Preexercise metabolic alkalosis induced via bicarbonate ingestion accelerates V̇o2 kinetics at the onset of a high-power-output exercise in humans

Abstract

The present study investigated the effect of preexercise metabolic alkalosis on the primary component of oxygen uptake (V̇o2) kinetics, characterized by τ1. Seven healthy physically active nonsmoking men, aged 22.4 ± 1.8 (mean ± SD) yr, maximum V̇o2 (V̇o2 max) 50.4 ± 4 ml·min−1·kg−1, performed two bouts of cycling, corresponding to 40 and 87% of V̇o2 max, lasting 6 min each, separated by a 20-min pause, once as a control study and a few days later at ∼90 min after ingestion of 3 mmol/kg body wt of NaHCO3. Blood samples for measurements of bicarbonate concentration and hydrogen ion concentration were taken from antecubital vein via catheter. Pulmonary V̇o2 was measured continuously breath by breath. The values of τ1 were calculated by using six various approaches published in the literature. Preexercise level of bicarbonate concentration after ingestion of NaHCO3 was significantly elevated ( P < 0.01) compared with the control study (28.96 ± 2.11 vs. 24.84 ± 1.18 mmol/l; P < 0.01), and [H+] was significantly ( P < 0.01) reduced (42.79 ± 3.38 nmol/l vs. 46.44 ± 3.51 nmol/l). This shift ( P < 0.01) was also present during both bouts of exercise. During cycling at 40% of V̇o2 max, no significant effect of the preexercise alkalosis on the magnitude of τ1 was found. However, during cycling at 87% of V̇o2 max, the τ1 calculated by all six approaches was significantly ( P < 0.05) reduced, compared with the control study. The τ1 calculated as in Borrani et al. (Borrani F, Candau R, Millet GY, Perrey S, Fuchsloscher J, and Rouillon JD. J Appl Physiol 90: 2212–2220, 2001) was reduced on average by 7.9 ± 2.6 s, which was significantly different from zero with both the Student's t-test ( P = 0.011) and the Wilcoxon's signed-ranks test ( P = 0.014).