The association of various speed indices to training responses in Thoroughbred flat racehorses measured with a global positioning and heart rate monitoring system

P>Reasons for performing study: Fitness assessment can be challenging. The use of global positioning systems (GPS) with heart rate (HR) monitors has been promising; however, evaluation of speed parameters during training has not been reported. Objectives: To evaluate speed indices during training in Thoroughbreds using a GPS-HR monitor. Methods: Thoroughbreds (n = 102) were assessed during training with data collected each work day (WD; sprinting). Speed indices evaluated included maximal velocity (V-max), duration at V-max (V-maxt), acceleration rate (m/s2 ) from 800 m to V-max (Acc800-V-max), the distance (m) 6 (V-maxD6) and 12 (V-maxD12) s before (acceleration [a]) and after (deceleration [d]) V-max and the deceleration rate from V-max to the finish (V-maxDFd). Blood for plasma lactate ([LA]) and creatine kinase ([CK]) measurements were taken before (T-0), 5 mins (T-1) and 6 h after exercise (T-2). WD accumulation, jockey, gallop condition, horse gender, age, total distance covered (DistT), maximum HR (HRmax), velocity at 200 beats/min (V-200) and velocity at maximum HR (VHRmax) for each WD were evaluated for associations with [LA], [CK], speed indices and racing performance. Data were analysed by repeated measures ANOVA with P < 0.05 significant. Results: No speed parameter clearly changed with training. Gallop condition affected V-max, V-maxt and all distances covered with V-max and distances increasing and V-maxt decreasing as gallop surface became firmer. Jockey influenced V-max, V-maxD6a and all decelerations, while DistT was inversely associated with Acc800-V-max, HRmax and V-200 and positively associated with V-max, all accelerations and decelerations. [LA] at T-1 was positively associated with DistT and V-maxDFd. Conclusions: Speed parameters did not change with training but were affected by jockey, gallop condition and exercise distance. This information may help to modify training to maximise fitness, minimise injury and choose distances best suited for individuals.