title: Spectral analysis of heart rate variability during exercise in trained subjects.
abstract: OBJECTIVE
  To investigate the effects of strenuous exercise on heart rate variability (HRV).
  
  
  METHODS
  We evaluated the effects of exercise intensity and duration on HRV indices in 14 healthy trained subjects. Each subject exercised for 3, 6, and 9 min at 60 and 70% of the power achieved at maximal oxygen consumption (PVO2(max)) and for 3 and 6 min (or 3 min twice) at 80% of PVO2(max). The electrocardiogram RR intervals were recorded then processed by fast(FFT) and short-time (STFT) Fourier transform for determination of low-frequency (LF, 0.045-0.15 Hz) and high-frequency (HF, 0.15-1.0 Hz) components.
  
  
  RESULTS
  The LF and HF components expressed as absolute power (ms2) decreased significantly at the onset of exercise (P < 0.05). However, with increasing exercise intensity, the HF component expressed as normalized units (n.u.) (reflecting parasympathetic modulation) increased significantly, whereas the LF component (n.u.) and LF/HF ratio (both reflecting sympathetic modulation) decreased significantly (P < 0.05). STFT showed that increasing exercise intensity was associated with a shift in HF peak frequency related to an increase in respiratory rate and a marked decrease in LF power (ms2). Moreover, HFn.u. rose (r = 0.918, P < 0.01) and LFms2 fell as minute ventilation increased (r = 0.906, P < 0.01).
  
  
  CONCLUSIONS
  Parasympathetic respiratory control and nonautonomic mechanisms may influence the HF-peak shift during strenuous exercise. HRV and the usual indexes of sympathetic activity do not accurately reflect changes in autonomic modulation during exhaustive exercise.
authors.affiliation: Laboratory of Exercise Induced Physiological Adaptations, School of Sports Science, Poitiers, France. aurelien.pichon@orange.fr
authors.forename: Aurélien P
authors.initials: AP
authors.lastname: Pichon
authors.forename: Claire
authors.initials: C
authors.lastname: de Bisschop
authors.forename: Manuel
authors.initials: M
authors.lastname: Roulaud
authors.forename: André
authors.initials: A
authors.lastname: Denjean
authors.forename: Yves
authors.initials: Y
authors.lastname: Papelier
mesh_terms: D000328:Adult; D004562:Electrocardiography; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005583:Fourier Analysis; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology; D013057:Spectrum Analysis; D013564:Sympathetic Nervous System / Q000502:physiology
chemical_list: D010100:Oxygen