title: Sport modality affects bradycardia level and its mechanisms of control in professional athletes.
abstract: We investigated the influence of sport modalities in resting bradycardia and its mechanisms of control in highly trained athletes. In addition, the relationships between bradycardia mechanisms and cardiac structural adaptations were tested. Professional male athletes (13 runners, 11 cyclists) were evaluated. Heart rate (HR) was recorded at rest on beat-to-beat basis (ECG). Selective pharmacological blockade was performed with atropine and esmolol. Vagal effect, intrinsic heart rate (IHR), parasympathetic (n) and sympathetic (m) modulations, autonomic influence (AI) and autonomic balance (Abal) were calculated. Plasmatic norepinephrine (high-pressure liquid chromatography) and cardiac structural adaptations (echocardiography) were evaluated. Runners presented lower resting HR, higher vagal effect, parasympathetic modulation (n), AI and IHR than cyclists (P<0.05). Abal, sympathetic modulation (m) and norepinephrine level were similar within athletes regardless of modality. The cardiac chambers were also similar between runners and cyclists (P=0.30). However, cyclists displayed higher septum and posterior wall thickness than runners (P=0.04). Further analysis showed a trend towards inverse correlation between IHR with septum wall thickness and posterior wall thickness (P=0.056). Type of sport influences the resting bradycardia level and its mechanisms of control in professional athletes. Resting bradycardia in runners is mainly dependent on an autonomic mechanism. In contrast, a cyclist's resting bradycardia relies on a non-autonomic mechanism probably associated with combined eccentric and concentric hypertrophy.
authors.affiliation: Heart Institute (InCor), Medical School of University of São Paulo, Cardiovascular Rehabilitation and Exercise Physiology Unit, São Paulo, Brazil.
authors.forename: L F
authors.initials: LF
authors.lastname: Azevedo
authors.affiliation: Heart Institute (InCor), Medical School of University of São Paulo, Cardiovascular Rehabilitation and Exercise Physiology Unit, São Paulo, Brazil.
authors.forename: P S
authors.initials: PS
authors.lastname: Perlingeiro
authors.affiliation: Heart Institute (InCor), Medical School of University of São Paulo, Clinical -Arrhythmia Unit, São Paulo, Brazil.
authors.forename: D T
authors.initials: DT
authors.lastname: Hachul
authors.affiliation: Heart Institute (InCor), Medical School of University of São Paulo, Cardiovascular Rehabilitation and Exercise Physiology Unit, São Paulo, Brazil.
authors.forename: I L
authors.initials: IL
authors.lastname: Gomes-Santos
authors.affiliation: School of Physical Education and Sport, University of São Paulo, -Biodynamic of the Movement of the Human Body, São Paulo, Brazil.
authors.forename: P C
authors.initials: PC
authors.lastname: Brum
authors.affiliation: Mayo Clinic, Division of Cardiovascular Diseases and Internal Medicine, Rochester, United States.
authors.forename: T G
authors.initials: TG
authors.lastname: Allison
authors.affiliation: Heart Institute (InCor), Medical School of University of São Paulo, Cardiovascular Rehabilitation and Exercise Physiology Unit, São Paulo, Brazil.
authors.forename: C E
authors.initials: CE
authors.lastname: Negrão
authors.affiliation: Heart Institute (InCor), Medical School of University of São Paulo, Cardiovascular Rehabilitation and Exercise Physiology Unit, São Paulo, Brazil.
authors.forename: L D N J
authors.initials: LD
authors.lastname: De Matos
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D006321:Heart / Q000033:anatomy & histology / Q000294:innervation / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D010806:Physical Education and Training; D010807:Physical Endurance / Q000502:physiology*; D011446:Prospective Studies; D012420:Running / Q000502:physiology*; D013550:Swimming / Q000502:physiology*; D055815:Young Adult