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

Introduction . 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). Methods . 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 (LT 1 and LT 2 ) 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. Results . No significant differences were observed between HRVT DMAX1 and LT 1 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 LT 2 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 LT 1 (ICC = 0.90; bias ± LoA = −0.7 ± 2.0 km·h −1 ), LT 2 (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 ). Conclusions . The Dmax method applied over a HRV dataset allowed the identification of LT 1 that is close to aerobic threshold, during a MIRT.