Influence of high-frequency bandwidth on heart rate variability analysis during physical exercise

Heart rate variability (HRV) analysis of beat-to-beat RR interval data was performed in 11 asymptomatic young male subjects during a progressive bicycle exercise test. RR interval data (Polar S810) and breath-by-breath respiratory data (rate, minute ventilation and oxygen uptake) (Oxycon Pro) were simultaneously recorded throughout exercise. ‘Ventilation per second’ was defined as V˙Esec, the change (from the previous epoch) in ventilatory volume per second. Power spectral analysis quantified power distribution of RR data within the bandwidths 0.04–0.15 Hz (LF), 0.15–0.4 Hz (HF0.4), 0.15–1.0 Hz (HF1.0), 0.15–2.0 Hz (HF2.0) and 0.15 to V˙Esec (HFV˙Esec). Absolute powers within the LF and all HF bandwidths decreased continuously throughout exercise (exercise intensity range 18 ± 1 to 81 ± 1% V˙O2max). At mild-to-moderate exercise intensities (18 ± 1 to 55 ± 1% V˙O2max) there were no significant differences between the LF/HF ratios calculated using each of the band-limited HF components. However, at moderate-to-high intensities (64 ± 1 to 81 ± 1% V˙O2max) there was a significant difference between LF/HF0.4 and the LF/HF ratios calculated using each of the broader HF bandwidths (P < 0.05). In addition, LF/HF1.0 was significantly greater than both LF/HF2.0 and LF/HFV˙Esec at the highest exercise intensity (81 ± 1% V˙O2max). These results suggest that the upper HF bandwidth limit should be extended to dynamically match V˙Esec when quantifying HRV during moderate-to-high intensity exercise. When the simultaneous recording of respiratory data is not practical, an HF bandwidth upper limit of 2.0 Hz would be an appropriate choice.