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

Purpose: 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 2-min incremental step protocols. Methods: Fifty-seven trained participants (24 females) completed a 2-min step incremental test to task failure. Nineteen participants (eight 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 (VO2) and heart rate (HR) associated with the GET, RCP, LT1, LT2, HRVT1, and HRVT2. Results: VO2-GET versus VO2-HRVT1 and HR-GET versus HR-HRVT1 were statistically different for females (29.5 +/- 4.0 vs 34.6 +/- 6.1 mL<middle dot>kg(-1)<middle dot>min(-1); 154 +/- 11 vs 166 +/- 12 bpm) and for males (33.9 +/- 4.2 vs 42.7 +/- 4.6 mL<middle dot>kg(-1)<middle dot>min(-1); 145 +/- 11 vs 165 +/- 9 bpm; P < 0.001). VO2 and HR at HRVT1 were greater than at LT1 (P < 0.05). VO2-RCP versus VO2-HRVT2 and HR-RCP versus HR-HRVT2 were not statistically different for females (40.1 +/- 4.7 vs 39.5 +/- 6.7 mL<middle dot>kg(-1)<middle dot>min(-1); 177 +/- 9 vs 176 +/- 9 bpm) and males (48.4 +/- 5.4 vs 47.8 +/- 4.8 mL<middle dot>kg(-1)<middle dot>min(-1); 176 +/- 8 vs 175 +/- 9 bpm; P > 0.05). VO2 and HR responses at LT2 were similar to HRVT2 (P > 0.05). Intraclass correlation coefficient for VO2-HRVT1, HR-HRVT1, VO2-HRVT2, and HR-HRVT2 indicated good reproducibility when comparing the two different time points to standard methods. Conclusions: 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.