An examination of the physiological responses at the critical heart rate

The purposes of this study were to: (1) apply the critical power (CP) model to heart rate (HR) data to propose a HR based analog of the CP test called the critical heart rate (CHR) test; (2) compare the CHR to HR values at CP (CPHR), ventilatory threshold (VT1HR), and respiratory compensation point (VT2HR); and (3) examine the V˙O 2, RPE, EMG, and MMG responses to 1-hr continuous rides at the CHR, CHR+5 bpm, and CHR-5 bpm. Ten women performed an incremental test to exhaustion to determine V˙O2 peak, VT1, VT2, VT1HR, and VT2HR The subjects also performed four exhaustive workbouts at different power outputs (P) to determine CP and CHR. For each P, the total number of heart beats (HBlim) was calculated as the product of the average 5-second HR (bpm) and total time to exhaustion (T lim in min). The HBlim and total work (Wlim in kgm) were plotted as a function of the Tlim at each P and the slope coefficients of the regression lines between HBlim or Wlim and Tlim were defined as the CHR and CP, respectively. The mathematical model used for the determination of CP was applicable to HR measurements to estimate the CHR. A one-way repeated measure ANOVA indicated that CHR (175 ± 11 bpm, 92.6 ± 2.8% HRmax) was not significantly different from VT2HR (174 ± 10 bpm, 92.3 ± 2.3% HR max), but was higher (p\u3c0.05) than the CPHR (156 ± 11 bpm, 83. 4 ± 4.0% HRmax) and VT1HR (154 ± 12 bpm, 81.2 ± 4.0% HRmax). The workbouts at CHR (37.2 ± 20.3min), CHR+5 (23.9 ± 16.6min), and CHR-5 (51.6 ± 16.8min) were fatiguing tasks because RPE increased, even though P and V˙O 2 decreased. During the continuous workbouts at constant HR values, the EMG amplitude and mean power frequency (MPF) responses did not identify fatigue. The RPE, MMG amplitude, and MMG MPF, however, resulted in patterns of responses that were consistent with the increase in fatigue during a constant HR workbout