Oxygen Uptake during Maximal Work at Lowered and Raised Ambient Air Pressures

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Abstract
The maximal aerobic power (Vo2max) was measured in 12 subjects exercising on a bicycle ergometer breathing air at 0.68, 1.0 and 1.40 ATA ambient pressures. Seven of the subjects were also investigated at 2.0 and 3.0 ATA. Vo2max averaged 3.67 1·min‐1 STPD at 1.0 ATA and was reduced by 14 per cent at 0.68 ATA (p < 0.001), while at 1.40 ATA Vo2max was increased by 9 per cent (p < 0.001). The increased PIO2 at the two highest pressures did not result in any further improvement of vo2max compared to 1.40 ATA. At all pressures changes in endurance time parallelled those of Vo2max. Ventilation decreased markedly as ambient pressure increased with a concomitant rise of PACO2 up to a mean value of 43 mm Hg at 3.0 ATA as compared to 32 mm Hg at 1.0 ATA. It is concluded that moderate hyperoxia produced by increased ambient air pressure enhances circulatory transport of oxygen in maximal exercise, and that the working muscles have an aerobic potential exceeding what the circulation normally can offer.