title: Cardiac autonomic responses at onset of exercise: effects of aerobic fitness.
abstract: Analyzes of cardiac autonomic responses at the initial transient of exercise have been used for the investigation of the cardiovascular health. We evaluated the influence of aerobic fitness on HR and HRV responses at the onset of exercise. 25 male subjects (22.3±2.4 years) were divided into 2 groups: 'low aerobic fitness' (36.2±2.6ml.kg(-1).min(-1); n=10) and 'high aerobic fitness' (46.4±5.0ml.kg(-1).min(-1); n=15). The experimental session consisted of assessing the beat-to-beat HR at rest and during submaximal exercise. The autonomic responses at the onset of exercise were calculated by fitting the HR and HRV (rMSSD-index) curves during the initial 300s of exercise into a first-order exponential equation. The time constant of HR and of the rMSSD index (τonHR and τonrMSSD) were calculated for analysis. We observed lower values of τonrMSSD in the high aerobic fitness group compared to the low aerobic fitness group (26.8±5s vs. 38.0±18s, respectively; p=0.02). The τonHR (42.0±15 vs. 49.3±26s, p=0.38) for the groups showed no difference. Aerobic fitness partially influenced the autonomic responses during exercise, since individuals with higher fitness showed faster decreases in beat-to-beat HRV at the onset of exercise.
authors.affiliation: Laboratory of Motor Assessment, Faculty of Physical Education and Sports, Federal University of Juiz de Fora, Minas Gerais, Brazil.
authors.forename: T
authors.initials: T
authors.lastname: D'Agosto
authors.affiliation: Exercise Hemodynamic Laboratory, School of Physical Education and Sport, University of São Paulo, Sao Paulo, Brazil.
authors.forename: T
authors.initials: T
authors.lastname: Peçanha
authors.affiliation: Biomedical Engineering Program (COPPE), Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: R
authors.initials: R
authors.lastname: Bartels
authors.affiliation: Laboratory of Motor Assessment, Faculty of Physical Education and Sports, Federal University of Juiz de Fora, Minas Gerais, Brazil.
authors.forename: D N
authors.initials: DN
authors.lastname: Moreira
authors.affiliation: Faculty of Physiotherapy, Federal University of Juiz de Fora, Minas Gerais, Brazil.
authors.forename: L P
authors.initials: LP
authors.lastname: Silva
authors.affiliation: Laboratory of Exercise Sciences - LACE, Graduate Program in Cardiovascular Sciences, Department of Physiology and Pharmacology, Fluminense Federal University, Rio de Janeiro, Brazil.
authors.forename: A C L
authors.initials: AC
authors.lastname: Nóbrega
authors.affiliation: Laboratory of Motor Assessment, Faculty of Physical Education and Sports, Federal University of Juiz de Fora, Minas Gerais, Brazil.
authors.forename: J R P
authors.initials: JR
authors.lastname: Lima
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D010275:Parasympathetic Nervous System / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult