The effects of hypercapnia on metabolic responses to progressive exhaustive work

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Abstract
Altering CO2 storage influences lactate metabolism. The metabolic effects on man during physical activity were not well documented. Subjects (8) performed a progressive bicycle test (beginning at 0 and increasing 30 W every 4 min to exhaustion) on 2 occasions (once inspiring compressed air and once 4% CO2 and 21% O2). The work time, peak .ovrhdot.VO2 [O2 consumption], VCO2 [lung volume of CO2] and HR [heart rate] achieved were the same in the 2 trials for each subject. The VI [inspired volume] was significantly (P .ltoreq. 0.05) elevated throughout the CO2 work and the recovery. The O2 debt increased from a mean of 5.87-7.76 with CO2, although the difference was not significant. Blood lactate was lower (P .ltoreq. 0.05) from the onset of the work and throughout the exercise and the 30 min recovery period. Peak lactate was decreased from a mean of 9.59-6.99mM. The O2 cost of the work was not altered but the blood lactate response to the activity was significantly depressed. The reduction in lactate activity was significantly depressed. The reduction in lactate could be due to glycolytic inhibition and enhanced fat metabolism. The data support, but do not prove, this hypothesis.

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