Ferrari, M.; Pfau, T.; Wilson, A.M.; Weller, R. Equine Veterinary Journal May 2009 41 5 493-497(5) Reasons for performing study: The influence of training on stride parameters is controversial and to date there is no information on how training influences stride parameters during high-speed locomotion in the field. Objective: To determine the influence of training on stride variables during high-speed locomotion in Thoroughbred racehorses. Methods: Speed, stride frequency, stance and protraction times were quantified in 8 Thoroughbreds with foot mounted accelerometers and GPS sensors during their first week of canter after the summer break and 6 months into training. Results: At a speed of 11 m/s, stride frequency was (mean ± s. d.) 2.160 ± 0.120 strides/s pre- and 2.167 ± 0.083 strides/s post training; mean stance time was 125.3 ± 9 ms pre- and 125.9 ± 7 ms post training; protraction time was 340.7 ± 20.4 ms pre- and 337.2 ± 14.3 ms post training. The increase in stride frequency and the decrease in protraction time after training were significant. There was no statistically significant difference in the maximum speed reached by each horse pre- and post training. Conclusions: Stance time stayed constant throughout the training season in the tested horses. A significant decrease in protraction time and a corresponding significant increase in stride frequency were observed after training. Potential relevance: Training of racehorses could be adapted to maximise the effect on modifiable parameters and reduce the risk of training-induced pathologies. Further research will be conducted to investigate the effect of different training protocols on a large number of horses.