Power spectrum of heart rate variability in exercising humans: The effect of exercise intensity

Power spectral analysis of heart rate variability (HRV) has been estimated by means of a Fourier transform method at rest in seven healthy men and three women, during a 30‐minutes steady state cycle exercise test at 40%, 50%, 60%, 70% and 80% respectively, of maximal heart rate reserve (MHRR) defined as (HRmax ‐ HRrest). Total power (PT) of HRV was divided into three separate components (PHf, Plf, and Pvlf). All four indices for HRV decreased significantly with increasing exercise intensity. The fractional Pvlf (%VLF), VLF/LF ratio, and VLF/HF ratio increased significantly with increasing exercise intensity. On the contrary, %LF and %HF decreased significantly with increasing exercise intensity. The following conclusions were made: (1) the contribution of parasympathetic activity to the power spectrum of HRV decreases with exercise intensity; (2) the change in %VLF, VLF/LF ratio, and VLF/HF ratio respectively, can be used as indices of change in sympathovagal balance during exercise; (3) the change in the LF/HF ratio cannot be used during exercise as an index of change in sympathovagal balance, since a change in vagal activity effects predominantly both numerator and denominator of the LF/HF ratio.