Effect of Lactate Minimum Speed-Guided Training on the Fluid, Electrolyte and Acid-Base Status of Horses

Abstract

The effect of lactate minimum speed (LMS)-guided training on horses' homeostasis is still unknown. Thus, this study aimed to evaluate the effect of an LMS-guided training program on the fluid, electrolyte and acid-base status of horses. Ten untrained Arabian horses were submitted to an LMS test on a treadmill before and after six weeks of training. The training intensity was 80% of the LMS in the first three sessions and 100% of the LMS in the other sessions. The venous blood was collected before (T-1) and after (T-2) training at rest, during and after the LMS test for lactate, pH, pCO₂, HCO₃^-, and electrolyte measurements. The LMS and strong ion difference (SID₄) were calculated. A mild increase in the mean values (p > 0.05) was observed at rest in T-2 in comparison with T-1 in the following variables: pH (from 7.436 ± 0.013 to 7.460 ± 0.012), pCO₂ (from 42.95 ± 1.58 to 45.06 ± 0.81 mmHg), HCO₃^- (from 27.01 ± 1.02 to 28.91 ± 0.86 mmol/L), and SID₄ (from 33.42 ± 1.45 to 35.06 ± 2.94 mmol/L). During T-2, these variables were more stable than during T-1. Despite the improvement in fitness, the LMS did not indicate a significant difference (from 5.40 ± 0.55 to 5.52 ± 0.20 m/s). The results confirmed that the LMS-guided training program had a positive impact on the horses' acid-base status, although some adaptations are still required to improve their fitness.

Keywords: athletic horse; conditioning program; endurance; exercise physiology.

Figure 1

Effort test scheme. The lactate minimum speed (LMS) test performed on a treadmill consisted of three phases: hyperlactatemia (Hlac) induction, which is a phase of short, high-intensity exercise to induce hyperlactatemia; active recovery to provide time for lactate transposition from muscle cells to the bloodstream; and incremental effort. Blood samples were collected at the end of hyperlactatemia induction and during the effort test to measure lactate for LMS determination. The LMS test produces a “U-shaped” lactate curve. The same protocol test was applied before and after the training period. The test lasted 57 min, and the horses traveled about 800 m at each speed. The time spent at each speed was variable. More details can be found in the Section 2.

Figure 2

Effect of six weeks of training on the response of blood lactate accumulation during the lactate minimum speed test (A). Before (T-1; blue circle) and after (T-2; red triangle) the training period. V = velocity; T = effort test; V × T = moment × test interaction. Second-order polynomial function curve fitted to lactate concentration as a function of speed in a representative animal (B). The running speeds were: 1.7, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, and 7.5 m/s. •, post-training lactate behavior.

Figure 3

Variation of blood pH (A), pCO₂ (B), HCO₃⁻ (bicarbonate) (C) and BE (base excess) (D) in horses. The measurements were performed at rest (M0), at the end of hyperlactatemia (M1), at early stages (M2, M3 and M4) and the end (M5) of the incremental effort, at the end of cool-down (M6), and 20 min after the end of the test (M7). T-1 (blue circle) and T-2 (red triangle) correspond to before and after the training period, respectively. M = moment; T = effort test; M × T = moment × test interaction. * Significant difference between tests 1 and 2.

Figure 4

Variation of SIG (A), SID₄ (B), A_tot (C), and PCV (D) in horses. A_tot, total concentration of nonvolatile buffers; PCV, packed cell volume; SID₄, strong ion difference; SIG, strong ion gap. The measurements were performed at rest (M0), at the end of hyperlactatemia (M1), at early stages (M2, M3 and M4) and the end (M5) of the incremental effort, at the end of cool-down (M6), and 20 min after the end of the test (M7). T-1 (blue circle) and T-2 (red triangle) correspond to before and after the training period, respectively. M = moment; T = effort test; M × T = moment × test interaction. * Significant difference between tests 1 and 2.