Comparison of cardiac autonomic functions in elite endurance athletes and non-athletic healthy population: A cross-sectional study

Objectives: Long-term endurance training in elite endurance athletes (EEA) is known to affect the autonomic function by increasing the vagal tone which reflects in resting heart rate variability (HRV) but does this high resting vagal tone also affects the post-exercise heart rate recovery (HRR) remains unknown. Post-exercise HRR is used to prescribe and monitor athletic training. Hence, the aim was to determine HRR after maximal exercise among EEA and non-athletics healthy (NAH) populations and correlate it with resting HRV. Materials and Methods: Fifteen EEA and 15 NAH active male subjects of >18 years participated in this study. The resting HRV was measured with a continuous lead II electrocardiogram in the supine position for 10 min. The incremental exercise testing was done and post-exercise HRR data were collected. Results: In time domain analysis, average RR, median RR, root mean square of sequential deviations and percentage of successive interval difference larger than 50 ms were significantly higher, whereas the average heart rate was significantly lower in the EEA group. In the frequency domain analysis, low-frequency power–normalised units (LFnu), and low frequency (LF)/high frequency (HF) was significantly lower while high-frequency power––normalised units were significantly higher in the EEA group. The resting HRV indices did not correlate to HRR in both groups. Conclusion: The athletes have better adapted cardiac autonomic function as compared to the NAH group with higher resting vagal tone and better HRR. HRR did not correlate with resting HRV in either group, suggesting that parasympathetic activity causing a rapid decrease in heart rate post-exercise is independent of basal parasympathetic tone.