title: Relation between heart rate variability and training load in middle-distance runners.
abstract: OBJECTIVE
  Monitoring physical performance is of major importance in competitive sports. Indices commonly used, like resting heart rate, VO2max, and hormones, cannot be easily used because of difficulties in routine use, of variations too small to be reliable, or of technical challenges in acquiring the data.
  
  
  METHODS
  We chose to assess autonomic nervous system activity using heart rate variability in seven middle-distance runners, aged 24.6 +/- 4.8 yr, during their usual training cycle composed of 3 wk of heavy training periods, followed by a relative resting week. The electrocardiogram was recorded overnight twice a week and temporal and frequency indices of heart rate variability, using Fourier and Wavelet transforms, were calculated. Daily training loads and fatigue sensations were estimated with a questionnaire. Similar recordings were performed in a sedentary control group.
  
  
  RESULTS
  The results demonstrated a significant and progressive decrease in parasympathetic indices of up to -41% (P < 0.05) during the 3 wk of heavy training, followed by a significant increase during the relative resting week of up to +46% (P < 0.05). The indices of sympathetic activity followed the opposite trend, first up to +31% and then -24% (P < 0.05), respectively. The percentage increasing mean nocturnal heart rate variation remained below 12% (P < 0.05). There was no significant variation in the control group.
  
  
  CONCLUSIONS
  This study confirmed that heavy training shifted the cardiac autonomic balance toward a predominance of the sympathetic over the parasympathetic drive. When recorded during the night, heart rate variability appeared to be a better tool than resting heart rate to evaluate cumulated physical fatigue, as it magnified the induced changes in autonomic nervous system activity. These results could be of interest for optimizing individual training profiles.
authors.affiliation: Laboratoire de Physiologie, Université de Saint-Etienne, France.
authors.forename: V
authors.initials: V
authors.lastname: Pichot
authors.forename: F
authors.initials: F
authors.lastname: Roche
authors.forename: J M
authors.initials: JM
authors.lastname: Gaspoz
authors.forename: F
authors.initials: F
authors.lastname: Enjolras
authors.forename: A
authors.initials: A
authors.lastname: Antoniadis
authors.forename: P
authors.initials: P
authors.lastname: Minini
authors.forename: F
authors.initials: F
authors.lastname: Costes
authors.forename: T
authors.initials: T
authors.lastname: Busso
authors.forename: J R
authors.initials: JR
authors.lastname: Lacour
authors.forename: J C
authors.initials: JC
authors.lastname: Barthélémy
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology; D016022:Case-Control Studies; D004562:Electrocardiography; D017079:Exercise Tolerance / Q000502:physiology*; D005221:Fatigue; D005583:Fourier Analysis; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D011446:Prospective Studies; D012420:Running; D011795:Surveys and Questionnaires