Acid-base regulation during exercise and recovery in humans

Arterial pH, PCO2, standard bicarbonate, lactate, and ventilation were measured with a high sampling density during rest, exercise, and recovery in normal subjects performing upright cycle ergometer exercise. Three 6-min constant-work exercise tests (moderate, heavy, and very heavy) were performed by each subject. We found a small respiratory acidosis during the moderate-intensity exercise and an early respiratory acidosis followed by a metabolic acidosis for the heavy- and very-heavy-intensity exercise. During recovery, arterial pH rapidly returned to the preexercise value for the moderate-intensity work. However, arterial pH decreased further during the first 2 min of recovery for the heavy- and very-heavy-intensity work, before a slower return toward the resting values. We conclude that arterial acidosis is the consistent arterial pH reaction for moderate-, heavy-, and very-heavy-intensity cycle ergometer exercise in humans and that this acidosis is blunted but not eliminated by the ventilatory response. During recovery, the return to resting arterial pH and PCO2 and standard bicarbonate appears to be determined by the rate of lactate decline.