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% V̇O₂ 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 < 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.

Key words

blood pH - muscle pH - lactic acid - bicarbonate