title: Reversal of runner's bradycardia with training overstress.
abstract: OBJECTIVE
  To elicit a criterion elevation (> 10%) in resting heart rate (HR) with training overstress, and subsequently test the hypothesis that such "reversed bradycardia" (RB) negatively affects running performance.
  
  
  METHODS
  Prospective before-and-after intervention with a comparison group.
  
  
  METHODS
  General community.
  
  
  METHODS
  21 healthy male marathon runners.
  
  
  METHODS
  Voluntary doubling of training miles on 14 consecutive days.
  
  
  METHODS
  Left ventricular (LV) function by echocardiography, HR, and plasma epinephrine (PE) at rest and during submaximal exercise, and 15 km road run performance.
  
  
  RESULTS
  Two days after the training overstress, 12 runners met the criterion (RB group), showing an average elevation in resting HR of 16% (range: 11 to 23%). The RB group also exhibited hyperkinetic LV shortening (p < 0.05), elevated exercise HR (p < 0.001), increased PE at rest and during exercise (p < 0.05), and reduced 15 km performance (p < 0.05). The other nine runners who maintained a stable resting HR during the intervention showed no significant outcome changes.
  
  
  CONCLUSIONS
  In addition to muscular overuse, heightened sympathetic drive likely contributed to the observed reversal of bradycardia. The development of this stress-related cardiac perturbation was associated with a decrement in running performance, confirming the hypothesis.
authors.affiliation: Division of Cardiology, William Beaumont Hospital, Royal Oak, Michigan, USA. penloom@jps.net
authors.forename: R H
authors.initials: RH
authors.lastname: Dressendorfer
authors.forename: A M
authors.initials: AM
authors.lastname: Hauser
authors.forename: G C
authors.initials: GC
authors.lastname: Timmis
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D000704:Analysis of Variance; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D008875:Middle Aged; D010806:Physical Education and Training / Q000379:methods*; D010807:Physical Endurance / Q000502:physiology*; D011446:Prospective Studies; D012420:Running / Q000502:physiology*; D016277:Ventricular Function, Left / Q000502:physiology
chemical_list: D015415:Biomarkers