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1 Department of Kinesiology, University of Waterloo, Waterloo, Ontario N2L 3G1; 2 Ottawa Heart Institute, University of Ottawa, Ottawa, Ontario K1Y 4E9; 3 Division of Sports Medicine, University of British Columbia, British Columbia, Canada V6T 1Z3; and 4 Department of Anesthesiology, University of Washington, Seattle, Washington 98124
To investigate the hypothesis that respiratory
gas exchange and, in particular, the O2 consumption
(
O2) response to exercise is altered
after a 21-day expedition to 6,194 m, five male climbers (age 28.2 ± 2 yr; weight 76.9 ± 4.3 kg; means ± SE) performed a
progressive and prolonged two-step cycle test both before and 3-4
days after return to sea level. During both exercise tests, a
depression (P < 0.05) in
O2 (l/min) and an increase
(P < 0.05) in minute ventilation (E
BTPS; l/min) and respiratory exchange ratio were observed after
the expedition. These changes occurred in the absence of changes in
CO2 production (l/min). During steady-state submaximal
exercise, net efficiency, calculated from the rates of the mechanical
power output to the energy expended (O2)
above that measured at rest, increased (P < 0.05) from
25.9 ± 1.6 to 31.3 ± 1.3% at the lighter power output and
from 24.4 ± 1.3 to 29.5 ± 1.5% at the heavy power output.
These changes were accompanied by a 4.5% reduction (P < 0.05) in peak O2 (3.99 ± 0.17 vs. 3.81 ± 0.18 l/min). After the expedition, an increase
(P < 0.05) in hemoglobin concentration (15.0 ± 0.49 vs. 15.8 ± 0.41 g/100 ml) was found. It is concluded that,
because resting O2 was unchanged, net
efficiency is enhanced during submaximal exercise after a mountaineering expedition when the exercise is performed soon after
return to sea level conditions.
exercise; aerobic; O2 consumption; hypoxia
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