Effects of bicarbonate ingestion on the respiratory compensation threshold and maximal exercise performance.

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Abstract
Six males performed cycle ergometer exercise on two occasions in random order. Each exercise was preceded by a 2-h period in which matched capsules were administered orally, containing either starch (C) or NaHCO3 (E) in a dose of 0.2 g .cntdot. kg-1 body wt; pre-exercise blood pH and [HCO3-] were 7.34 .+-. 0.01 and 23.7 .+-. 0.5 mM (mean .+-. S.E.) for the C study, and 7.41 .+-. 0.01 and 28.6 .+-. 1.3 mM for the E study (p < 0.001 and p < 0.01, respectively). Exercise was continuous and maintained for 10 min at 40% of maximal oxygen uptake (40% .ovrhdot.VO2max), followed by 15 min at 12 W above the respiratory compensation threshold ([+RCT]) which was determined by the increase of the ventilatory equivalent for carbon dioxide (.ovrhdot.VE .cntdot. .ovrhdot.VCO2-1) and for as long as possible at 95% .ovrhdot.V02max. Endurance time at 95% .ovrhdot.VO2max was significantly longer in E than in C (2.98 .+-. 0.64 min vs. 2.00 .+-. 0.44 min, p < 0.05). The rate of increase in arterialized venous lactate (LA) was higher in E than in C from rest to exercise at [+ RCT], while there was no significant difference in the hydrogen ions ([H+]). Consequently, [H+] .cntdot. LA-1 (nM .cntdot. mM-1) was significantly lower in E than in C. The change of .ovrhdot.VE .cntdot. .ovrhdot.VCO2-1 was shifted downwarnd in E compared to C during exercise with the lowest value being observed at the same excersie stage. These results suggest th the respiratory responses to exercise are not affected by the higher level of [HCO3-] induced by NaHCO3 ingestion, and appear to reflect the net change of plasma [HCO3-] or [H+]. Also, induced metabolic acidosis has little effect on [H+] appearance in blood.
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