title: Sex differences in heart rate variability: a longitudinal study in international elite cross-country skiers.
abstract: OBJECTIVE
  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).
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Division of Preventive Cardiology and Sports Medicine, University Clinic for Cardiology, Inselspital University Hospital and University of Bern, 3010, Bern, Switzerland.
authors.forename: Daniela
authors.initials: D
authors.lastname: Schäfer
authors.affiliation: Section of Vascular Investigations, Oslo University Hospital, Bjorknes College, Oslo, Norway.
authors.forename: Gard Filip
authors.initials: GF
authors.lastname: Gjerdalen
authors.affiliation: Diakonhjemmet Sykehus, Oslo, Norway.
authors.forename: Erik Ekker
authors.initials: EE
authors.lastname: Solberg
authors.affiliation: Moscow Department of Public Health, Moscow Research and Practical Center of Medical Rehabilitation, Restorative and Sports Medicine, Moscow, Russia.
authors.forename: Maria
authors.initials: M
authors.lastname: Khokhlova
authors.affiliation: Moscow Department of Public Health, Moscow Research and Practical Center of Medical Rehabilitation, Restorative and Sports Medicine, Moscow, Russia.
authors.forename: Victoria
authors.initials: V
authors.lastname: Badtieva
authors.affiliation: Division of Preventive Cardiology and Sports Medicine, University Clinic for Cardiology, Inselspital University Hospital and University of Bern, 3010, Bern, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Herzig
authors.affiliation: Division of Preventive Cardiology and Sports Medicine, University Clinic for Cardiology, Inselspital University Hospital and University of Bern, 3010, Bern, Switzerland.
authors.forename: Lukas Daniel
authors.initials: LD
authors.lastname: Trachsel
authors.affiliation: Swiss Olympic Medical Base, St. Gallen, Switzerland.
authors.forename: Patrik
authors.initials: P
authors.lastname: Noack
authors.affiliation: Polar Electro Oy, Kempele, Finland.
authors.forename: Laura
authors.initials: L
authors.lastname: Karavirta
authors.affiliation: Division of Preventive Cardiology and Sports Medicine, University Clinic for Cardiology, Inselspital University Hospital and University of Bern, 3010, Bern, Switzerland.
authors.forename: Prisca
authors.initials: P
authors.lastname: Eser
authors.affiliation: Division of Preventive Cardiology and Sports Medicine, University Clinic for Cardiology, Inselspital University Hospital and University of Bern, 3010, Bern, Switzerland.
authors.forename: Hugo
authors.initials: H
authors.lastname: Saner
authors.affiliation: Division of Preventive Cardiology and Sports Medicine, University Clinic for Cardiology, Inselspital University Hospital and University of Bern, 3010, Bern, Switzerland. matthias.wilhelm@insel.ch.
authors.forename: Matthias
authors.initials: M
authors.lastname: Wilhelm
mesh_terms: D000328:Adult; D056352:Athletes; D001341:Autonomic Nervous System / Q000502:physiology; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D012737:Sex Factors; D012865:Skiing / Q000502:physiology*
keywords: Athletes; Autonomic nervous system; Endurance; Heart rate variability; Orthostatic test; Training