Acid-base balance during repeated bouts of exercise: influence of HCO3

Abstract

Ten men and one woman were studied before, during, and following five 1-min cycling bouts (100% VO2 max) 1 h after consuming either 0.2 g/kg B.W. of NaHCO3 or a placebo drink (NaCl). The fifth exercise bout was performed until exhaustion and the time recorded to judge the effects of the NaHCO3 drink on performance. Blood samples taken from a forearm vein revealed that the intake of NaHCO3 increased resting pH (7.34 to 7.41), HCO3 (27.5 to 31.0 mM), and base excess (1.1 to 4.6 mM). During and following the exercise, blood pH and HCO3 were always higher (P less than 0.05) in the NaHCO3 than placebo trial. Performance times during the fifth cycling bout averaged 113.5 (SE +/- 12.4) and 160.8 (SE +/- 19.1) s in the NaCl and NaHCO3 trials, respectively. This 42% difference between the means was significant at the 0.01 level. The blood hydrogen ion to lactic acid ratios (nM/mM) measured between each exercise bout and during recovery from the exhaustive fifth bout suggests that the enhanced performance during the NaHCO3 trial was the result of greater buffer capacity. Thigh muscle (vastus lateralis) pH measured immediately before the fifth cycling bout in four of the subjects revealed that the working muscles were less acid in the NaHCO3 trial (pH = 6.81) than during the NaCl treatment (pH = 6.73). Thus, the alkalizing influence of oral HCO3 supports the concept that the hydrogen ion concentration in blood and muscle has a direct influence on performance during repeated, supramaximal exercise.