Maximal Lactate Steady State Prediction Using Two DMAX Methods in Horses Subjected to Treadmill-Graded Exercise Test

Maximal lactate steady state (MLSS) and its predictive thresholds, including the lactate threshold (LT), are widely used to estimate endurance capacity, prescribe training, and assess the effects of training. The human literature identified approximately twenty-five methods to predict the MLSS. This communication compares the concordance between the two D_MAX methods and the MLSS. Under laboratory conditions, ten teaching horses underwent a submaximal graded exercise test (GXT) on a treadmill to obtain their lactate-velocity curves (LVC). They performed three to five 30-min continuous running sessions to determine the MLSS. The traditional D_MAX method was determined using the maximal distance from LVC to the line formed by its endpoints. A new calculated D_MAX method (D_MAXC) involved mathematically determining the point that results in the maximum distance from a curve connecting the start to the endpoint of the LVC. The agreement among the velocities corresponding to the D_MAX (V_MAX), D_MAXC (V_MAXC), and the MLSS (V_MLSS) was established using a Bland-Altman plot and ordinary least products (OLP) analysis. The average lactatemia at V_MLSS, V_MAX, and V_MAXC was 1.50 ± 0.36 mM, 2.02 ± 0.66 mM, and 1.92 ± 0.65 mM, with respective speeds of 5.42 ± 0.57 m/s, 6.42 ± 0.71 m/s, and 6.35 ± 0.66 m/s. The mean difference between V_MAX-V_MLSS and V_MAXC-V_MLSS was -1.01 ± 0.61 and -0.93 ± 0.67 m/s, respectively. V_MAX and V_MAXC did not show constant and proportional biases compared to V_MLSS. In the GXT protocol used in this current study, D_MAX approaches appear to be accurate and reliable methods for lactate threshold determination and estimating MLSS in teaching horses.