title: Nocturnal heart rate variability following supramaximal intermittent exercise.
abstract: OBJECTIVE
  To assess the effect of supramaximal intermittent exercise on long-term cardiac autonomic activity, inferred from heart rate variability (HRV).
  
  
  METHODS
  Eleven healthy males performed a series of two consecutive intermittent 15-s runs at 95% VIFT (i.e., speed reached at the end of the 30-15 Intermittent Fitness Test) interspersed with 15 s of active recovery at 45% VIFT until exhaustion. Beat-to-beat intervals were recorded during two consecutive nights (habituation night and 1st night) before, 10 min before and immediately after exercise, as well as 12 h (2nd night) and 36 h (3rd night) after supramaximal intermittent exercise. The HRV indices were calculated from the last 5 min of resting and recovery periods, and the first 10 min of the first estimated slow wave sleep period.
  
  
  RESULTS
  Immediate post-supramaximal exercise vagal-related HRV indices were significantly lower than immediate pre-supramaximal exercise values (P < .001). Most vagal-related indices were lower during the 2nd night compared with the 1st night (eg, mean RR intervals, P = .03). Compared with the 2nd night, vagal-related HRV indices were significantly higher during the 3rd night. Variables were not different between the 1st and 3rd nights; however, we noted a tendency (adjusted effect size, aES) for an increased normalized high-frequency component (P = .06 and aES = 0.70) and a tendency toward a decreased low-frequency component (P = .06 and aES = 0.74).
  
  
  CONCLUSIONS
  Results confirm the strong influence of exercise intensity on short- and long-term postexercise heart rate variability recovery and might help explain the high efficiency of supramaximal training for enhancing indices of cardiorespiratory fitness.
authors.affiliation: Laboratoire de Recherche, EA 3300, Faculté des Sciences du Sport, Université de Picardie Jules Verne, Amiens, France.
authors.forename: Hani
authors.initials: H
authors.lastname: Al Haddad
authors.forename: Paul B
authors.initials: PB
authors.lastname: Laursen
authors.forename: Said
authors.initials: S
authors.lastname: Ahmaidi
authors.forename: Martin
authors.initials: M
authors.lastname: Buchheit
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010806:Physical Education and Training / Q000379:methods*; D010807:Physical Endurance / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology
chemical_list: D019344:Lactic Acid