The purpose of this study was to implement a new method for assessing the ventilatory thresholds from heart rate variability (HRV) analysis. ECG, V·O2, V·CO2, and V·E were collected from eleven well-trained subjects during an incremental exhaustive test performed on a cycle ergometer. The "Short-Term Fourier Transform" analysis was applied to RR time series to compute the high frequency HRV energy (HF, frequency range: 0.15 - 2 Hz) and HF frequency peak (fHF) vs. power stages. For all subjects, visual examination of ventilatory equivalents, fHF, and instantaneous HF energy multiplied by fHF (HF · fHF) showed two nonlinear increases. The first nonlinear increase corresponded to the first ventilatory threshold (VT1) and was associated with the first HF threshold (TRSA1 from fHF and HFT1 from HF · fHF detection). The second nonlinear increase represented the second ventilatory threshold (VT2) and was associated with the second HF threshold (TRSA2 from fHF and HFT2 from HF · fHF detection). HFT1 , TRSA1, HFT2, and TRSA2 were, respectively, not significantly different from VT1 (VT1 = 219 ± 45 vs. HFT1 = 220 ± 48 W, p = 0.975; VT1 vs. TRSA1 = 213 ± 56 W, p = 0.662) and VT2 (VT2 = 293 ± 45 vs. HFT2 = 294 ± - 48 W, p = 0.956; vs. TRSA2 = 300 ± 58 W, p = 0.445). In addition, when expressed as a function of power, HFT1, TRSA1, HFT2, and TRSA2 were respectively correlated with VT1 (with HFT1 r² = 0.94, p < 0.001; with TRSA1 r² = 0.48, p < 0.05) and VT2 (with HFT2 r² = 0.97, p < 0.001; with TRSA2 r² = 0.79, p < 0.001). This study confirms that ventilatory thresholds can be determined from RR time series using HRV time-frequency analysis in healthy well-trained subjects. In addition it shows that HF · fHF provides a more reliable and accurate index than fHF alone for this assessment.
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