses moving at about 3 meters per second and 6 meters per second, respectively). The horses' speeds and number of trials were limited to avoid fatigue.
"The synthetic surface had the lowest values for most peak ground reaction forces, acceleration, and mean vibration variables," Setterbo reported. "The synthetic surface maximum deceleration during the hoof landing phase of stride was 81% of the dirt surface maximum and 66% of the turf surface maximum. Turf had the highest landing decelerations; likely it is more resistant to the hoof digging in when landing and pushing off."
He cautioned that since only forelimbs were evaluated, and at speeds that were significantly slower than racing speeds, the results might not be directly applicable to racing speeds. He also advised that based on significant differences between footing materials, weather, and maintenance programs between tracks and regions, "extending the results of this study to encompass all synthetic track surfaces should be done with caution. We are just scratching the surface with this study, but the comparative results do look promising to start."