title: Caffeine delays autonomic recovery following acute exercise.
abstract: BACKGROUND
  Impaired autonomic recovery of heart rate (HR) following exercise is associated with an increased risk of sudden death. Caffeine, a potent stimulator of catecholamine release, has been shown to augment blood pressure (BP) and sympathetic nerve activity; however, whether caffeine alters autonomic function after a bout of exercise bout remains unclear.
  
  
  METHODS
  In a randomized, crossover study, 18 healthy individuals (26 ± 1 years; 23.9 ± 0.8 kg·m(-2)) ingested caffeine (400 mg) or placebo pills, followed by a maximal treadmill test to exhaustion. Autonomic function and ventricular depolarization/repolarization were determined using heart rate variability (HRV) and corrected QT interval (QTc), respectively, at baseline, 5, 15, and 30 minutes post-exercise.
  
  
  RESULTS
  Maximal HR (HRmax) was greater with caffeine (192 ± 2 vs. 190 ± 2 beat·min(-1), p < 0.05). During recovery, HR, mean arterial pressure (MAP), and diastolic blood pressure (DBP) remained elevated with caffeine (p < 0.05). Natural log transformation of low-to-high frequency ratio (LnLF/LnHF) of HRV was increased compared with baseline at all time points in both trials (p < 0.05), with less of an increase during 5 and 15 minutes post-exercise in the caffeine trial (p < 0.05). QTc increased from baseline at all time points in both trials, with greater increases in the caffeine trial (p < 0.05).
  
  
  CONCLUSIONS
  Caffeine ingestion disrupts post-exercise autonomic recovery because of increased sympathetic nerve activity. The prolonged sympathetic recovery time could subsequently hinder baroreflex function during recovery and disrupt the stability of autonomic function, potentiating a pro-arrhythmogenic state in young adults.
authors.affiliation: Department of Kinesiology and Nutrition, The University of Illinois at Chicago, IL, USA bunsawa2@uic.edu.
authors.forename: Kanokwan
authors.initials: K
authors.lastname: Bunsawat
authors.affiliation: Department of Kinesiology and Nutrition, The University of Illinois at Chicago, IL, USA.
authors.forename: Daniel W
authors.initials: DW
authors.lastname: White
authors.affiliation: Department of Kinesiology and Nutrition, The University of Illinois at Chicago, IL, USA.
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Kappus
authors.affiliation: Department of Kinesiology and Nutrition, The University of Illinois at Chicago, IL, USA.
authors.forename: Tracy
authors.initials: T
authors.lastname: Baynard
mesh_terms: D000328:Adult; D062186:Arterial Pressure / Q000187:drug effects*; D001341:Autonomic Nervous System / Q000187:drug effects* / Q000502:physiology; D017704:Baroreflex / Q000187:drug effects*; D002110:Caffeine / Q000008:administration & dosage*; D002641:Chicago; D018592:Cross-Over Studies; D004311:Double-Blind Method; D015444:Exercise; D005260:Female; D064368:Healthy Volunteers; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D008297:Male; D020127:Recovery of Function; D013997:Time Factors
chemical_list: D002110:Caffeine
keywords: Caffeine; autonomic function; exercise recovery