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.