Exercise capacity in a child with McArdle disease.

We report the exercise capacity of an 8-year-old boy with clinical, histological, biochemical, and genetic evidence of McArdle disease. The patient presented with severe myalgia, proteinuria, hematuria, pyrexia, and elevated creatine kinase after swimming. After pre-exercise ingestion of sucrose, he performed treadmill exercise to symptom limitation. His peak oxygen uptake (18.8 mL/kg/min) and ventilatory threshold (16.0 mL/kg/min) were reduced by 40% and 20% compared with healthy age-matched and gender-matched controls. The results suggest that exercise capacity is reduced early in life in patients with McArdle disease and suggest the need for prophylactic exercise training (following pre-exercise feeding to prevent rhabdomyolysis) to minimize deconditioning.