title: Autonomic adaptations to intensive and overload training periods: a laboratory study.
abstract: OBJECTIVE
  Looking for practical and reliable markers of fatigue is of particular interest in elite sports. One possible marker might be the autonomic nervous system activity, known to be well affected by physical exercise and that can be easily assessed by heart rate variability.
  
  
  METHODS
  We designed a laboratory study to follow six sedentary subjects (32.7 +/- 5.0 yr) going successively through 2 months of intensive physical training and 1 month of overload training on cycloergometer followed by 2 wk of recovery. Maximal power output over 5 min (Plim5'), VO(2) and standard indices of heart rate variability were monitored all along the protocol.
  
  
  RESULTS
  During the intensive training period, physical performance increased significantly VO(2peak) : +20.2%, < 0.01; Plim5': +26.4%, < 0.0001) as well as most of the indices of heart rate variability (mean RR, Ptot, HF, rMSSD, pNN50, SDNNIDX, SDNN, all < 0.05) with a significant shift in the autonomic nervous system toward a predominance of its parasympathetic arm (LF/HF, LFnu, HFnu, < 0.01). During the overload training period, there was a stagnation of the parasympathetic indices associated to a progressive increase in sympathetic activity (LF/HF, < 0.05). During the week of recovery, there was a sudden significant rebound of the parasympathetic activity (mean RR, HF, pNN50, rMSSD, all < 0.05). After 7 wk of recovery, all heart rate variability indices tended to return to the prestudy values.
  
  
  CONCLUSIONS
  Autonomic nervous system status depends on cumulated physical fatigue due to increased training loads. Therefore, heart rate variability analysis appears to be an appropriate tool to monitor the effects of physical training loads on performance and fitness, and could eventually be used to prevent overtraining states.
authors.affiliation: Laboratorie de Physiologie, GIP E2S, Université de Saint-Etienne, France. Vincent.Pichot@univ-st-etienne.fr
authors.forename: Vincent
authors.initials: V
authors.lastname: Pichot
authors.forename: Thierry
authors.initials: T
authors.lastname: Busso
authors.forename: Frédéric
authors.initials: F
authors.lastname: Roche
authors.forename: Martin
authors.initials: M
authors.lastname: Garet
authors.forename: Frédéric
authors.initials: F
authors.lastname: Costes
authors.forename: David
authors.initials: D
authors.lastname: Duverney
authors.forename: Jean-René
authors.initials: JR
authors.lastname: Lacour
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Barthélémy
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D002940:Circadian Rhythm; D005080:Exercise Test; D006339:Heart Rate; D006801:Humans; D008297:Male; D010806:Physical Education and Training; D005082:Physical Exertion / Q000502:physiology*; D012146:Rest; D013997:Time Factors