Increases in submaximal cycling efficiency mediated by altitude acclimatization

Abstract

To investigate the hypothesis that respiratory gas exchange and, in particular, the O2 consumption (V˙o 2) 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) inV˙o 2 (l/min) and an increase ( P < 0.05) in minute ventilation (V˙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 (V˙o 2) 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 V˙o 2 (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 V˙o 2 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.