Musculoskeletal injury is the main cause of wastage in Thoroughbred racehorses worldwide, with nearly 30% of all fractures being pelvic and tibial stress fractures. California studies in the late 1990s suggested fast work increased the risk of injuries, while Kentucky studies implied high-speed exercise was protective. K.L.P. Verheyen, DVM, MSc, PhD, MRCVS, of the Royal Veterinary College (RVC) in London, examined risk factors for pelvic and tibial stress fractures at the Animal Health Trust in Newmarket.
"If we can identify modifiable risk factors for injury, we might be able to reduce the incidence of injury," Verheyen says. Thirteen trainers in England participated in the study of nearly 1,200 Thoroughbreds (mostly 2- and 3-year olds) that were in flat race training. From 1998 to 2000, trainers kept daily records on exercise distances, speed, and surface quality, and they noted injuries. There were 148 fractures, including 41 pelvic and tibial stress fractures.
Training methods were associated with injury risk. "The take-home message, as far as pelvic and tibial stress fractures are concerned, is that too much slow speed exercise is not good," she says. "We know that stress injuries are repetitive loading injuries. If you keep doing the same thing again and again, you risk injury. We compare it to a paper clip. If you bend it and bend it, it will break. It's material fatigue. Interval training (alternate periods of hard exertion and rest) is a better option because high-speed exercise is as not bad as previously thought. It actually stimulates bone to respond, because bone is a living tissue and is constantly remodeling.
"High-impact exercise stimulates the bone to adapt to the loads it must tolerate," she says. "If the same exercise is repeated again and again, the bone will stop responding, which is what we think is happening with the low-speed exercise and stress fractures." For more information see www.TheHorse.com/emag.aspx?id=6708.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.