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 () level. Patients with McArdle disease ( = 8) and healthy controls ( = 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 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 electromyographic activity during submaximal exercise, all < 0.05) and an impaired endurance exercise capacity (–51% ventilatory threshold and –55% peak power output, both < 0.001). Regardless of the CHO dose ( < 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 ventilatory threshold (+27%, = 0.010) and peak power output (+18%, = 0.007). 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 are dose dependent.

中文翻译：

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运动前碳水化合物在肌糖原不可用情况下的剂量反应效应：来自麦卡德尔病的见解

本研究旨在确定不同碳水化合物 (CHO) 剂量对麦卡德尔病患者运动能力的影响（“运动不耐受”的范例，其特征是完全肌糖原不可用），并确定较高的外源性葡萄糖水平是否会影响代谢反应麦卡德尔肌细胞 () 水平。麦卡德尔病患者 ( = 8) 和健康对照 ( = 9) 接受 12 分钟次最大循环恒定负荷试验，然后在摄入无热量安慰剂 15 分钟后进行最大斜坡测试。在随机、双盲、交叉设计中，患者在食用 75 克或 150 克 CHO（葡萄糖：果糖 = 2：1）后重复测试。评估心肺、生化、知觉和肌电图 (EMG) 变量。此外，还研究了以增加的葡萄糖浓度（0.35、1.00、4.50 和 10.00 g/L）培养的野生型和 McArdle 小鼠肌管的葡萄糖摄取和乳酸外观。与对照组相比，患者表现出“典型的”二次风现象（之前出现不成比例的心动过速、肌痛和次最大运动期间过度的肌电活动，全部 < 0.05）和耐力运动能力受损（通气阈值 –51% 和通气阈值 –55%）峰值功率输出，均< 0.001)。无论 CHO 剂量如何（与安慰剂相比，两种剂量均< 0.05），CHO 摄入会增加患者的血糖和乳酸水平，降低脂肪氧化率，并减弱患者的复吸。然而，只有较高剂量才会增加通气阈值（+27%，= 0.010）和峰值功率输出（+18%，= 0.007）。分析显示，野生型肌管中的乳酸水平随葡萄糖浓度没有差异，而在 McArdle 肌管中观察到剂量反应效应。摄入 CHO 对麦卡德尔病的运动能力产生有益影响，麦卡德尔病是一种与总肌糖原不可用相关的疾病。其中一些益处是剂量依赖性的。