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.