Are toe grabs the leading cause of racehorse breakdowns? Sharp increases in racehorse foreleg injuries is a hot topic and a recent study points a finger at toe grabs, racetrack surfaces and horse fatigue.
Research conducted by engineer G.W. Pratt of Massachusetts Institute of Technology (MIT) published in the Equine Veterinary Journal concludes that toe grabs, racehorse fatigue and racetrack surface conditions are the primary culprits of racehorses breaking down during races and training. This conclusion contradicts the notion that racehorse breakdowns are largely the result of foreleg overloading, congenital bone deformities and poor nutrition.
Pratt’s study involved cementing a highly sensitive singleaxis accelerometer to the front of a racehorse’s hoof wall. Data was taped on a high-speed recorder carried by a jockey on a racetrack at racing speeds of 16.7 meters per second.
In order to detect variations between racetrack soil conditions, Pratt took high-speed film footage at various other racetracks and analyzed soil samples from 11 tracks for size, moisture-density relationship and angle of internal friction.
Accelerometer data was analyzed to determine peak loads and acceleration patterns of a foreleg as a racehorse picks up speed out of the gate. The critical part of each stride was found to be within the first 10 to 20 milliseconds after ground contact, as the hoof slides forward and stops. This abrupt stop places a foreleg hoof under tremendous load, leading to the leg breaking down.
Pratt concludes that bending forces exerted on a foreleg–not overloading–are the primary sources of racehorse injury. Combining data gathered from this study with data from past studies, the engineer determined that peak load forces on the foreleg cannon bone are “only approximately 50 percent of the ultimate strength. Hence the peak axial load is an unlikely cause of fracture of the metacarpal bone.”
Pratt’s analysis places average deceleration of a hoof as it slides to a stop at an astounding 91 to 117 G-force, placing the leg under enormous bending force. “Such large nonaxially directed forces are very probably of critical importance as a source of injury,” Pratt concludes.
Pratt’s findings parallel the results reached by Albert Kane’s 1996 study which determined a strong link between high toe grabs and racetrack injuries. Kane concluded that rim shoes put racehorses at significantly less risk than shoes with toe grabs.
Pratt states “injuries to the foreleg increase by huge factors for horses shod with regular toe grabs compared to horses shod with flat shoes ... The strong correlation between shoe type and incidence of injury supports the proposition that the process by which the hoof enters the track and comes to a stop is of critical importance. This, of course, does not exclude other contributing factors such as irregular surfaces or torsion.”
Soil And Fatigue
Pratt also analyzed how racetrack soil composition and racehorse fatigue contribute to foreleg injuries.
By analyzing the shear strengths of various track surfaces and the horizontal forces they place on a horse’s foreleg, Pratt concludes that “choosing a rounded sand or providing adequate thatch on turf courses is very important as a means of lowering injury rates.”
Previous studies have determined that as a racehorse picks up speed, a torque develops that shifts weight from front to rear with minimal resistance and vertical loading. Pratt labels this torque as a “self-protective mechanism of the stride” and data from Pratt’s study determines that “as the horse tires, this torque-related protective mechanism of the first fore becomes less and less effective.”
Pratt’s conclusion states the following: “It has been argued that the forelegs of the horse are at greatest risk when they first enter the track. That risk can be reduced by adequate depth of low-friction soil on a dirt track and adequate thatch on turf. Gripping attachments on the shoes seriously compromise the (horse’s) safety. Fatigue decreases the capability of shifting weight to the rear and also shortens the time available to retract the leg while in the air, which can cause it to enter the surface too rapidly.”
In other words, don’t blame the recent rash of racehorse breakdowns on bone deformities, overloaded limbs or poor horse nutrition. Instead, investigate ways to eliminate high toe grabs on shoes, choose the proper track surfaces and condition horses better.