AGREEMENT OF LACTATE INCREASE AND CUMULATED CO2 EXCESS IN THE MULTI-STAGE TEST 1520

Abstract

The socalled CO2 excess (CE) is the stoichiometric direct result of buffering of lactic acid by bicarbonate. According to Stringer et al. (1995, Eur J Appl Physiol 72, 25-31), the increase in lactic acid in blood under constant, high-intensity exercise can be depicted by the CE. In order to test the hypothesis of the degree to which agreement between lactate increase and CE can be seen when applied to an incremental test protocol, we examined 47 male athletes with former ergometer experience in a multi-level bicycle ergometer test (initial exercise 50 watts, with increases of 50 watts every 3 minutes). To check the reproducibility, 14 tests were repeated after an interval of 10 days. The lactate concentration in blood was determined in capillary blood at the end of each exercise level. Respiratory gas measurement was performed using respiratory mass-spectrometry with breath-by-breath analysis. The CE was calculated from the overproportional increase in the ratio between ˙VCO2 and ˙VO2 and plotted cumulatively against the power output. The increase in lactate concentration was presented as a curve after interpolation with an equalizing spline (seeFigure). The onset of lactate increase (“lactate threshold”, LT) showed a high agreement with the onset of increase in CE(CET; r=0.94; p<0.001; y=1.3-1.06·x). Both thresholds were detected observer-independently by computer routines. No agreement could be found between the maximum lactate concentration and the maximum cumulative CE. The reproducibility of the CET seemed higher than for the LT (r=0.96 vs. r=0.84). The results show that the two methods are interchangeable with respect to determination of the LT. The cumulative extent of the CE is probably, however, more dependent on the individual extent of the athlete's buffering capacity than on the lactate concentration.