Applicability of Dmax Method on Heart Rate Variability to Estimate the Lactate Thresholds in Male Runners

The purpose of this study was to evaluate the application of the Dmax method on heart rate variability (HRV) to estimate the lactate thresholds (LT), during a maximal incremental running test (MIRT).

Nineteen male runners performed two MIRTs, with the initial speed at 8 km·h^-1 and increments of 1 km·h^-1 every 3 minutes, until exhaustion. Measures of HRV and blood lactate concentrations were obtained, and lactate (LT₁ and LT₂) and HRV (HRVT_DMAX1 and HRVT_DMAX2) thresholds were identified. ANOVA with Scheffe's post hoc test, effect sizes (d), the bias ± 95% limits of agreement (LoA), standard error of the estimate (SEE), Pearson's (r), and intraclass correlation coefficient (ICC) were calculated to assess validity.

No significant differences were observed between HRVT_DMAX1 and LT₁ when expressed for speed (12.1 ± 1.4 km·h^-1 and 11.2 ± 2.1 km·h^-1; p=0.55; d = 0.45; r = 0.46; bias ± LoA = 0.8 ± 3.7 km·h^-1; SEE = 1.2 km·h^-1 (95% CI, 0.9-1.9)). Significant differences were observed between HRVT_DMAX2 and LT₂ when expressed for speed (12.0 ± 1.2 km·h^-1 and 14.1 ± 2.5 km·h^-1; p=0.00; d = 1.21; r = 0.48; bias ± LoA = -1.0 ± 1.8 km·h^-1; SEE = 1.1 km·h^-1 (95% CI, 0.8-1.6)), respectively. Reproducibility values were found for the LT₁ (ICC = 0.90; bias ± LoA = -0.7 ± 2.0 km·h^-1), LT₂ (ICC = 0.97; bias ± LoA = -0.1 ± 1.1 km·h^-1), HRVT_DMAX1 (ICC = 0.48; bias ± LoA = -0.2 ± 3.4 km·h^-1), and HRVT_DMAX2 (ICC = 0.30; bias ± LoA = 0.3 ± 3.5 km·h^-1).

The Dmax method applied over a HRV dataset allowed the identification of LT₁ that is close to aerobic threshold, during a MIRT.