title: Lactic acidosis, potassium, and the heart rate deflection point in professional road cyclists.
abstract: OBJECTIVE
  To determine the influence of lactic acidosis, the Bohr effect, and exercise induced hyperkalaemia on the occurrence of the heart rate deflection point (HRDP) in elite (professional) cyclists.
  
  
  METHODS
  Sixteen professional male road cyclists (mean (SD) age 26 (1) years) performed a ramp test on a cycle ergometer (workload increases of 5 W/12 s, averaging 25 W/min). Heart rate (HR), gas exchange parameters, and blood variables (lactate, pH, P(50) of the oxyhaemoglobin dissociation curve, and K(+)) were measured during the tests.
  
  
  RESULTS
  A HRDP was shown in 56% of subjects at about 88% of their maximal HR (HRDP group; n = 9) but was linear in the rest (No-HRDP group; n = 7). In the HRDP group, the slope of the HR-workload regression line above the HRDP correlated inversely with levels of K(+) at the maximal power output (r = -0.67; p<0.05).
  
  
  CONCLUSIONS
  The HRDP phenomenon is associated, at least partly, with exercise induced hyperkalaemia.
authors.affiliation: Departamento de Ciencias Morfológicas y Fisiología, Universidad Europea de Madrid, Madrid, Spain. alejandro.lucia@mrfs.cisa.uem.es
authors.forename: A
authors.initials: A
authors.lastname: Lucía
authors.forename: J
authors.initials: J
authors.lastname: Hoyos
authors.forename: A
authors.initials: A
authors.lastname: Santalla
authors.forename: M
authors.initials: M
authors.lastname: Pérez
authors.forename: A
authors.initials: A
authors.lastname: Carvajal
authors.forename: J L
authors.initials: JL
authors.lastname: Chicharro
mesh_terms: D000140:Acidosis, Lactic / Q000097:blood*; D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D001642:Bicycling / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D006947:Hyperkalemia / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D008297:Male; D010807:Physical Endurance / Q000502:physiology; D011188:Potassium / Q000097:blood*
chemical_list: D019344:Lactic Acid; D011188:Potassium