title: [Polar S810 as an alternative resource to the use of the electrocardiogram in the 4-second exercise test].
abstract: BACKGROUND
  The 4-second exercise test (T4s) evaluates the cardiac vagal tone during the initial heart rate (HR) transient at sudden dynamic exercise, through the identification of the cardiac vagal index (CVI) obtained from the electrocardiogram (ECG).
  
  
  OBJECTIVE
  To evaluate the use of the Polar S810 heart rate monitor (HRM) as an alternative resource to the use of the electrocardiogram in the 4-second exercise test.
  
  
  METHODS
  In this study, 49 male individuals (25 +/- 20 years, 176 +/-12 cm, 74 +/- 6 kg) underwent the 4-second exercise test. The RR intervals were recorded simultaneously by ECG and HRM. We calculated the mean and the standard deviation of the last RR interval of the pre-exercise period, or of the first RR interval of the exercise period, whichever was longer (RRB), of the shortest RR interval of the exercise period (RRC), and of the CVI obtained by ECG and HRM. We used the Student t-test for dependent samples (p < or 0.05) to test the significance of the differences between means. To identify the correlation between the ECG and the HRM, we used the linear regression to calculate the Pearson's correlation coefficient and the strategy proposed by Bland and Altman.
  
  
  RESULTS
  Linear regression showed r(2) of 0.9999 for RRB, 0.9997 for RRC, and 0.9996 for CVI. Bland e Altman strategy presented standard deviation of 0.92 ms for RRB, 0.86 ms for RRC, and 0.002 for CVI.
  
  
  CONCLUSIONS
  Polar S810 HRM was more efficient in the application of T4s compared to the ECG.
authors.affiliation: Laboratório de Avaliação Motora, Universidade Federal de Juiz de Fora.
authors.forename: Alan Santos
authors.initials: AS
authors.lastname: Pimentel
authors.forename: Eduardo da Silva
authors.initials: Eda S
authors.lastname: Alves
authors.forename: Rafael de Oliveira
authors.initials: Rde O
authors.lastname: Alvim
authors.forename: Rogério Tasca
authors.initials: RT
authors.lastname: Nunes
authors.forename: Carlos Magno Amaral
authors.initials: CM
authors.lastname: Costa
authors.forename: Júlio Cesar Moraes
authors.initials: JC
authors.lastname: Lovisi
authors.forename: Jorge Roberto
authors.initials: JR
authors.lastname: Perrout de Lima
mesh_terms: D000328:Adult; D004562:Electrocardiography / Q000295:instrumentation*; D022062:Electrophysiologic Techniques, Cardiac / Q000295:instrumentation* / Q000379:methods; D004812:Epidemiologic Methods; D005080:Exercise Test / Q000295:instrumentation* / Q000379:methods; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D014630:Vagus Nerve / Q000502:physiology