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Effects of preexercise feedings on endurance performance
Medicine and Science in Sports
|January 1, 1979
Summary
Consuming glucose before endurance exercise impairs performance by increasing carbohydrate use and hindering fat mobilization. Liquid meals did not affect endurance performance compared to water.
Area of Science:
- Exercise Physiology
- Sports Nutrition
- Human Metabolism
Background:
- Understanding the metabolic and performance effects of pre-exercise nutrition is crucial for athletes.
- Carbohydrate (CHO) ingestion before exercise can alter substrate utilization and endurance capacity.
- Previous research suggests potential negative impacts of CHO intake on lipid metabolism during exercise.
Purpose of the Study:
- To investigate the effects of pre-exercise glucose or a liquid meal on endurance performance and substrate utilization.
- To determine if pre-exercise feeding impacts exercise time to exhaustion at varying intensities.
- To examine serum glucose and free fatty acid (FFA) responses during exercise after different pre-exercise treatments.
Main Methods:
- Eight male and female students performed cycle ergometer tests to exhaustion at 80% and 100% of VO2max.
- Participants consumed either water (W), 75g glucose (G), or a liquid meal (M) 30-45 minutes prior to exercise.
- Blood samples were analyzed for serum glucose and FFA levels during exercise.
Main Results:
- Endurance performance time at 80% VO2max was significantly reduced (19%) with pre-exercise glucose (G) compared to water (W).
- No significant difference in performance was observed between the water (W) and liquid meal (M) trials at 80% VO2max.
- Pre-exercise feedings did not affect exercise duration at 100% VO2max, and serum glucose levels transiently declined then normalized during exercise in G and M trials.
Conclusions:
- Pre-exercise glucose ingestion impairs endurance performance at moderate intensity (80% VO2max) by increasing carbohydrate oxidation and impeding fat mobilization.
- Liquid meal ingestion did not negatively impact endurance performance, suggesting a different metabolic response compared to pure glucose.
- These findings highlight the importance of timing and composition of pre-exercise nutrition on substrate utilization and exercise capacity.
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