title: Insomnia symptoms and cardiorespiratory fitness in healthy individuals: the Nord-Trøndelag Health Study (HUNT).
abstract: OBJECTIVE
  Previous studies have found an inverse association between insomnia and self-reported physical activity, but it is not clear whether insomnia is associated with cardiorespiratory fitness. Our aim was to investigate different insomnia symptoms in relation to the gold standard measure of cardiorespiratory fitness, i.e., peak oxygen uptake (VO(2peak)).
  
  
  METHODS
  Cross-sectional population study.
  
  
  METHODS
  Nord-Trøndelag County, Norway.
  
  
  METHODS
  The group comprised 3,489 men and women who were free from cardiovascular or pulmonary diseases, cancer, and sarcoidosis and who did not use antihypertensive medication. They were included in the fully adjusted model when assessing all insomnia symptoms simultaneously.
  
  
  METHODS
  N/A.
  
  
  RESULTS
  For insomnia, the participants reported how often they had experienced sleep problems during the past 3 months, including difficulties falling asleep at night, repeated awakenings during the night, early awakenings without being able to go back to sleep, and daytime sleepiness. Response options were "never/almost never," "sometimes" or "several times a wk." To measure cardiorespiratory fitness, the participants were asked to walk or run on a treadmill with increasing speed and/or incline until exhaustion, and VO(2peak) was recorded. We found a modest inverse and graded association of the insomnia symptoms with VO(2peak). The association was independent of self-reported physical activity and was apparent for all insomnia symptoms except for early awakenings. We found a dose-response relation for a cumulative combination of insomnia symptoms and VO(2peak) for experiencing zero, one to two, or three to four symptoms (P for trend < 0.001).
  
  
  CONCLUSIONS
  We found a modest inverse association of insomnia with VO(2peak) independent of the conventional cardiovascular risk factors and self-reported physical activity.
authors.affiliation: Department of Public Health and General Practice, Norwegian University of Science and Technology, Trondheim, Norway. linn.b.strand@ntnu.no
authors.forename: Linn B
authors.initials: LB
authors.lastname: Strand
authors.forename: Lars E
authors.initials: LE
authors.lastname: Laugsand
authors.forename: Ulrik
authors.initials: U
authors.lastname: Wisløff
authors.forename: Bjarne M
authors.initials: BM
authors.lastname: Nes
authors.forename: Lars
authors.initials: L
authors.lastname: Vatten
authors.forename: Imre
authors.initials: I
authors.lastname: Janszky
mesh_terms: D002320:Cardiovascular Physiological Phenomena; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology; D005080:Exercise Test / Q000379:methods; D005260:Female; D006304:Health Status; D006306:Health Surveys / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D010101:Oxygen Consumption / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology*; D012143:Respiratory Physiological Phenomena; D007319:Sleep Initiation and Maintenance Disorders / Q000453:epidemiology* / Q000503:physiopathology*; D011795:Surveys and Questionnaires