Sex-specific reaction of the cardiac autonomic ­nervous system to different training phases in Swiss elite runners

Abstract

Background: Heart rate variability (HRV) as a measure of the cardiac autonomic nervous system activity (CANA) has the potential to tailor endurance training and may contribute to the prevention of overtraining. We aimed to investigate whether there are sex differences and sex-specific reactions of the CANA to different training periods (TPs) in Swiss elite runners. Methods: Two HRV measurements (each 5 minutes supine and 5 minutes standing) per athlete were performed, the first during preparation period (PP) and the second during competition period (CP). Main outcome parameters were the square root of the mean squared differences of successive R-R intervals in supine position (RMSSDsupine) as a time-domain marker of parasympathetic activity and the low frequency/high frequency power ratio after orthostatic challenge (LF/HFstand) as a frequency-domain marker of the sympatho-vagal balance. Average total number of training sessions per week (TSPW) as well as number of high-intensity and low-intensity TSPW was recorded. Results: Fifteen female (23.5±4.2 years) and 22 male (21.8±3.2 years) elite runners were included. Females reported a higher number of low-intensity TSPW in PP while there were no sex differences in any other training parameters. Females showed a higher RMSSDsupine and a lower LF/HFstand compared to their male counterparts in both training periods. Males showed a higher LF/HFstand in CP compared to PP while LF/HFstand remained unchanged in females in both periods. Conclusion: Male runners showed a shift towards higher markers of sympathetic activity in CP compared to PP while these markers did not change between TPs in female runners. Compared to males, females had higher markers of parasympathetic activity and lower markers of sympathetic activity in all TPs.