title: Conversion from vagal to sympathetic predominance with strenuous training in high-performance world class athletes.
abstract: BACKGROUND
  Benefits of moderate endurance training include increases in parasympathetic activity and baroreflex sensitivity (BRS) and a relative decrease in sympathetic tone. However, the effect of very intensive training load on neural cardiovascular regulation is not known. We tested the hypothesis that strenuous endurance training, like in high-performance athletes, would enhance sympathetic activation and reduce vagal inhibition.
  
  
  RESULTS
  We studied the entire Italian junior national team of rowing (n=7) at increasing training loads up to 75% and 100% of maximum, the latter approximately 20 days before the Rowing World Championship. Autoregressive power spectral analysis was used to investigate RR interval and blood pressure (BP) variabilities. BRS was assessed by the sequences method. Increasing training load up to 75% of maximum was associated with a progressive resting bradycardia and increased indexes of cardiac vagal modulation and BRS. However, at 100% training load these effects were reversed, with increases in resting heart rate, diastolic BP, low-frequency RR interval, and BP variabilities and decreases in high-frequency RR variability and BRS. Three athletes later won medals in the World Championship.
  
  
  CONCLUSIONS
  This study indicates that very intensive endurance training shifted the cardiovascular autonomic modulation from a parasympathetic toward a sympathetic predominance. This finding should be interpreted within the context of the substantial role played by the sympathetic nervous system in increasing cardiovascular performance at peak training. Whether the altered BP and autonomic function shown in this study might be in time hazardous to human cardiovascular system remains to be established.
authors.affiliation: Dipartimento di Medicina Interna-Centro di Riabilitazione Cardiologica S. Raffaele, Università di Roma Tor Vergata, Roma, Italy. iellamo@med.uniroma2.it
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Iellamo
authors.forename: Jacopo M
authors.initials: JM
authors.lastname: Legramante
authors.forename: Fabio
authors.initials: F
authors.lastname: Pigozzi
authors.forename: Antonio
authors.initials: A
authors.lastname: Spataro
authors.forename: Guido
authors.initials: G
authors.lastname: Norbiato
authors.forename: Daniela
authors.initials: D
authors.lastname: Lucini
authors.forename: Massimo
authors.initials: M
authors.lastname: Pagani
mesh_terms: D000328:Adult; D017704:Baroreflex; D001794:Blood Pressure; D002318:Cardiovascular Diseases / Q000209:etiology; D004562:Electrocardiography; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D008297:Male; D010807:Physical Endurance / Q000502:physiology*; D012307:Risk Factors; D013177:Sports / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology*