title: Temporal dynamics of the circadian heart rate following low and high volume exercise training in sedentary male subjects.
abstract: OBJECTIVE
  Increased risk of arrhythmic events occurs at certain times during the circadian cycle with the highest risk being in the second and fourth quarter of the day. Exercise improves treatment outcome in individuals with cardiovascular disease. How different exercise protocols affect the circadian rhythm and the associated decrease in adverse cardiovascular risk over the circadian cycle has not been shown.
  
  
  METHODS
  Fifty sedentary male participants were randomized into an 8-week high volume and moderate volume training and a control group. Heart rate was recorded using Polar Electronics and investigated with Cosinor analysis and by Poincaré plot derived features of SD1, SD2 and the complex correlation measure (CCM) at 1-h intervals over the 24-h period.
  
  
  RESULTS
  Moderate exercise significantly increased vagal modulation and the temporal dynamics of the heart rate in the second quarter of the circadian cycle (p = 0.004 and p = 0.007 respectively). High volume exercise had a similar effect on vagal output (p = 0.003) and temporal dynamics (p = 0.003). Cosinor analysis confirms that the circadian heart rate displays a shift in the acrophage following moderate and high volume exercise from before waking (1st quarter) to after waking (2nd quarter of day).
  
  
  CONCLUSIONS
  Our results suggest that exercise shifts vagal influence and increases temporal dynamics of the heart rate to the 2nd quarter of the day and suggest that this may be the underlying physiological change leading to a decrease in adverse arrhythmic events during this otherwise high-risk period.
authors.affiliation: Australian School of Advanced Medicine, Macquarie University, Sydney, Australia. hjelinek@csu.edu.au.|Centre for Research in Complex Systems and School of Community Health, Charles Sturt University, Albury, Australia. hjelinek@csu.edu.au.
authors.forename: Herbert F
authors.initials: HF
authors.lastname: Jelinek
authors.affiliation: Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia.
authors.forename: C
authors.initials: C
authors.lastname: Karmakar
authors.affiliation: Department of Exercise and Medical Physiology, Verve Research, Oulu, Finland.
authors.forename: A M
authors.initials: AM
authors.lastname: Kiviniemi
authors.affiliation: Department of Exercise and Medical Physiology, Verve Research, Oulu, Finland.
authors.forename: A J
authors.initials: AJ
authors.lastname: Hautala
authors.affiliation: Department of Exercise and Medical Physiology, Verve Research, Oulu, Finland.
authors.forename: M P
authors.initials: MP
authors.lastname: Tulppo
authors.affiliation: Institute of Clinical Medicine, University of Oulu, Oulu, Finland.
authors.forename: T H
authors.initials: TH
authors.lastname: Mäkikallio
authors.affiliation: Institute of Clinical Medicine, University of Oulu, Oulu, Finland.
authors.forename: H V
authors.initials: HV
authors.lastname: Huikuri
authors.affiliation: Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia.|Department of Biomedical Engineering, Khalifa University, Abu Dhabi, UAE.
authors.forename: A H
authors.initials: AH
authors.lastname: Khandoker
authors.affiliation: Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Palaniswami
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D015444:Exercise; D006321:Heart / Q000502:physiology; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D057185:Sedentary Behavior; D014630:Vagus Nerve / Q000502:physiology
keywords: Circadian; Cosinor modeling; Exercise; Heart rate variability