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Effect of carbohydrate feedings during high-intensity exercise
1Department of Kinesiology and Health Education, University of Texas, Austin 78712.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|October 1, 1988
Summary
Carbohydrate intake during prolonged exercise helps maintain blood glucose and allows trained cyclists to perform more work. Even with fueling, exercise intensity decreases later in prolonged, intense cycling sessions.
Area of Science:
- Exercise Physiology
- Sports Nutrition
Background:
- Prolonged exercise performance is limited by fuel availability and substrate utilization.
- Understanding carbohydrate oxidation limits is crucial for optimizing endurance exercise.
Purpose of the Study:
- To investigate the upper limits of steady-state exercise performance.
- To determine carbohydrate oxidation rates late in prolonged exercise.
- To assess the impact of carbohydrate feeding on endurance capacity.
Main Methods:
- Seven trained male cyclists performed prolonged cycling with alternating intensities (60-85% VO2max).
- Subjects received either a placebo or carbohydrate feedings throughout exercise.
- Plasma glucose, respiratory exchange ratio (R), and work performance were measured.
Main Results:
- Placebo group showed significant declines in plasma glucose and R, leading to fatigue.
- Carbohydrate feeding maintained higher plasma glucose levels and partially preserved carbohydrate oxidation.
- Carbohydrate intake increased work performance by 19% and allowed exercise at ~75% VO2max late in exercise.
Conclusions:
- Carbohydrate feedings are essential for sustaining performance during prolonged intense exercise.
- Trained cyclists can maintain exercise at ~75% VO2max and oxidize ~2 g/min of carbohydrate with feeding.
- Fuel availability significantly impacts endurance capacity and substrate utilization during extended exercise bouts.