Effect of a Lactate-Guided Conditioning Program on Fitness Markers in the Equine Athlete

Hypothesis: A lactate-guided conditioning program (CP) implementing twice-weekly short-duration high-intensity exercise bouts and once-weekly low-intensity longer-duration exercise bout effectively increases fitness in horses. Rationale: Blood lactate concentration ([LA]) is a measure of fitness in equine athletes. Most equine CPs are based on regular bouts of similar intensity exercise. We explore the effect of a CP that includes two higher-intensity bouts and one low-intensity bout/week. Methods: Six adult horses were subjected to a 12-week CP that consisted of twice-weekly exercise on an equine treadmill (6%-incline) for 25min at a velocity at which [LA] is 4.0mmol/L (VLA4.0) and once-weekly for 45min at a velocity at which [LA] is 2.5mmol/L (VLA2.5). VLA2.5 and VLA4.0 were determined by standardized-exercise-test (SET) before the CP and adjusted every 3wks. SETs started at 4.0m/s followed by 0.5m/s increments every 5min (6%-incline). Blood was collected for [LA], creatine kinase (CK), and aspartate aminotransferase (AST) before each speed increase and after termination of the SET, when [LA] ???4mmol/L. Repeated-measures ANOVA was used for analysis. Results: Heart rate, packed cell volume, and [LA] increased during all SETs. VLA2.5 and VLA4.0 increased throughout the CP, consistent with improved fitness (VLA2.5: 5.9??0.6 to 6.6??0.7m/s (p=0.034); VLA4.0: 6.4??0.6 to 7.4??0.6m/s (p=0.011)). There was a trend for the post-warm-up CK and AST to reduce over the CP (CK: 217??23 to 141??18; AST: 216??13 to 171??11). Principal Conclusions: This lactate-guided CP was effective at increasing fitness in these horses. Submaximal exercise can elevate CK and AST and these changes appear to be attenuated with conditioning