Lactic Acid and Acid-base Equilibrium

The classical view that lactic acid as final product of glycolysis is the only cause of the exercise-induced nonrespiratory acidosis is occasionally questioned. One group of authors even considers transposing of hydrogen on pyruvate during lactate formation as "metabolic buffering", the liberation of H+ occurring independently during splitting of ATP. In reality this is tightly coupled to glycolysis since ATP is immediately consumed. Other authors explain the acidosis by a reduction of the strong ion difference to which lactate only contribute, a part. Since. apart from lactate, strong ions are neither produced nor consumed but only shifted among compartments, these cannot cause acidosis in the whole body Finally, some authors conclude from larger changes in standard base excess than in blood lactate concentration that more H+ than lactate ions leave the muscle fibres. However, standard base excess is biassed during acidosis independent of origin because bicarbonate enters the interstitial fluid in exchange with Cl-. Thus all 3 theories are incorrect. Extracellular buffer capacity calculated from changes in pH and lactate concentration in plasma is greater during exercise than during recovery The main cause is a transient shrinking of the extracellular Volume by a water shift into muscle fibres, which increases buffer concentrations.