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Related Experiment Videos

Exercise metabolism at different time intervals after a meal.

S J Montain1, M K Hopper, A R Coggan

  • 1Department of Kinesiology and Health, University of Texas, Austin 78712.

Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 1, 1991
PubMed
Summary

Eating a meal significantly impacts exercise metabolism. Carbohydrate oxidation is higher with shorter fasting periods, while blood glycerol increases with longer fasting. Plasma glucose drops during exercise, especially after shorter fasts.

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Area of Science:

  • Exercise Physiology
  • Sports Nutrition
  • Human Metabolism

Background:

  • Understanding the impact of meal timing on exercise metabolic responses is crucial for optimizing athletic performance and health.
  • Previous research indicates that nutrient availability influences substrate utilization during physical activity.

Purpose of the Study:

  • To investigate the duration of a meal's effect on the metabolic and hormonal responses during submaximal exercise.
  • To compare these responses between endurance-trained and untrained individuals.

Main Methods:

  • Nine endurance-trained and nine untrained subjects performed 30-minute cycling bouts at 70% of peak oxygen consumption (VO2 peak) at various time points (2, 4, 6, 8, 12 hours) after consuming a standardized high-carbohydrate meal (2 g/kg body weight).
  • Additional testing involved cycling at an intensity eliciting a respiratory exchange ratio (RER) of 0.94-0.95, four hours post-meal.

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  • Measurements included carbohydrate oxidation, blood glycerol concentration, and plasma glucose levels.

    • Main Results:

    • Carbohydrate oxidation during exercise was significantly elevated (13-15%) after 2 and 4 hours of fasting compared to 8 and 12 hours (P < 0.01).
    • Blood glycerol concentration during exercise showed a strong positive linear relationship with fasting duration (r = 0.99; P < 0.01).
    • Plasma glucose declined during exercise after 2 hours of fasting (17-21%; P < 0.01) and in trained subjects after 4 and 6 hours (15-25%; P < 0.05), but not in untrained subjects at these time points.

    Conclusions:

    • The metabolic effects of a carbohydrate-rich meal on exercise performance, particularly carbohydrate utilization and glucose regulation, persist for at least 4-6 hours.
    • Fasting duration significantly influences substrate oxidation and hormonal responses (e.g., glycerol release) during exercise.
    • Individual differences in training status may affect glucose homeostasis during prolonged exercise following a meal.