Increase Characteristics of the Cumulated Excess-CO₂ and the Lactate Concentration During Exercise

The so-called excess-CO₂ in physical exertion results stoichiometrically directly from the quantity of protons bound in bicarbonate buffering. This situation is used in determining the ventilatory threshold (VT). However, the extent to which the degree and increase characteristics of excess-CO₂ can be used as an equivalent to blood lactate concentrations is uncertain. To investigate this relationship, 21 healthy men exercised on a cycle ergometer (starting at 50 watt, increases of 50 watt every 3 minutes) to subjective exhaustion. To evaluate the characteristics of this increase, a slope constant λ was calculated in relation to performance for both the blood lactate concentration (λ lactate) and the cumulated excess-CO₂ (λ CO₂excess). The start of the lactate increase (LT) and excess-CO₂ (VT) showed good intercorrelation (VT = 2.27 + 0.98 · LT; r = 0.914; P < 0.001). Mean λ lactate and λ CO₂ excess were of similar dimensions in all subjects (69.3 ± 39.8 watt vs. 80.11 ± 15.7 watt), but a minority of the subjects (n = 7) showed a considerably more gradual increase for the excess-CO₂ to the maximum. Since in addition there was no significant correlation between the absolute values for maximum lactate concentrations and the cumulative excess-CO₂, an interindividual prediction of lactate concentrations from the excess-CO₂ would be difficult. It is an open question, however, whether perhaps additional performance-limiting factors, such as the ventilation or the buffering capacity, may be included when measuring the excess-CO₂ so that this parameter could be more a measure for the formation rate of new lactate than the blood lactate concentration alone.

Exercise, testing, carbon dioxide, bicarbonate, ventilatory threshold, metabolic acidosis.

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