Stride changes a sign of increased breakdown risk in racehorses – study

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Findings raise the prospects of monitoring stride characteristics over time in a bid to intervene before musculoskeletal injuries occur.
Image by Calvin Tatum

Decreasing speed and a shortening stride length over multiple races is associated with musculoskeletal injuries in racehorses, Australian researchers have found.

The findings in the University of Melbourne study raise the prospect of monitoring stride characteristics over time in a bid to intervene before musculoskeletal injuries occur.

Adelene Wong and her fellow researchers, writing in the Equine Veterinary Journal, noted that certain stride characteristics have been shown to affect changes in biomechanical factors linked with injuries in human athletes.

Considerable research has been directed toward musculoskeletal injuries in racehorses, they said. There is now considerable evidence that catastrophic injuries arise because of bone fatigue, which accumulates over multiple galloping events.

“This gradual onset provides the opportunity to identify injuries prior to their occurrence. Because a high proportion of musculoskeletal injuries in racehorses develop over time, it is likely that changes in gait could be useful to detect an impending injury,” they said.

This led to their study, which sought to determine whether changes in race-day speed and stride characteristics over career race starts are linked with greater injury risk.

Speed, stride length, and stride frequency data were obtained from the final 200-metre section of 5660 race starts in Tasmania by 584 horses, comprising 146 horses who went on to suffer a race-day musculoskeletal injury, and 438 controls, who did not.

The study team found a gradual increase in the risk of musculoskeletal injury with each 0.1 metre per second decrease in speed. The risk also gradually increased for each 10-centimetre reduction in stride length over time (career race starts).

A more marked rate of decline in speed and stride length was identified about six races before the injury.

Discussing their findings, the authors said they observed a decrease in speed and stride length, but not stride frequency, over career race starts in association with increased risk of race-day injury. “This was despite a general trend for increasing speed and stride length with greater numbers of career starts for all horses,” they said.

“These findings highlight the potential of speed and stride monitoring during races for injury prediction.”

However, the risk of musculoskeletal breakdown was in fact highest early in the horse’s racing career, peaking at the second race. This suggested that additional monitoring of training workloads may be needed for predicting these early career injuries.

The researchers said their findings align with previous studies which showed that horses in their first year of racing were at increased risk of fatal lower leg fractures.

“However, a greater number of starts is also associated with an increased risk of musculoskeletal injury as we similarly observed in this present study beyond approximately 15 career starts.”

The study team said the link between increasing horse age and an increase in injury risk is likely because of the accumulation of damage with longer racing careers.

“Current research points towards two differing pathways to injury whereby bone damage could occur when loading is introduced too rapidly to a poorly adapted skeleton or when racing or training duration and intensity exceed the capacity of a well-adapted skeleton.”

Injuries early in a horse’s career are hypothesised to occur for the first reason, while those that occur later would likely have occurred due to the latter pathway.

The authors said modifying a horse’s training and/or racing schedule when a consistent decrease in speed and stride length across several races is observed could be crucial in preventing some musculoskeletal injuries.

“Detecting changes in race stride characteristics over time requires horses to have a minimum number of starts; however, in the current study 28% developed injuries within the first three races of their career, limiting the use of this technique in this group.”

There were too few deaths among the injury group to draw definitive conclusions about the usefulness of speed and stride data for predicting fatal injuries. Two out of nine horses in the study group suffered their fatal injury before accumulating enough starts to determine a typical stride pattern, and one horse’s stride was not monitored throughout its career before its fatal injury. Three of the remaining six showed an overall decrease in speed and stride length in the six to eight races before injury.

The study team said the wider use of inertial sensors to monitor horses in training and racing would provide valuable datasets for further investigation. This method would be most promising for horses that develop injuries later in their careers, when more data would be available for analysis.

Accounting for time between race starts and competing risk events will be central to further improving the models to predict injury, they said.

The full study team comprised Wong, Ashleigh Morrice-West, Chris Whitton and Peta Hitchens, all from the University of Melbourne.

The study received funding from the Grayson-Jockey Club Research Foundation, Tasracing, Racing Victoria, the Victorian Racing Industry Fund, and the University of Melbourne.

Changes in Thoroughbred speed and stride characteristics over successive race starts and their association with musculoskeletal injury
Adelene S. M. Wong, Ashleigh V. Morrice-West, R. Chris Whitton, Peta L. Hitchens
Equine Veterinary Journal, April 28, 2022, https://doi.org/10.1111/evj.13581

The study, published under a Creative Commons License, can be read here

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