Sex differences in heart rate variability: a longitudinal study in international elite cross-country skiers
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Exercise-related sudden cardiac deaths (SCD) occur with a striking male predominance. A higher sympathetic tone in men has been suggested as risk factor for SCD. Elite athletes have the highest risk for exercise-related SCD. We aimed to analyze the autonomic nervous system of elite cross-country skiers from Norway, Russia and Switzerland in supine position and after orthostatic challenge in various training periods (TP).
Measurements of heart rate variability (HRV) were performed on a weekly basis over 1 year using an orthostatic challenge test with controlled breathing. Main outcome parameters were the high-frequency power in supine position (HFsupine) as marker of cardiac parasympathetic activity and the low-frequency/high-frequency power ratio after orthostatic challenge (LF/HFstand) as marker of cardiac sympathetic activation. Training intensity and duration were recorded daily and expressed as training strain. The training year was divided into three TPs. An average of weekly HRV measurements was calculated for each TP.
Female (n = 19, VO2max 62.0 ± 4.6 ml kg−1 min−1, age 25.8 ± 4.3 years) and male (n = 16, VO2max 74.3 ± 6.3 ml kg−1 min−1, age 24.4 ± 4.2 years) athletes were included. Training strain was comparable between sexes (all p > 0.05) and changed between TPs (all p < 0.05) while no HRV parameters changed over time. There were no sex differences in HFsupine while the LF/HFstand was significantly higher in male athletes in all TPs.
For a comparable amount of training, male athletes showed constantly higher markers of sympathetic activity after a provocation maneuver. This may explain part of the male predominance in sports-related SCD.
KeywordsAutonomic nervous system Heart rate variability Orthostatic test Athletes Endurance Training
Analysis of variance
Autonomic nervous system
Heart rate variability
Low-frequency/high-frequency power ratio
Mean of the R–R intervals
Preparation period 1
Preparation period 2
The square root of the mean squared differences of successive R–R intervals
Rate of perceived exertion
Standard deviation of all R–R intervals
Sudden cardiac death
In supine position
Standing after orthostatic challenge
We thank all study participants, their coaches and physicians for their contribution and Polar Electro Oy for providing us equipment and technical support.
Conflict of interest
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