Effect of oral sucrose shortly before exercise on work capacity in McArdle disease

Background: Oral sucrose (75 g) ingested 40 minutes before exercise improves exercise tolerance in McArdle disease. Objective: To determine whether a lower dose of sucrose administered closer in time to exercise could have a similar beneficial effect on exercise capacity in patients with McArdle disease. Design: Placebo-controlled crossover. Setting: Neuromuscular Research Unit at the Department of Neurology, Rigshospitalet, Copenhagen, Denmark. Patients: Six patients with biochemically and genetically diagnosed McArdle disease. Interventions: On separate days, the patients were tested after ingestion of either 75 g of sucrose or a placebo 40 minutes before exercise, or 37 g of sucrose or a placebo 5 minutes before exercise. Patients were blinded to test substances. Main Outcome Measures: Treatment effectiveness was assessed by monitoring heart rate and perceived exertion during exercise. Results: Both sucrose treatments dramatically improved exercise tolerance, compared with the placebo. The low-dose, 5-minute sucrose trial had a more sustained effect on exercise capacity than the 40-minute trial. The more sustained effect was probably related to more continuous glucose uptake from the intestine and correspondingly higher circulating glucose levels later during exercise. Conclusions: This study shows that 37 g of sucrose ingested shortly before exercise has a marked and prolonged effect on exercise tolerance in patients with McArdle disease. This treatment is more convenient for the patients and saves more calories than the currently recommended sucrose treatment.