Chris Whitton, BVSc, FANZCVS, PhD, head of the Equine Centre at the University of Melbourne’s Veterinary School, in Australia, has been looking at correlations between injury risk and racehorses’ stride length, speed, and frequency.
Researchers know that repeated application of high loads to bones and resulting bone fatigue contribute to injury in racehorses. “Cyclic loading leads to structural damage in any material—it’s like the laws of physics, we can’t avoid it,” said Whitton.
Detecting the bone fatigue in time to prevent injury, however, has proven challenging, as no imaging device can predictably detect microdamage, he said.
Therefore, he hypothesized that monitoring horses’ stride parameters and looking for key changes in them could help identify horses at risk of impending injury.
In human sports athletes use GPS and accelerometers to monitor their workouts, especially at high speeds. “The benefits of doing this in horses is to educate trainers, inform decision-making, provide cost-effective constant monitoring, and detect injury risk early,” said Whitton.
In his initial study Whitton used a Stride Master device to collect data from 25,260 starts over five years (2011 to 2016) in Tasmanian racehorses.
In general, he noted that the faster a horse runs, the fewer strides he takes. Stride length and speed both decrease as a race progresses. Factors associated with stride include:
- Weight carried.
- Number of starts.
- Finishing position.
- Track type and firmness. Heavier (turf) tracks were associated with shorter stride length and greater stride frequency, said Whitton.
- Sex. “Female horses had shorter stride lengths, greater stride frequency, and lower catastrophic injury—probably due to their smaller size,” he said.
He identified longer races, firmer surfaces, and heavier weights as risk factors for injury.
“Reduced load has a greater effect on bone fatigue than a reduced number of strides,” said Whitton. “Each stride is a cycle of load. To reduce the number of cycles of load, you need to reduce the number of strides. Generally, this is achieved by reducing distance, whereas load is more associated with speed. So if you increase speed, you decrease the number of strides over a set distance, but you increase the load. Because load has a greater effect, then going faster increases stress on the skeleton.”
Whitton also assessed risk factors and stride changes prior to events such as injury, forced layoff, and retirement and found:
- An increased injury risk among horses that had completed either many or very few races.
- Injury risk increased 2.17 times for each unit decrease in speed in the final 200 meters of a race. Before injury, affected horses’ speeds dropped off much faster than a horse’s normal decline in performance, said Whitton.
- Injury risk increased 2.9 times for each unit decrease in stride length.
- No association between injury risk and stride frequency.
In summary, he said, “constantly monitoring speed, distance, and stride data might help predict injuries.”
Further, collecting speed and stride data can allow researchers to create equations for determining training and racing’s effects on horses’ skeletons.