The effects of hypercapnia on metabolic responses to progressive exhaustive work

Altering CO2 storage has been shown to influence lactate metabolism. However, the metabolic effects on man during physical activity have not been well documented. Subjects (n = 8) performed a progressive bicycle test (beginning at 0 and increasing 30 W every 4 min to exhaustion) on two occasions (once inspiring compressed air and once 4% CO2 and 21% O2). The work time, peak Vo2, VCO2, and HR achieved were the same in the two trials for each subject. The VI was significantly (p less than or equal to 0.05) elevated throughout the CO2 work and the recovery. The O2 debt increased from a mean of 5.87 to 7.761 with CO2, although the difference was not significant. Blood lactate was lower (p less than or equal to 0.05) from the onset of the work and throughout both the exercise and the 30 min. recovery period. Peak lactate was decreased from a mean of 9.59 to 6.99mM.1(-1). The oxygen cost of the work was not altered but the blood lactate response to the 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.