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Evidence of cardiac functional reserve upon exhaustion during incremental exercise to determine VO2max
  1. Adrian D Elliott1,2,
  2. Justin Skowno3,4,
  3. Mahesh Prabhu5,
  4. Timothy David Noakes6,
  5. Les Ansley7
  1. 1School of Life Sciences, Kingston University, Surrey, UK
  2. 2Discipline of Physiology, University of Adelaide, Adelaide, Australia
  3. 3The Children's Hospital at Westmead, Sydney, Australiai
  4. 4Discipline of Paediatrics and Child Health, The University of Sydney, Sydney, Australia
  5. 5Freeman Hospital, Newcastle Upon Tyne, UK
  6. 6UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, Newlands, South Africa
  7. 7School of Psychology and Sports Sciences, Northumbria University, Newcastle Upon Tyne, UK
  1. Correspondence to Dr Adrian Elliott, School of Medical Sciences, University of Adelaide, Adelaide, 5062, Australia; adrian.elliott{at}adelaide.edu.au

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.

Aim 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).

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