Influence of carbohydrate ingestion on fuel substrate turnover and oxidation during prolonged exercise

Jun 1, 1994Journal of applied physiology (Bethesda, Md. : 1985)

How eating carbohydrates affects energy use and breakdown during long exercise

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Abstract

Ingesting a 10% carbohydrate drink at 500 ml/h led to a significant increase in total glucose appearance in endurance-trained cyclists during a 180-minute ride.

Total carbohydrate oxidation was similar between the carbohydrate drink and placebo groups.
Total glucose appearance increased significantly during exercise in both groups, but plateaued at 75 minutes in the carbohydrate drink group.
At the end of exercise, glucose appearance was significantly greater in the carbohydrate drink group compared to the placebo group.
Blood glucose oxidation also increased significantly and was higher in the carbohydrate drink group at the end of exercise.
Mean endogenous glucose appearance was significantly lower in the carbohydrate drink group throughout the trial.
Muscle glycogen utilization was identical in both groups and was higher during the first hour of exercise.

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This study examined effects of ingesting a 10% carbohydrate (CHO) drink (CI) or placebo (PI) at 500 ml/h on total (splanchnic) glucose appearance (endogenous+exogenous; Ra), blood glucose oxidation, and muscle glycogen utilization in 14 male endurance-trained cyclists who rode for 180 min at 70% of maximal O2 uptake after CHO loading [starting muscle glycogen 203 +/- 7 (SE) mmol/kg wet wt]. Total CHO oxidation was similar in CI and PI, but Ra increased significantly during the trial in both groups with CI reaching a plateau after 75 min. Ra was significantly greater in CI than in PI at the end of exercise. Blood glucose oxidation also increased significantly during the trial to a plateau in CI and was significantly higher in CI than in PI at the end of exercise. However, mean endogenous Ra was significantly lower in CI than in PI throughout exercise, as was oxidation of endogenous blood glucose, which remained almost constant in CI and reached 43 +/- 8 and 73 +/- 13 mumol.min-1.kg fat-free mass-1 in CI and PI, respectively, at the end of exercise. At 0.83 g/min of CHO ingestion, 0.77 +/- 0.03 g/min was oxidized. Muscle glycogen utilization was identical in both groups and was higher during the 1st h of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

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Influence of carbohydrate ingestion on fuel substrate turnover and oxidation during prolonged exercise

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