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O2 max more than living and training in
normoxia
Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160-7401
The objective of these experiments was to determine
whether living and training in moderate hypoxia (MHx) confers an
advantage on maximal normoxic exercise capacity compared with living
and training in normoxia. Rats were acclimatized to and trained in MHx
[inspired PO2
(PIO2) = 110 Torr] for 10 wk (HTH).
Rats living in normoxia trained under normoxic conditions (NTN) at the
same absolute work rate: 30 m/min on a 10° incline, 1 h/day, 5 days/wk. At the end of training, rats exercised maximally in normoxia. Training increased maximal O2 consumption
(
O2 max) in NTN and HTH above normoxic
(NS) and hypoxic (HS) sedentary controls. However,
O2 max and O2 transport
variables were not significantly different between NTN and HTH:
O2 max 86.6 ± 1.5 vs. 86.8 ± 1.1 ml · min
1 · kg
1;
maximal cardiac output 456 ± 7 vs. 443 ± 12 ml · min
1 · kg
1; tissue
blood O2 delivery (cardiac output × arterial
O2 content) 95 ± 2 vs. 96 ± 2 ml · min
1 · kg
1; and
O2 extraction ratio (arteriovenous O2 content
difference/arterial O2 content) 0.91 ± 0.01 vs.
0.90 ± 0.01. Mean pulmonary arterial pressure (Ppa, mmHg) was
significantly higher in HS vs. NS (P < 0.05) at rest
(24.5 ± 0.8 vs. 18.1 ± 0.8) and during maximal exercise
(32.0 ± 0.9 vs. 23.8 ± 0.6). Training in MHx significantly attenuated the degree of pulmonary hypertension, with Ppa being significantly lower at rest (19.3 ± 0.8) and during maximal
exercise (29.2 ± 0.5) in HTH vs. HS. These data indicate that,
despite maintaining equal absolute training intensity levels,
acclimatization to and training in MHx does not confer significant
advantages over normoxic training. On the other hand, the pulmonary
hypertension associated with acclimatization to hypoxia is reduced with
hypoxic exercise training.
maximal O2 uptake; maximal exercise capacity; exercise training; hypoxic exercise; systemic O2 transport; tissue O2 delivery; tissue O2 extraction; hypoxic pulmonary vasoconstriction; hypoxic pulmonary hypertension
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