Preexercise carbohydrate ingestion, glucose kinetics, and muscle glycogen use: effect of the glycemic index

• Published in: Journal of applied physiology (1985) Vol. 89; no. 5; pp. 1845 - 1851
• Main Authors: Febbraio, Mark A, Keenan, Justin, Angus, Damien J, Campbell, Shannon E, Garnham, Andrew P
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.11.2000; American Physiological Society
• Subjects: Adult; Biological and medical sciences; Biopsy; Carbohydrates; Effects; Energy Metabolism - physiology; Exercise; Exercise - physiology; Fundamental and applied biological sciences. Psychology; Glucose; Glucose - administration & dosage; Glucose - pharmacokinetics; Glycogen - metabolism; Humans; Insulin - blood; Male; Metabolisms and neurohumoral controls; Muscle, Skeletal - metabolism; Oxygen Consumption - physiology; Time Factors; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Physical exercise; Human; Physical performance; Glycogen; Glucose; Striated muscle; Feeding; Ingestion; Food intake; Carbohydrate; Glycogenolysis; Kinetics; Glycemia
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.2000.89.5.1845

1  Exercise Physiology and Metabolism Laboratory, Department of Physiology, The University of Melbourne, Parkville 3052; 2  Department of Human Biology and Movement Science, Royal Melbourne Institute of Technology, Bundoora 3083; and 3  School of Health Sciences, Deakin University, Burwood 3125, Australia Eight trained men cycled at 70% peak oxygen uptake for 120 min followed by a 30-min performance cycle after ingesting either a high-glycemic index (HGI), low-glycemic index (LGI), or placebo (Con) meal 30 min before exercise. Ingestion of HGI resulted in an elevated ( P  < 0.01) blood glucose concentration compared with LGI and Con. At the onset of exercise, blood glucose fell ( P  <   0.05) such that it was lower ( P  < 0.05) in HGI compared with LGI and Con at 15 and 30 min during exercise. Plasma insulin concentration was higher ( P  < 0.01) throughout the rest period after ingestion of HGI compared with LGI and Con. Plasma free fatty acid concentrations were lower ( P  < 0.05) throughout exercise in HGI compared with LGI and Con. The rates of [6,6- 2 H]glucose appearance and disappearance were higher ( P  < 0.05) at rest after ingestion and throughout exercise in HGI compared with LGI and Con. Carbohydrate oxidation was higher ( P  < 0.05) throughout exercise, whereas glycogen use tended ( P  = 0.07) to be higher in HGI compared with LGI and Con. No differences were observed in work output during the performance cycle when comparing the three trials. These results demonstrate that preexercise carbohydrate feeding with a HGI, but not a LGI, meal augments carbohydrate utilization during exercise but does not effect exercise performance. glucose uptake; glucose production; preexercise feeding; glycogenolysis