Maximal Work Performance at Raised Air and Helium‐Oxygen Pressures

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Abstract
To study the influence of increased air pressure and gas density on maximal work performance, cardiorespiratory measurements were made on 8 subjects who performed maximal exercise until exhaustion on a cycle ergometer while breathing air at ambient pressures of 1.0 (control), 3.0, and 6.0 ATA, and a mixture of 79 % helium and 21 % oxygen (He‐O2) at 3.0 ATA (same density as air at 1.0 ATA). Exposure to air at 3.0 and 6.0 ATA caused no consistent changes in maximal oxygen uptake (Vo2max), peak blood lactate (LA), or endurance time, whereas pulmonary ventilation (VE) and carbon dioxide elimination (Vco2) decreased significantly with a consequent rise of end‐tidal PCo2 from 35 mm Hg at 1.0 ATA, to 56 mm Hg at 6.0 ATA. Maximal heart rate (HRmax) decreased from a mean control value of 192 beats‐min‐1to 183 beats‐min‐1at 6.0 ATA. With exposure to He‐O2 at 3.0 ATA, as compared to control, Vo2max and endurance time increased by 13 % and 14 %, respectively, whereas VE and HRmax decreased, Vco2 and LA remained unchanged, and end‐tidal Pco2 rose to 39 mm Hg. It is concluded that the beneficial effect that hyperoxia exerts on Vo2max and endurance time at normal gas density is offset when the gas density is high enough to cause ventilatory impairment with concomitant CO2 retention. The results also suggest that maximal work performance was more closely related to the LA concentration than to the Pco2 or pH levels existing in the working muscles at the point of exhaustion.