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/1 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 mumol/g and least with
acidosis to 12.2 +/- 1.4 mumol/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.