Effects of Bicarbonate Ingestion on the Respiratory Compensation Threshold and Maximal Exercise Performance

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 a 0.2g·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±1.3mM 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% VǙO2max), 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 (V˙e·V˙CO2−1), and for as long as possible at 95% V˙O2max. Endurance time at 95% V˙O2max 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+]·LA−1 (nm·mm−1) was significantly lower in E than in C. The change of V˙e·V˙CO2−1 was shifted downward in E compared to C during exercise with the lowest value being observed at the same exercise stage. These results suggest that 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. © 1989, PHYSIOLOGICAL SOCIETY OF JAPAN. All rights reserved.