It is well-established that oral
sucrose ingested shortly before exercise improves early exercise tolerance in individuals with
McArdle disease. This is by supplying blood-borne
glucose for muscle metabolism to compensate for the blocked glycogenolysis. The present study investigated if individuals with
McArdle disease could benefit further from repeated
sucrose ingestion during prolonged exercise. In this double-blind, placebo-controlled, cross-over study, the participants were randomized to ingest either
sucrose or placebo first and subsequently the opposite on two separate days. The participants ingested the drink 10 min before and thrice (after 10, 25, and 40 min) during a 60-min submaximal exercise test on a cycle ergometer. The primary outcome was exercise capacity as indicated by heart rate (HR) and perceived exertion (PE) responses to exercise. Secondary outcomes included changes in blood metabolites,
insulin and
carbohydrate, and
fatty acid oxidation rates during exercise. Nine participants with
McArdle disease were included in the study. We confirmed improvement of exercise capacity with oral
sucrose vs. placebo during early exercise (pre-second wind) indicated by lower peak HR and PE (p < 0.02). We found no further beneficial effect with repeated
sucrose versus placebo ingestion during prolonged exercise, as indicated by no difference in HR or PE post-second wind (p > 0.05).
Glucose,
lactate,
insulin, and
carbohydrate oxidation rates increased, and
fatty acid oxidation decreased with
sucrose versus placebo (p ≤ 0.0002). We can conclude that repeated
sucrose ingestion is not recommended during prolonged exercise. This finding can prevent excessive caloric intake and reduce the risk of
obesity and
insulin resistance.