title: Plasma glucose kinetics during prolonged exercise in trained humans when fed carbohydrate.
abstract: Nine endurance-trained men exercised on a cycle ergometer at approximately 68% peak O2 uptake to the point of volitional fatigue [232 +/- 14 (SE) min] while ingesting an 8% carbohydrate solution to determine how high glucose disposal could increase under physiological conditions. Plasma glucose kinetics were measured using a primed, continuous infusion of [6,6-2H]glucose and the appearance of ingested glucose, assessed from [3-3H]glucose that had been added to the carbohydrate drink. Plasma glucose was increased (P < 0.05) after 30 min of exercise but thereafter remained at the preexercise level. Glucose appearance rate (R(a)) increased throughout exercise, reaching its peak value of 118 +/- 7 micromol. kg(-1). min(-1) at fatigue, whereas gut R(a) increased continuously during exercise, peaking at 105 +/- 10 micromol. kg(-1). min(-1) at the point of fatigue. In contrast, liver glucose output never rose above resting levels at any time during exercise. Glucose disposal (R(d)) increased throughout exercise, reaching a peak value of 118 +/- 7 micromol. kg(-1). min(-1) at fatigue. If we assume 95% oxidation of glucose R(d), estimated exogenous glucose oxidation at fatigue was 1.36 +/- 0.08 g/min. The results of this study demonstrate that glucose uptake increases continuously during prolonged, strenuous exercise when carbohydrate is ingested and does not appear to limit exercise performance.
authors.affiliation: Department of Physiology, The University of Melbourne, Parkville, Victoria 3052, Australia.
authors.forename: Damien J
authors.initials: DJ
authors.lastname: Angus
authors.forename: Mark A
authors.initials: MA
authors.lastname: Febbraio
authors.forename: Mark
authors.initials: M
authors.lastname: Hargreaves
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000032:analysis*; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D015444:Exercise / Q000502:physiology*; D005221:Fatigue / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008297:Male; D010806:Physical Education and Training; D010807:Physical Endurance; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005947:Glucose