Effects of pH on maximal power output and fatigue during short-term dynamic exercise

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Abstract
Six healthy [human] subjects performed 4 exercise studies in random order on separate days: a control study, metabolic acidosis induced by NH4Cl, metabolic alkalosis induced by NaHCO3- and respiratory acidosis induced by 5% CO2 inhalation. The subjects exerted maximal force on the pedals of a constant-velocity cycle ergometer at 100 rpm for 30 s; torque was measured and power calculated. Arterialized venous blood was sampled and plasma lactate concentrations was measured immediately after and at 2-min intervals for 10 min following exercise. Although maximal peak power and total work, for the 30-s test, were lower in the 2 acidosis conditions, this effect was not statistically significant. Plasma lactate 30 s postexercise was lower in metabolic acidosis (2.8 .+-. 1.6 mmol .cntdot. 1-1) (mean .+-. SD) and respiratory acidosis (1.5 .+-. 0.8 mmol .cntdot. 1-1) than in placebo conditions (5.9 .+-. 3.3 mmol .cntdot. l-1) and metabolic alkalosis (7.8 .+-. 4.2 mmol .cntdot. 1-1). These differences were maintained but lessened during 10 min of recovery. In contrast to previous studies, which showed a marked reduction in endurance time during sustained heavy exercise, reductions in blood pH are associated with only small reductions in the total work performed in 30 s of maximal exercise. A delayed and smaller accumulation of lactate in plasma was observed following exercise during acidosis.