Enhanced cardiac vagal efferent activity does not explain training-induced bradycardia

• Published in: Autonomic neuroscience 2004-05, Vol.112 (1), p.60-68
• Main Authors: Scott, Adrienne S., Eberhard, André, Ofir, Dror, Benchetrit, Gila, Dinh, Tuan Pham, Calabrese, Pascale, Lesiuk, Veronika, Perrault, Hélène
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Analysis of Variance; Arrhythmia, Sinus; Arrhythmia, Sinus - physiopathology; Biological and medical sciences; Blood Pressure; Blood Pressure - physiology; Bradycardia; Bradycardia - physiopathology; Cardiac dysrhythmias; Cardiac vagal efferent activity; Cardiology. Vascular system; Case-Control Studies; Efferent Pathways; Efferent Pathways - physiology; Exercise training-induced bradycardia; Female; Fourier Analysis; Fundamental and applied biological sciences. Psychology; Heart; Heart Rate; Heart Rate - physiology; Heart rate variability; Human health and pathology; Humans; Life Sciences; Male; Medical sciences; Peripheral nervous system. Autonomic nervous system. Neuromuscular transmission. Ganglionic transmission. Electric organ; Physical Endurance; Respiration; Respiratory sinus arrhythmia; Sports; Sports - physiology; Teaching; Teaching - methods; Tissues and Organs; Vagus Nerve; Vagus Nerve - physiology; Vertebrates: nervous system and sense organs
• ISSN: 1566-0702; 1872-7484
• DOI: 10.1016/j.autneu.2004.04.006

Studies of heart rate variability (HRV) have so far produced contradictory evidence to support the common belief that endurance training enhances cardiac parasympathetic tone. This may be related to the fact that most studies failed to specifically isolate the vagally mediated influence of respiration. This study used a cross-sectional comparison of endurance athletes ( n=20; ATHL) exhibiting resting bradycardia and age-matched nonathletes ( n=12; CRTL) to indirectly assess training effects on amplitude and timing characteristics of respiratory sinus arrhythmia (RSA). Continuous electrocardiogram (ECG) and ventilatory flows were recorded during spontaneous breathing (SP), as well as during breathing at four cycles less than (M4) or more (P4) than SP, to also examine potential repercussions of training on the sensitivity of the cardiac vagal responses to breathing. A fast Fourier transform procedure was used to quantify the standard spectral high-frequency (HF) and low-frequency (LF) components and a respiratory-centered frequency (RCF) component of HRV. RSA was assessed using a breath-by-breath quantification of the amplitude and timing of the maximum change in instantaneous heart rate. Under baseline SP conditions, heart rate was lower in ATHL (62.6±6.5 vs. 75.2±9 beats/min; p