title: Autonomic recovery after exercise in trained athletes: intensity and duration effects.
abstract: OBJECTIVE
  To investigate the effects of training intensity and duration, through a range representative of training in endurance athletes, on acute recovery of autonomic nervous system (ANS) balance after exercise.
  
  
  METHODS
  Nine highly trained (HT) male runners (VO2max 72 +/- 5 mL.kg.min(-1), 14 +/- 3 training hours per week) and eight trained (T) male subjects (VO2max 60 +/- 5 mL.kg.min(-1), 7 +/- 1 training hours per week) completed preliminary testing to determine ventilatory thresholds (VT1, VT2) and VO2max. HT performed four intensity-controlled training sessions: 60 min and 120 min below VT1; 60 min with 30 min between VT1 and VT2 (threshold); and 60 min above VT2 (6 x 3 min at 96% VO2max, 2 min of recovery). T also completed the interval session to compare ANS recovery between HT and T. Supine heart rate variability (HRV) was quantified at regular intervals through 4 h of recovery.
  
  
  RESULTS
  When HT ran 60 or 120 min below VT1, HRV returned to pretraining values within 5-10 min. However, training at threshold (2.7 +/- 0.4 mM) or above VT2 (7.1 +/- 0.7 mM) induced a significant, but essentially identical, delay of HRV recovery (return to baseline by approximately 30 min). In T, HRV recovery was significantly slower, with HRV returning to baseline by >or=90 min after the same interval session.
  
  
  CONCLUSIONS
  In the highly trained endurance athlete, exercise for <or=120 min below the first ventilatory threshold causes minimal disturbance in ANS balance. ANS recovery is more rapid in highly trained than in trained subjects after high-intensity exercise. Further, the first ventilatory threshold may demarcate a "binary" threshold for ANS/HRV recovery in highly trained athletes, because further delays in HRV recovery with even higher training intensities were not observed.
authors.affiliation: Faculty of Health and Sport, Agder University College, Kristiansand, Norway. stephen.seiler@hia.no
authors.forename: Stephen
authors.initials: S
authors.lastname: Seiler
authors.forename: Olav
authors.initials: O
authors.lastname: Haugen
authors.forename: Erin
authors.initials: E
authors.lastname: Kuffel
mesh_terms: D000293:Adolescent; D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D015444:Exercise; D006339:Heart Rate; D006801:Humans; D008297:Male; D009664:Norway; D010807:Physical Endurance / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness; D020127:Recovery of Function / Q000502:physiology*