title: Unaltered R-R interval variability and bradycardia in cyclists as compared with non-athletes.
abstract: OBJECTIVE
  To test whether elite mountain bikers display a cardiac autonomic modulation pattern that is distinctive from that of active non-athletes.
  
  
  BACKGROUND
  The relationship between autonomic adaptation and bradycardia during physical exercise, including high-performance sports such as the mountain biking, remains to be elucidated.
  
  
  METHODS
  Twelve elite mountain bikers and 11 matched non-athletes controls were evaluated for time- and frequency-domain heart rate variability based on a 5-min ECG R-R intervals series obtained in both the supine and the orthostatic positions. Oxygen uptake and pulse rate were obtained at ventilatory thresholds and peak effort during an incremental cardiopulmonary exercise test. Significance of differences between medians (25th, 75th percentiles) from the two groups was evaluated by the Mann-Whitney test at p ≤ 0.05.
  
  
  RESULTS
  Athletes had lower heart rate [50 (47, 59) versus 63 (60, 69) bpm; p = 0.0004] and higher cardiopulmonary performance than controls [70.9 (64.6, 74.4) versus 47.7 (41.0, 51.9) mL (kg min)(-1); p = 0.01]. No statistical difference was found in heart rate variability in the group of athletes (p = 0.17-0.97), except for trend toward having lower coefficient of variation and low-frequency absolute power indices both in supine position (p = 0.06).
  
  
  CONCLUSIONS
  Bradycardia and higher oxygen uptake were found in association with unaltered cardiac autonomic modulation in elite mountain bikers athletes in supine and orthostatic positions, compared to active non-athletes. This bradycardia was not dependent on distinctive resting autonomic modulation. Intrinsic adaptation of sinus node and/or a peculiar state of autonomic adaptation to this exercise can be possible mechanisms.
authors: Cardiovascular Laboratory, Clinical Medicine Area, Faculty of Medicine, University of Brasilia, 70910-900 Brasilia, DF, Brazil. gmolina@unb.br
authors: Guilherme E
authors: GE
authors: Molina
authors: Luiz Guilherme G
authors: LG
authors: Porto
authors: Keila E
authors: KE
authors: Fontana
authors: Luiz F
authors: LF
authors: Junqueira
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D056352:Athletes; D001341:Autonomic Nervous System / Q000502:physiology*; D001642:Bicycling; D001919:Bradycardia; D005080:Exercise Test; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male
references: Med Sci Sports Exerc. 1998 May;30(5):691-6
references: 9588610
references: Am Heart J. 1994 May;127(5):1275-8
references: 8172056
references: Am Heart J. 1987 Jun;113(6):1489-94
references: 3591616
references: Braz J Med Biol Res. 2005 Apr;38(4):639-47
references: 15962191
references: J Appl Physiol (1985). 1993 Nov;75(5):2310-7
references: 8307890
references: J Hum Hypertens. 2010 Mar;24(3):175-82
references: 19554028
references: Circulation. 2001 Apr 17;103(15):1977-83
references: 11306527
references: Can J Appl Physiol. 1996 Apr;21(2):109-19
references: 8727474
references: Eur J Appl Physiol. 2005 Aug;94(5-6):681-9
references: 15906077
references: Med Sci Sports Exerc. 1998 Feb;30(2):206-14
references: 9502347
references: Pacing Clin Electrophysiol. 2009 Jan;32(1):43-51
references: 19140912
references: Heart Fail Rev. 2011 Mar;16(2):109-27
references: 20577901
references: Clin Physiol. 2001 Mar;21(2):238-45
references: 11318832
references: Auton Neurosci. 2004 May 31;112(1-2):60-8
references: 15233931
references: Proc (Bayl Univ Med Cent). 2010 Oct;23(4):368-70
references: 20944759
references: Cardiovasc Res. 1993 Mar;27(3):482-8
references: 8490949
references: Eur Heart J. 1996 Mar;17(3):354-81
references: 8737210
references: J Am Coll Cardiol. 2002 Mar 20;39(6):1033-8
references: 11897447
references: Clin Physiol Funct Imaging. 2004 Jan;24(1):10-8
references: 14717743
references: Med Sci Sports Exerc. 2000 Oct;32(10):1729-36
references: 11039645
references: Med Sci Sports Exerc. 2001 Sep;33(9):1496-502
references: 11528338
references: Med Sci Sports Exerc. 2001 Aug;33(8):1394-8
references: 11474344
references: Am J Physiol Heart Circ Physiol. 2004 Nov;287(5):H1921-7
references: 15242837
references: Clin Chest Med. 1984 Mar;5(1):77-88
references: 6723245
references: Med Sci Sports Exerc. 1997 Nov;29(11):1482-90
references: 9372486
references: Scand J Med Sci Sports. 1997 Oct;7(5):274-8
references: 9338944
references: Ann Noninvasive Electrocardiol. 2005 Jan;10(1):88-101
references: 15649244