Plasma glucose kinetics during prolonged exercise in trained humans when fed carbohydrate

Damien J. Angus, Mark A. Febbraio, Mark Hargreaves

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Nine endurance-trained men exercised on a cycle ergometer at ∼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 (Ra) increased throughout exercise, reaching its peak value of 118 ± 7 μmol·kg-1·min-1 at fatigue, whereas gut Ra increased continuously during exercise, peaking at 105 ± 10 μmol·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 (Rd) increased throughout exercise, reaching a peak value of 118 ± 7 μmol·kg-1·min-1 at fatigue. If we assume 95% oxidation of glucose Rd, 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.

Original languageEnglish
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number3 46-3
Publication statusPublished - 1 Sept 2002
Externally publishedYes


  • Glucose production
  • Glucose uptake
  • Glycogenolysis

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