title: Risk of arrhythmias in 52 755 long-distance cross-country skiers: a cohort study.
abstract: OBJECTIVE
  We aimed to investigate the association of number of completed races and finishing time with risk of arrhythmias among participants of Vasaloppet, a 90 km cross-country skiing event.
  
  
  RESULTS
  All the participants without cardiovascular disease who completed Vasaloppet during 1989-98 were followed through national registries until December 2005. Primary outcome was hospitalization for any arrhythmia and secondary outcomes were atrial fibrillation/flutter (AF), bradyarrhythmias, other supraventricular tachycardias (SVT), and ventricular tachycardia/ventricular fibrillation/cardiac arrest (VT/VF/CA). Among 52 755 participants, 919 experienced arrhythmia during follow-up. Adjusting for age, education, and occupational status, those who completed the highest number of races during the period had higher risk of any arrhythmias [hazard ratio (HR)1.30; 95% CI 1.08-1.58; for ≥5 vs. 1 completed race], AF (HR 1.29; 95% CI 1.04-1.61), and bradyarrhythmias (HR 2.10; 95% CI 1.28-3.47). Those who had the fastest relative finishing time also had higher risk of any arrhythmias (HR 1.30; 95% CI 1.04-1.62; for 100-160% vs. >240% of winning time), AF (1.20; 95% CI 0.93-1.55), and bradyarrhythmias (HR 1.85; 95% CI 0.97-3.54). SVT or VT/VF/CA was not associated with finishing time or number of completed races.
  
  
  CONCLUSIONS
  Among male participants of a 90 km cross-country skiing event, a faster finishing time and a high number of completed races were associated with higher risk of arrhythmias. This was mainly driven by a higher incidence of AF and bradyarrhythmias. No association with SVT or VT/VF/CA was found.
authors.affiliation: Department of Medical Sciences, Uppsala University Hospital, Entrance 40, 5th floor, SE-751 85 Uppsala, Sweden.
authors.forename: Kasper
authors.initials: K
authors.lastname: Andersen
authors.forename: Bahman
authors.initials: B
authors.lastname: Farahmand
authors.forename: Anders
authors.initials: A
authors.lastname: Ahlbom
authors.forename: Claes
authors.initials: C
authors.lastname: Held
authors.forename: Sverker
authors.initials: S
authors.lastname: Ljunghall
authors.forename: Karl
authors.initials: K
authors.lastname: Michaëlsson
authors.forename: Johan
authors.initials: J
authors.lastname: Sundström
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001145:Arrhythmias, Cardiac / Q000453:epidemiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D058687:Out-of-Hospital Cardiac Arrest / Q000453:epidemiology; D012307:Risk Factors; D012865:Skiing / Q000502:physiology* / Q000706:statistics & numerical data; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: Arrhythmia; Atrial fibrillation; Bradycardia; Cross-country skiing; Exercise training