Available online 27 November 2023

In patients with McArdle disease, which is characterized by complete muscle glycogen unavailability, pre-exercise CHO intake exerted beneficial effects on exercise tolerance and maximal exercise capacity.

Although not all outcomes followed the same pattern, CHO benefits on maximal exercise capacity showed a dose–response association.

A dose–response effect of exogenous glucose on lactate production was observed in McArdle mouse myotubes.

This study aimed to determine the effect of different carbohydrate (CHO) doses on exercise capacity in patients with McArdle disease—the paradigm of “exercise intolerance”, characterized by complete muscle glycogen unavailability—and to determine whether higher exogenous glucose levels affect metabolic responses at the McArdle muscle cell (in vitro) level.

Patients with McArdle disease (n = 8) and healthy controls (n = 9) underwent a 12-min submaximal cycling constant-load bout followed by a maximal ramp test 15 min after ingesting a non-caloric placebo. In a randomized, double-blinded, cross-over design, patients repeated the tests after consuming either 75 g or 150 g of CHO (glucose:fructose, 2:1). Cardiorespiratory, biochemical, perceptual, and electromyographic (EMG) variables were assessed. Additionally, glucose uptake and lactate appearance were studied in vitro in wild-type and McArdle mouse myotubes cultured with increasing glucose concentrations (0.35, 1.00, 4.50, and 10.00 g/L).

Compared with controls, patients showed the “classical” second-wind phenomenon (after prior disproportionate tachycardia, myalgia, and excess EMG activity during submaximal exercise, all p < 0.05) and an impaired endurance exercise capacity (–51% ventilatory threshold (VT) and –55% peak power output (PPO), both p < 0.001). Regardless of the CHO dose (p < 0.05 for both doses compared with the placebo), CHO intake increased blood glucose and lactate levels, decreased fat oxidation rates, and attenuated the second wind in the patients. However, only the higher dose increased VT (+27%, p = 0.010) and PPO (+18%, p = 0.007). In vitro analyses revealed no differences in lactate levels across glucose concentrations in wild-type myotubes, whereas a dose–response effect was observed in McArdle myotubes.

CHO intake exerts beneficial effects on exercise capacity in McArdle disease, a condition associated with total muscle glycogen unavailability. Some of these benefits were dose-dependent.

Endurance

Glycogen storage disease

Glycogenosis

Nutrition

Supplement

© 2023 Published by Elsevier B.V. on behalf of Shanghai University of Sport.