title: Eight weeks of moderate-intensity exercise training increases heart rate variability in sedentary postmenopausal women.
abstract: BACKGROUND
  Regular exercise is associated with increased heart rate variability (HRV). However, results from studies examining the effect of exercise training on HRV in postmenopausal women are inconclusive. In addition, the effect of hormone replacement therapy (HRT) on HRV remains a subject of speculation.
  
  
  METHODS
  We examined 88 sedentary postmenopausal women in a randomized controlled trial who were assigned to exercise (n = 49) or control (n = 39) groups. The exercising women performed 8 weeks of aerobic exercise training at a heart rate equivalent to 50% of VO2max, consisting on average of 44 minutes per session, 3 to 4 times per week. Resting HRV was measured in each participant at baseline and after 8 weeks of intervention. Ten minutes of resting R-R intervals were analyzed by time (standard deviation of mean R-R intervals, root of mean square successive differences) and frequency domain methods: low-frequency (LF) was defined as 0.04 to 0.15 Hz, high-frequency (HF) as 0.15 to 0.40 Hz, and total spectral power as 0.00 to 0.40 Hz. The LF and HF components in normalized units were also calculated.
  
  
  RESULTS
  At baseline, there were no significant differences in HRV between control and exercise groups. Additionally, there were no differences in any HRV variables when women were grouped by HRT use (no HRT, estrogen-only HRT, and progestin-containing HRT). After 8 weeks, women randomly assigned to the exercise group increased all absolute time and frequency domain indexes (all P <.001) and reduced resting heart rate (P =.002) compared with women in the control group. The LF and HF components expressed as normalized units remained unchanged after exercise intervention. Additionally, HRT use did not modify the exercise-induced changes in HRV.
  
  
  CONCLUSIONS
  We conclude that moderate aerobic exercise increases HRV in sedentary postmenopausal women. This benefit is not influenced by the use of HRT.
authors.affiliation: The Cooper Institute, Dallas, Tex 75230, USA. djurca@cooperinst.org
authors.forename: Radim
authors.initials: R
authors.lastname: Jurca
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Church
authors.forename: Gina M
authors.initials: GM
authors.lastname: Morss
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Jordan
authors.forename: Conrad P
authors.initials: CP
authors.lastname: Earnest
mesh_terms: D000704:Analysis of Variance; D001795:Blood Pressure Determination; D015914:Estrogen Replacement Therapy; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D010101:Oxygen Consumption; D017698:Postmenopause / Q000502:physiology*