title: Evidence of cardiac functional reserve upon exhaustion during incremental exercise to determine VO2max.
abstract: BACKGROUND
  There remains considerable debate regarding the limiting factor(s) for maximal oxygen uptake (VO2max). Previous studies have shown that the central circulation may be the primary limiting factor for VO2max and that cardiac work increases beyond VO2max.
  
  
  OBJECTIVE
  We sought to evaluate whether the work of the heart limits VO2max during upright incremental cycle exercise to exhaustion.
  
  
  METHODS
  Eight trained men completed two incremental exercise trials, each terminating with exercise at two different rates of work eliciting VO2max (MAX and SUPRAMAX). During each exercise trial we continuously recorded cardiac output using pulse-contour analysis calibrated with a lithium dilution method. Intra-arterial pressure was recorded from the radial artery while pulmonary gas exchange was measured continuously for an assessment of oxygen uptake.
  
  
  RESULTS
  The workload during SUPRAMAX (mean±SD: 346.5±43.2 W) was 10% greater than that achieved during MAX (315±39.3 W). There was no significant difference between MAX and SUPRAMAX for Q (28.7 vs 29.4 L/min) or VO2 (4.3 vs 4.3 L/min). Mean arterial pressure was significantly higher during SUPRAMAX, corresponding to a higher cardiac power output (8.1 vs 8.5 W; p<0.06).
  
  
  CONCLUSIONS
  Despite similar VO2 and Q, the greater cardiac work during SUPRAMAX supports the view that the heart is working submaximally at exhaustion during an incremental exercise test (MAX).
authors.affiliation: School of Life Sciences, Kingston University, Surrey, UK Discipline of Physiology, University of Adelaide, Adelaide, Australia.
authors.forename: Adrian D
authors.initials: AD
authors.lastname: Elliott
authors.affiliation: The Children's Hospital at Westmead, Sydney, Australiai Discipline of Paediatrics and Child Health, The University of Sydney, Sydney, Australia.
authors.forename: Justin
authors.initials: J
authors.lastname: Skowno
authors.affiliation: Freeman Hospital, Newcastle Upon Tyne, UK.
authors.forename: Mahesh
authors.initials: M
authors.lastname: Prabhu
authors.affiliation: UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, Newlands, South Africa.
authors.forename: Timothy David
authors.initials: TD
authors.lastname: Noakes
authors.affiliation: School of Psychology and Sports Sciences, Northumbria University, Newcastle Upon Tyne, UK.
authors.forename: Les
authors.initials: L
authors.lastname: Ansley
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology; D006321:Heart / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology
keywords: Aerobic fitness/Vo2 Max; Cardiovascular; Cycling; Exercise physiology; Fatigue