Metabolic alkalosis induced by pre-exercise ingestion of NaHCO3 does not modulate the slow component of VO2 kinetics in humans.

Seven healthy physically active nonsmoking men, aged 22.4 +/- (SD) 1.8 years performed two 6 min bouts of cycling at 40% VO2max (sub-lactate threshold/low power output exercise) and 87% VO2max (supra-lactate threshold/high power output exercise) at 70 rev.min-1, separated by 20 minutes rest, on two occasions: once as a control experiment (test C) and on a different day at approximately 1.5 h after ingestion of 250 mg (3 mmol).(kg body weight)-1 of NaHCO3 (test A). At the onset of low and high power output exercise performed after ingestion of NaHCO3, antecubital venous blood pH and HCO3- were significantly elevated (p < 0.05). Moreover, blood pH and HCO3-, tested at every minute of low and high power output exercise, was significantly higher (p < 0.05) in test A than in test C. No difference was found in plasma lactate concentration [La]pl during low power output exercise between A and C tests. In the terminal phase of the high power output exercise (87% VO2max) the level of [La]pl rose more rapidly in test A than in test C, reaching in the sixth minute of cycling 8.27 +/- 1.11 and 6.76 +/- 0.68 mmol.l-1 (p < 0.01) in test A and C, respectively. No significant differences were found in the rate of VO2 measured breath-by-breath between A and C tests, both during low and high power output exercise. The slow component of VO2 kinetics (expressed by difference between VO2 measured at the 6th minute of exercise minus the VO2 reached at the 3rd minute), occurring only during exercise corresponding to 87% VO2, was not significantly different in C and A tests (0.373 +/- 0.050 and 0.339 +/- 0.078 1 O2, respectively). The total VO2 consumed throughout the six minute cycling at power output of 40 and 87% VO2max performed in control conditions and after ingestion of NaHCO3 was not significantly different. We have demonstrated that significantly reduced exercise acidemia accompanied by a significantly elevated level of [La]pl accumulation, did not affect the slow component of the VO2 kinetics and the magnitude of oxygen uptake during exercise corresponding to 40 and 87% of VO2max.