Decrease of heart rate variability during exercise: An index of cardiorespiratory fitness

Fig 1. Example of RR series cleaning. Measured RR interval during a maximal graded effort test (effort starts at time = 0). The points removed by our cleaning procedure are indicated in red.

Fig 2. Example of RR series detrending. Measured RR interval during a maximal graded effort test, its estimation by a first order differential equation and the resulting detrended RR values obtained by subtracting the model estimate to the real data.

Fig 3. Different representations of HRV during effort. SDRR of the detrended RR time series recorded during a graded effort test as a function of: A) the mean heart rate (HR) during the interval, B) the work load during the exercise test and C) the mean work intensity. The color of the points indicates the SDRR was calculating on RR before (pre-effort), during (effort), or after (recovery) the effort. The solid red line corresponds to the regression estimate obtained on the entire set of SDRR values using model 1, 2 and 3 of Eq 2 in A, B, and C, respectively, and dashed red lines are the regression estimate obtained on SDRR values during effort only (i.e. excluding pre-effort and recovery periods) using model 1, 2 and 3 of Eq 2 in A, B, and C, respectively.

Fig 4. Results of the sensitivity analysis. Pearson correlation coefficient and associated p value (p < 0.05 or p > = 0.05) found between HRV decay constant and VO2max as a function of the windows size ω when using a 0th (p = 0) order polynomial detrending.