The Effect of Training on Stride Duration in a Cohort of Two-Year-Old and Three-Year-Old Thoroughbred Racehorses

SIMPLE SUMMARY: Objective gait monitoring via GPS and motion sensors is becoming increasingly popular with racehorse trainers. This has the potential to assist in early detection of lameness and performance issues. This study sought to identify normal changes in gait in a population of two and three-year-old racehorses in order to inform future studies. We found that horses decrease their stride duration at a given speed over time with training. Stride duration appears to increase with increased distance galloped, but this effect is reduced over a training season and presumably increased fitness, so this may serve as a useful indicator for fatigue. ABSTRACT: Objective gait monitoring is increasingly accessible to trainers. A more comprehensive understanding of ‘normal’ gait adaptations is required. Forty two-year-old thoroughbred racehorses were recruited when entering training and followed for 22 months. Gait analysis was performed by equipping each horse with an inertial measurement unit with inbuilt GPS (GPS-IMU) mounted on the dorsum. Horses were exercised as per their regular training regimen. Data were analysed using a linear mixed model. For two-year-old horses, there was a non-linear pattern of stride duration (SD) over time (p < 0.001) with SD decreasing initially and then ‘flattening off’ over time (linear and quadratic coefficients −0.29 ms/week and 0.006 ms/week(2)). Horses showed an increase in SD of 2.21 ms (p < 0.001) per 100 m galloped, and over time, SD decreased by 0.04 ms (p < 0.001) with each 100 m galloped per week. Three-year-old horses overall showed no change in SD over time (p = 0.52), but those that had a period of time off showed a decrease in SD of −0.59 ms per week (p = 0.02). They showed an increase in SD of 1.99 ms (p < 0.001) per 100 m galloped, and horses that had a period of time off showed an increase in stride duration of 1.05 ms per 100 m galloped (p = 0.01) compared to horses which did not have time off. Horses demonstrate an adaptation to high-speed exercise over time. SD decreases with training when other factors are controlled for in naïve horses.