Md. Koskolou et al., HYPOXIA AND THE CARDIOVASCULAR-RESPONSE TO DYNAMIC KNEE-EXTENSOR EXERCISE, American journal of physiology. Heart and circulatory physiology, 41(6), 1997, pp. 2655-2663
Hypoxia affects O-2 transport and aerobic exercise capacity. In two pr
evious studies, conflicting results have been reported regarding wheth
er O-2 delivery to the muscle is increased with hypoxia or whether the
re is a more efficient O-2 extraction to allow for compensation of the
decreased O-2 availability at submaximal and maximal exercise. To rec
oncile this discrepancy, we measured limb blood flow (LBF), cardiac ou
tput, and O-2 uptake during two-legged knee-extensor exercise in eight
healthy young men. They completed studies at rest, at two submaximal
workloads, and at peak effort under normoxia (inspired O-2 fraction 0.
21) and two levels of hypoxia (inspired O-2 fractions 0.16 and 0.11).
During submaximal exercise, LBF increased in hypoxia and compensated f
or the decrement in arterial O-2 content. At peak effort, however, our
subjects did not achieve a higher cardiac output or LBF. Thus O-2 del
ivery was not maintained and peak power output and leg O-2 uptake were
reduced proportionately. These data are consistent then with the find
ings of an increased LBF to compensate for hypoxemia at submaximal exe
rcise, but no such increase occurs at peak effort despite substantial
cardiac capacity for an elevation in LBF.