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Related Experiment Videos

Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate.

E F Coyle, A R Coggan, M K Hemmert

    Journal of Applied Physiology (Bethesda, Md. : 1985)
    |July 1, 1986
    PubMed
    Summary

    Carbohydrate intake during prolonged exercise delays fatigue in endurance athletes by maintaining high rates of carbohydrate oxidation from non-muscle glycogen sources. This strategy supports extended performance without depleting muscle glycogen stores.

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    Area of Science:

    • Sports Science
    • Exercise Physiology
    • Nutritional Biochemistry

    Background:

    • Muscle glycogen is a primary fuel source during prolonged strenuous exercise.
    • Fatigue during endurance events is often linked to glycogen depletion and reduced carbohydrate oxidation.

    Purpose of the Study:

    • To investigate if delaying fatigue with carbohydrate intake during prolonged exercise correlates with slower muscle glycogen depletion.
    • To examine substrate utilization and performance in endurance athletes under different feeding conditions.

    Main Methods:

    • Seven endurance-trained cyclists completed two trials: one with a placebo (water) and one with carbohydrate (glucose polymer) ingestion.
    • Exercise intensity was maintained at approximately 71% of maximal oxygen consumption (VO2max) until fatigue.

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  • Muscle glycogen depletion, plasma glucose levels, and respiratory exchange ratio (R) were monitored.

    • Main Results:

    • Carbohydrate ingestion extended exercise duration by approximately one hour compared to placebo (4.02 vs. 3.02 hours).
    • Plasma glucose was maintained with carbohydrate feeding, whereas it declined significantly with placebo.
    • While muscle glycogen depletion rates were similar for the first 3 hours, the additional exercise hour with carbohydrate involved minimal muscle glycogen utilization.

    Conclusions:

    • Carbohydrate feeding postpones fatigue in endurance athletes by enabling sustained high rates of carbohydrate oxidation from sources other than muscle glycogen.
    • Endurance athletes can utilize alternative carbohydrate sources to maintain performance during the latter stages of prolonged exercise.
    • This strategy allows for extended exercise duration without compromising overall carbohydrate oxidation or relying heavily on muscle glycogen.