title: Heart rate variability during exercise performed below and above ventilatory threshold.
abstract: OBJECTIVE
  To examine whether differences in heart rate variability (HRV) can distinguish sub- from supra-ventilatory-threshold exercise and whether the exercise duration at supra-threshold intensity alters cardiorespiratory synchronization.
  
  
  METHODS
  Beat-to-beat RR interval, VO2, VCO2, VE, and blood lactate concentration of 11 healthy well-trained young subjects were collected during two exercise tests: 1) a moderate-intensity test: 15 min performed below the power at ventilatory threshold (pVT); and 2) a heavy-intensity test: above pVT until exhaustion. Fast Fourier transform, smoothed pseudo Wigner-Ville distribution, and complex demodulation were applied to RR time series.
  
  
  RESULTS
  1) Moderate exercise shows a prevalence of low-frequency (LF) spectral energy compared with the high-frequency (HF) one (LF = 80 +/- 10% vs HF = 20 +/- 10%, P < 0.001), whereas the reverse is observed during heavy exercise (LF = 11 +/- 8% vs HF = 89 +/- 8%, P < 0.001). 2) During heavy exercise, the HF amplitude and the tidal volume (Vt) remained constant, whereas the breathing frequency (BF) increased (BF: 0.70 +/- 0.18 vs 0.93 +/- 0.31, P < 0.01) and mean RR decreased (342 +/- 15 vs 317 +/- 16, P < 0.01). Despite the RR series and the breathing signal remaining synchronized, HR/BF ratio decreased and stabilized at 3 RR for one breathing cycle, whatever the initial ratio.
  
  
  CONCLUSIONS
  1) HRV allows us to differentiate sub- from supra-ventilatory-threshold exercise and 2) exercise duration at supra-threshold intensity does not alter the cardiorespiratory synchronization.
authors.affiliation: Laboratory of Exercise Physiology and Genetics, Department of Sport and Exercise Science, University of Evry, Evry Cedex, France. francois.cottin@bp.univ-evry.fr
authors.forename: Francois
authors.initials: F
authors.lastname: Cottin
authors.forename: Claire
authors.initials: C
authors.lastname: Médigue
authors.forename: Pierre-Marie
authors.initials: PM
authors.lastname: Leprêtre
authors.forename: Yves
authors.initials: Y
authors.lastname: Papelier
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Koralsztein
authors.forename: Véronique
authors.initials: V
authors.lastname: Billat
mesh_terms: D000293:Adolescent; D015308:Anaerobic Threshold / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D005583:Fourier Analysis; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D011659:Pulmonary Gas Exchange / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology*; D013177:Sports
chemical_list: D019344:Lactic Acid