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- Title
On the mechanisms that limit oxygen uptake during exercise in acute and chronic hypoxia: role of muscle mass.
- Authors
Calbet, José A. L.; Rådegran, Göran; Boushel, Robert; Saltin, Bengt
- Abstract
Peak aerobic power in humans ( ) is markedly affected by inspired O2 tension ( ). The question to be answered in this study is what factor plays a major role in the limitation of muscle peak in hypoxia: arterial O2 partial pressure ( ) or O2 content ( )? Thus, cardiac output (dye dilution with Cardio-green), leg blood flow (thermodilution), intra-arterial blood pressure and femoral arterial-to-venous differences in blood gases were determined in nine lowlanders studied during incremental exercise using a large (two-legged cycle ergometer exercise: Bike) and a small (one-legged knee extension exercise: Knee) muscle mass in normoxia, acute hypoxia (AH) ( ) and after 9 weeks of residence at 5260 m (CH). Reducing the size of the active muscle mass blunted by 62% the effect of hypoxia on in AH and abolished completely the effect of hypoxia on after altitude acclimatization. Acclimatization improved Bike peak exercise from 34 ± 1 in AH to 45 ± 1 mmHg in CH ( P < 0.05) and Knee from 38 ± 1 to 55 ± 2 mmHg ( P < 0.05). Peak cardiac output and leg blood flow were reduced in hypoxia only during Bike. Acute hypoxia resulted in reduction of systemic O2 delivery (46 and 21%) and leg O2 delivery (47 and 26%) during Bike and Knee, respectively, almost matching the corresponding reduction in . Altitude acclimatization restored fully peak systemic and leg O2 delivery in CH (2.69 ± 0.27 and 1.28 ± 0.11 l min−1, respectively) to sea level values (2.65 ± 0.15 and 1.16 ± 0.11 l min−1, respectively) during Knee, but not during Bike. During Knee in CH, leg oxygen delivery was similar to normoxia and, therefore, also in spite of a of 55 mmHg. Reducing the size of the active muscle mass improves pulmonary gas exchange during hypoxic exercise, attenuates the Bohr effect on oxygen uploading at the lungs and preserves sea level convective O2 transport to the active muscles. Thus, the altitude-acclimatized human has potentially a similar exercising capacity as at sea level when the exercise model allows for an adequate oxygen delivery (blood flow × ), with only a minor role of per se, when is more than 55 mmHg.
- Publication
Journal of Physiology, 2009, Vol 587, Issue 2, p477
- ISSN
0022-3751
- Publication type
Article
- DOI
10.1113/jphysiol.2008.162271