title: Beta1-adrenoceptor mediated origin of the heart rate performance curve deflection.
abstract: OBJECTIVE
  The deflection of the HR performance curve (HRPC) has been described as an objective marker of submaximal exercise performance. HR response to incremental cycle ergometer exercise is shown to be neither linear nor uniform and a physiological explanation of the deflection phenomenon is lacking. We hypothesized that differences in the beta1-adrenoceptor site are the source of these differences. The aim of the study was to investigate the influence of the highly selective beta1-adrenoceptor (beta1-AR) antagonist bisoprolol (Bi) on the HRPC in young healthy male subjects with different HR response patterns.
  
  
  METHODS
  Sixteen subjects were treated in randomized order with Bi or a placebo (Pl) in two separate trials. HR response during incremental cycle ergometer exercise was compared between the two trials. Blood lactate concentration (La) and ventilatory variables were measured throughout both tests.
  
  
  RESULTS
  Bi changed the direction of the HRPC more in subjects with a regular, s-shaped response pattern under placebo than those with a nonregular or linear pattern. The influence of Bi on the HR at the second lactate turn point was significantly related (R = 0.78; P < 0.001) to the pattern of the HRPC in Pl conditions.
  
  
  CONCLUSIONS
  We suggest that differences between the subjects with regular s-shaped versus nonregular HRPC may be due to differences at the beta1-AR site. The origin of the HRPC deflection is mediated in part by the beta1-AR sensitivity.
authors.affiliation: Institute of Sports Science, University of Graz, Graz, Austria.
authors.forename: Peter
authors.initials: P
authors.lastname: Hofmann
authors.forename: Manfred
authors.initials: M
authors.lastname: Wonisch
authors.forename: Rochus
authors.initials: R
authors.lastname: Pokan
authors.forename: Günther
authors.initials: G
authors.lastname: Schwaberger
authors.forename: Gerhard
authors.initials: G
authors.lastname: Smekal
authors.forename: Serge P
authors.initials: SP
authors.lastname: von Duvillard
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D017298:Bisoprolol / Q000494:pharmacology*; D005080:Exercise Test; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007773:Lactates / Q000097:blood; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D018342:Receptors, Adrenergic, beta-1 / Q000502:physiology*
chemical_list: D000319:Adrenergic beta-Antagonists; D007773:Lactates; D018342:Receptors, Adrenergic, beta-1; D017298:Bisoprolol