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1 Astrand Laboratory, Swedish School of Sports and Health, Sweden
2 Department of Laboratory Medicine, Section of Clinical Physiology, Karolinska Institute, Stockholm, Sweden
* To whom correspondence should be addressed. E-mail: bjorn.ekblom{at}gih.se.
We tested the hypothesis that the work of the heart was not a limiting factor in the attainment of maximal oxygen uptake (VO2max). We measured cardiac output (Q) and blood pressures (BP) during exercise at two different rates of maximal work in order to estimate the work of the heart through calculation of the rate-pressure product, as a part of the ongoing discussion regarding factors limiting VO2max. Eight well-trained males (age24.4±2.8yrs, weight 81.3±7.8 kg and VO2max 59.1±2.0 ml . min-1 . kg-1) performed two maximal combined arm and leg exercises, differing 10% in watts, with average duration of time to exhaustion of 4min 50sec and 3min 40sec, respectively. There were no differences between work rates in measured VO2max, Qmax and peak HR between work rates (0.02 l . min-1, 0.3 l . min-1 and 0.8 beats . min-1, respectively) but the systolic, diastolic and calculated mean BP were significantly higher (19, 5 and 10 mmHg, respectively) in the higher (H) than in the lower (L) maximal work rate. The products of HR times systolic or mean BP and Q times systolic or mean BP were significantly higher (3715, 1780, 569 and 1780, respectively) during the H than the L work rate. Differences in these four products indicate a higher mechanical work of the heart on H than L maximal work rate. Therefore, this study does not support the central governor theory, which states that the work of the heart and consequently VO2max, during maximal exercise is protected from being ischemic.
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