Heart Rate Variability Thresholds: Agreement with Established Approaches and Reproducibility in Trained Females and Males.

Abstract

To determine in trained females and males: i) the agreement between the gas exchange threshold (GET), lactate threshold 1 (LT1) and heart rate variability threshold 1 (HRVT1), as well as between the respiratory compensation point (RCP), lactate threshold 2 (LT2) and heart rate variability threshold 2 (HRVT2) and ii) the reproducibility of HRVT1 and HRVT2 during two-min incremental step protocols. Fifty-seven trained participants (24 females) completed a 2 min step incremental test to task failure. Nineteen participants (8 females) completed a second test to evaluate reproducibility. Gas exchange and ventilatory responses, blood lactate concentration, and RR time series were recorded to assess the oxygen consumption (V̇O2) and heart rate (HR) associated with the GET, RCP, LT1, LT2, HRVT1 and HRVT2. V̇O2-GET vs V̇O2-HRVT1 and HR-GET vs HR-HRVT1 were statistically different for females (29.5 ± 4.0 vs 34.6 ± 6.1 mL·kg-1·min-1; 154 ± 11 vs 166 ± 12 bpm) and for males (33.9 ± 4.2 vs 42.7 ± 4.6 mL·kg-1·min-1; 145 ± 11 vs 165 ± 9 bpm) (p < 0.001). V̇O2 and HR at HRVT1 were greater than at LT1 (p < 0.05). V̇O2-RCP vs V̇O2-HRVT2 and HR-RCP vs HR-HRVT2 were not statistically different for females (40.1 ± 4.7 vs 39.5 ± 6.7 mL·kg-1·min-1; 177 ± 9 vs 176 ± 9 bpm) and males (48.4 ± 5.4 vs 47.8 ± 4.8 mL·kg-1·min-1; 176 ± 8 vs 175 ± 9 bpm) (p > 0.05). V̇O2 and HR responses at LT2 were similar to HRVT2 (p > 0.05). Intraclass correlation (ICC) for V̇O2-HRVT1, HR-HRVT1, V̇O2-HRVT2, and HR-HRVT2 indicated good reproducibility when comparing the two different timepoints to standard methods. Whereas HRVT2 is a valid and reproducible estimate of the RCP/LT2, current approaches for HRVT1 estimation did not show good agreement with outcomes at GET and LT1.