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

Effect of a Lactate-Guided Conditioning Program on Fitness Markers in the Equine Athlete A.L. Fisher, H.M. Greene MS, R.J. Talmadge PhD, Y.S. Nout-Lomas DVM, PhD 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. Here we explore the effect of a CP that includes two shorter higher-intensity bouts and one longer 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 incremental-step standardized-exercise-test (SET) before the CP and adjusted every 3wks (total 4 SETs). SETs started at 4.0m/s and were 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 at 2, 4, and 24hrs after termination of the SET, when [LA] reached ≥4mmol/L. Repeated-measures ANOVA was used for analysis. Results: Over the course of the SETs horses showed an increase in heart rate, packed cell volume, and [LA]. In all horses VLA2.5 and VLA4.0 increased throughout the 12-week CP, consistent with improved fitness. VLA2.5 increased from 5.9±0.6 to 6.6±0.7m/s (p=0.034) and VLA4.0 from 6.4±0.6 to 7.4±0.6m/s (p=0.011). For each SET there was a trend for CK to increase 2hrs post-exercise, however, this was not significant. There was a trend for the post-warm-up CK and AST to reduce over the 12-week 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.