INDIVIDUAL DIFFERENCES IN RESPIRATORY GAS EXCHANGE DURING RECOVERY FROM MODERATE EXERCISE

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Abstract
The thermal conductivity method of gas analysis for continual and simultaneous analyses of O2 and CO2 in expired air was used for measuring O2 consumption and CO2 elimination of humans during and after exercise. Metabolic gas exchange curves during and after various types of moderate exercises were studied for individual differences. The recovery phase from simple step-up exercises was found to be practical for this purpose. The gas exchange recovery curves are exponential, the half-time constants of which are functions of recovery rates. Reliability and variability of the time constants of recovery from a mild step-up exercise were detd. by tests and retests on 38 [male] subjects of various ages. The reliabilities of the CO2 and O2 time constants are 0.74 and 0.55, respectively, with standard errors of measurements being [plus or minus]12% and [plus or minus]15% of the means. The avg. of the CO2 half-time recovery constants (43.0 secs.) of 36 subjects is 40% more than the avg. O2 time constants (31.3 secs.); thus the rate of payment of the O2 debt is more rapid than elimination of the corresponding excess CO2. The O2 and CO2 recovery constants, however, are not independently variable as the correlation between them is 0.84. Different intensities and durations of moderate exercise have little or no effect on the recovery constants which permits comparison of recovery rates between individuals who perform varying degrees of work. With increasing age of subjects there is increased slowness of CO2 elimination during recovery; the CO2 half-time recovery constants of 60 yr. old subjects are nearly double those of 20 yr. old subjects. The O2 recovery constants are apparently less affected by age, differences appearing mainly between the very youngest and oldest subjects. The age effect accounts to a large extent for the inter-individual differences in recovery rates. In any age group, the more physically fit individuals tend to have lower recovery constants and, in addition, rigorous training of one subject brought about a 16% reduction in the CO2 and O2 recovery constants. The possibility is considered that the limiting factors in the rate of O2 consumption and CO2 elimination during recovery are circulatory in nature.