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Fuel utilisation during prolonged low-to-moderate intensity exercise when ingesting water or carbohydrate
L H Rauch1, A N Bosch, T D Noakes
1Bioenergetics of Exercise Research Unit of The Medical Research Council, Department of Physiology, The University of Cape Town Medical School, Observatory 7925, South Africa.
Pflugers Archiv : European Journal of Physiology
|October 1, 1995
Summary
Carbohydrate (CHO) ingestion is crucial for sustaining prolonged, low-to-moderate intensity exercise. Supplementing with CHO during exercise prevents fatigue and shifts energy production from fat to glucose oxidation.
Area of Science:
- Exercise Physiology
- Sports Nutrition
- Metabolic Studies
Background:
- Previous research examined carbohydrate (CHO) effects on glucose kinetics during high-intensity exercise (70% VO2 max).
- This study investigates CHO ingestion's impact on glucose metabolism in heavier cyclists during prolonged, lower-intensity exercise (55% VO2 max).
Purpose of the Study:
- To determine if carbohydrate ingestion sustains prolonged exercise at 55% VO2 max.
- To analyze the effects of CHO on glucose kinetics, substrate oxidation, and exercise performance in heavier cyclists.
Main Methods:
- Cyclists (n=6 per group) underwent 3-hour exercise trials at a fixed absolute oxygen uptake (VO2).
- Participants received either flavored water (H2O) or a glucose polymer solution (10 g/100 ml) at 600 ml/h.
- Glucose kinetics were measured using a 2-3H-glucose tracer, and substrate oxidation was assessed.
Main Results:
- Subjects ingesting only water (H2O) fatigued after 2.5 hours, experiencing declining glucose levels and plateaued oxidation rates.
- Carbohydrate ingestion (CHO) allowed all subjects to complete the 3-hour exercise duration.
- CHO intake increased total glucose appearance (Ra), plasma glucose concentration ([Glu]), and glucose oxidation (Rox), while suppressing endogenous glucose production and reducing relative fat oxidation.
Conclusions:
- Carbohydrate ingestion is essential for maintaining performance during prolonged exercise at intensities below 60% of VO2 max.
- CHO supplementation shifts substrate utilization towards carbohydrates, sparing fat oxidation at lower exercise intensities.
- Adequate CHO intake is necessary to prevent fatigue and support sustained energy production during endurance activities.