Abnormal ventilation during exercise in McArdle's syndrome: modulation by substrate availability.

We evaluated ventilation during cycle exercise in four men lacking myophosphorylase. In submaximal exercise of similar relative intensity, ventilation was higher relative to oxygen uptake in McArdle patients than in normal men. The exercise ventilatory response returned to normal after glucose infusion, by fasting to increase free fatty acid availability or by combining fasting and submaximal exercise. Excessive ventilation in exercise was potentiated by inhibiting lipolysis with nicotinic acid. The excessive ventilatory effort and resultant respiratory alkalosis may contribute to exercise intolerance.