Effect of pH on Muscle Glycolysis during Exercise

Abstract

1. Five males were studied on three occasions, after oral administration of CaCO₃ (control), NH₄Cl (acidosis) and NaHCO₃ (alkalosis), in a dose of 0.3 g/kg, taken over a 3 h period at rest. The subjects then exercised on a cycle ergometer for 20 min at 33% maximal oxygen uptake (Vo₂ max.), followed by 20 min at 66% and at 95% Vo₂ max. until exhaustion. 2. Endurance at 95% Vo₂ max. was longest with alkalosis (5.44 ± 1.05 min), shortest with acidosis (3.13 ± 0.97 min) and intermediate in the control study (4.56 ± 1.31 min); venous blood pH at exhaustion was 7.33 ± 0.02 (mean ±1 sem), 7.13 ± 0.02 and 7.26 ± 0.02 respectively. 3. Concentrations of plasma lactate at exhaustion were 7.10 ± 0.8 mmol/l 4.0 ± 0.5 and 7.9 ± 0.9 mmol/l in the control, acidosis and alkalosis studies respectively. 4. Muscle lactate increased most from rest to exhaustion with alkalosis to 17.1 ± 2.5 μmol/g and least with acidosis to 12.2 ± 1.4 μmol/g. Muscle glycogen depletion was comparable in control and alkalosis studies. 5. The lower plasma lactate concentration during exercise in acidosis compared with control and alkalosis appears to be due to an inhibition of muscle glycolysis combined with a reduction in lactate efflux from muscle.