title: Submaximal exercise intensity modulates acute post-exercise heart rate variability.
abstract: OBJECTIVE
  This study investigated whether short-term heart rate variability (HRV) can be used to differentiate between the immediate recovery periods following three different intensities of preceding exercise.
  
  
  METHODS
  12 males cycled for 8 min at three intensities: LOW (40-45 %), MOD (75-80 %) and HIGH (90-95 %) of heart rate (HR) reserve. HRV was assessed during exercise and throughout 10-min seated recovery.
  
  
  RESULTS
  1-min HR recovery was reduced following greater exercise intensities when expressed as R-R interval (RRI, ms) (p < 0.001), but not b min(-1) (p = 0.217). During exercise, the natural logarithm of root mean square of successive differences (Ln-RMSSD) was higher during LOW (1.66 ± 0.47 ms) relative to MOD (1.14 ± 0.32 ms) and HIGH (1.30 ± 0.25 ms) (p ≤ 0.037). Similar results were observed for high-frequency spectra (Ln-HF-LOW: 2.9 ± 1.0; MOD: 1.6 ± 0.6; HIGH: 1.6 ± 0.3 ms(2), p < 0.001). By 1-min recovery, higher preceding exercise intensities resulted in lower HRV amongst all three intensities for Ln-RMSSD (LOW: 3.45 ± 0.58; MOD: 2.34 ± 0.81; HIGH: 1.66 ± 0.78 ms, p < 0.001) and Ln-HF (LOW: 6.0 ± 1.0; MOD: 4.3 ± 1.4; HIGH: 2.8 ± 1.4 ms(2), p < 0.001). Similarly, by 1-min recovery 'HR-corrected' HRV (Ln-RMSSD: RRI × 10(3)) was different amongst all three intensities (LOW: 3.64 ± 0.49; MOD: 2.90 ± 0.65; HIGH: 2.40 ± 0.67, p < 0.001). These differences were maintained throughout 10-min recovery (p ≤ 0.027).
  
  
  CONCLUSIONS
  Preceding exercise intensity has a graded effect on recovery HRV measures reflecting cardiac vagal activity, even after correcting for the underlying HR. The immediate recovery following exercise is a potentially useful period to investigate autonomic activity, as multiple levels of autonomic activity can be clearly differentiated between using HRV. When investigating post-exercise HRV it is critical to account for the relative exercise intensity.
authors.affiliation: Discipline of Exercise and Sports Science, Faculty of Health Sciences, The University of Sydney, C103, Cumberland Campus, Lidcombe, NSW, 2141, Australia. scott.michael@sydney.edu.au.
authors.forename: Scott
authors.initials: S
authors.lastname: Michael
authors.affiliation: Discipline of Exercise and Sports Science, Faculty of Health Sciences, The University of Sydney, C103, Cumberland Campus, Lidcombe, NSW, 2141, Australia.
authors.forename: Ollie
authors.initials: O
authors.lastname: Jay
authors.affiliation: Discipline of Exercise and Sports Science, Faculty of Health Sciences, The University of Sydney, C103, Cumberland Campus, Lidcombe, NSW, 2141, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Halaki
authors.affiliation: New South Wales Institute of Sport, Sydney Olympic Park, NSW, Australia.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Graham
authors.affiliation: Discipline of Exercise and Sports Science, Faculty of Health Sciences, The University of Sydney, C103, Cumberland Campus, Lidcombe, NSW, 2141, Australia.
authors.forename: Glen M
authors.initials: GM
authors.lastname: Davis
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001341:Autonomic Nervous System / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate; D006801:Humans; D008297:Male; D011897:Random Allocation
keywords: Autonomic; HRV; Parasympathetic; Recovery; Vagal