Increase characteristics of the cumulated excess-CO2 and the lactate concentration during exercise

The so-called excess-CO2 in physical exertion results stoichiometrically di rectly from the quantity of protons bound in bicarbonate buffering. This si tuation 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 i nvestigate 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 const ant lambda was calculated in relation to performance for both the blood lac tate concentration (lambda lactate) and the cumulated excess-CO2 (lambda CO (2)excess). The start of the lactate increase (LT) and excess-CO2 (VT) show ed good intercorrelation (VT = 2.27 + 0.98 . LT: r = 0.914; P < 0.001). Mea n lambda lactate and lambda CO2 excess were of similar dimensions in all su bjects (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 cum ulative excess-CO2, an interindividual prediction of lactate concentrations from the excess-CO2 would be difficult. It is an open question, however, w hether perhaps additional performance-limiting factors. such as the ventila tion or the buffering capacity, may be included when measuring the excess-C O2 so that this parameter could be more a measure for the formation rate of new lactate than the blood lactate concentration alone.