Gonzalez Javier T, Fuchs Cas J, Betts James A, van Loon Luc J C
Department for Health, University of Bath, Bath, United Kingdom; and
Department of Human Biology and Movement Sciences, NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Centre+, Maastricht, The Netherlands.
Am J Physiol Endocrinol Metab. 2016 Sep 1;311(3):E543-53. doi: 10.1152/ajpendo.00232.2016. Epub 2016 Jul 19.
Carbohydrate and fat are the main substrates utilized during prolonged endurance-type exercise. The relative contribution of each is determined primarily by the intensity and duration of exercise, along with individual training and nutritional status. During moderate- to high-intensity exercise, carbohydrate represents the main substrate source. Because endogenous carbohydrate stores (primarily in liver and muscle) are relatively small, endurance-type exercise performance/capacity is often limited by endogenous carbohydrate availability. Much exercise metabolism research to date has focused on muscle glycogen utilization, with little attention paid to the contribution of liver glycogen. (13)C magnetic resonance spectroscopy permits direct, noninvasive measurements of liver glycogen content and has increased understanding of the relevance of liver glycogen during exercise. In contrast to muscle, endurance-trained athletes do not exhibit elevated basal liver glycogen concentrations. However, there is evidence that liver glycogenolysis may be lower in endurance-trained athletes compared with untrained controls during moderate- to high-intensity exercise. Therefore, liver glycogen sparing in an endurance-trained state may account partly for training-induced performance/capacity adaptations during prolonged (>90 min) exercise. Ingestion of carbohydrate at a relatively high rate (>1.5 g/min) can prevent liver glycogen depletion during moderate-intensity exercise independent of the type of carbohydrate (e.g., glucose vs. sucrose) ingested. To minimize gastrointestinal discomfort, it is recommended to ingest specific combinations or types of carbohydrates (glucose plus fructose and/or sucrose). By coingesting glucose with either galactose or fructose, postexercise liver glycogen repletion rates can be doubled. There are currently no guidelines for carbohydrate ingestion to maximize liver glycogen repletion.
碳水化合物和脂肪是长时间耐力型运动中利用的主要底物。每种底物的相对贡献主要由运动强度和持续时间以及个人训练和营养状况决定。在中高强度运动中，碳水化合物是主要的底物来源。由于内源性碳水化合物储备（主要存在于肝脏和肌肉中）相对较少，耐力型运动表现/能力往往受到内源性碳水化合物可用性的限制。迄今为止，许多运动代谢研究都集中在肌肉糖原的利用上，而对肝糖原的贡献关注较少。碳-13磁共振波谱法可以直接、无创地测量肝糖原含量，并增加了对运动期间肝糖原相关性的理解。与肌肉不同，经过耐力训练的运动员基础肝糖原浓度并未升高。然而，有证据表明，在中高强度运动期间，与未经训练的对照组相比，耐力训练运动员的肝糖原分解可能较低。因此，在耐力训练状态下节省肝糖原可能部分解释了长时间（>90分钟）运动期间训练引起的表现/能力适应。在中等强度运动期间，以相对较高的速率（>1.5克/分钟）摄入碳水化合物可以防止肝糖原耗尽，而与摄入的碳水化合物类型（例如葡萄糖与蔗糖）无关。为了尽量减少胃肠道不适，建议摄入特定组合或类型的碳水化合物（葡萄糖加果糖和/或蔗糖）。通过将葡萄糖与半乳糖或果糖同时摄入，可以使运动后肝糖原的补充率提高一倍。目前尚无关于碳水化合物摄入以最大化肝糖原补充的指南。
