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Reduced oxidation rates of ingested glucose during prolonged exercise with low endogenous CHO availability
A E Jeukendrup1, L B Borghouts, W H Saris
1Department of Human Biology, University Maastricht, The Netherlands. A.Jeukendrup@HB.RuLimburg.NL
Journal of Applied Physiology (Bethesda, Md. : 1985)
|November 1, 1996
Summary
Lowering endogenous carbohydrate stores before exercise significantly reduces the body's ability to oxidize ingested glucose during moderate-intensity exercise. This impacts overall fuel utilization for endurance activities.
Area of Science:
- Exercise Physiology
- Nutritional Biochemistry
- Sports Science
Background:
- Endogenous carbohydrate (glycogen) availability is a key determinant of exercise performance.
- Understanding how glycogen status affects the metabolism of ingested carbohydrates is crucial for optimizing fueling strategies.
Purpose of the Study:
- To investigate the impact of pre-exercise endogenous carbohydrate (CHO) levels on the oxidation of ingested glucose during moderate-intensity exercise.
- To quantify the effect of low versus moderate-to-high glycogen stores on exogenous glucose utilization.
Main Methods:
- Seven well-trained cyclists completed 120-minute cycling trials at 57% maximal O2 consumption.
- Pre-exercise glycogen was manipulated through glycogen-lowering exercise and CHO restriction (low-glycogen) or CHO loading (moderate-to-high-glycogen).
- 13C-labeled glucose was ingested, and exogenous glucose oxidation was calculated using 13C enrichment in breath CO2.
Main Results:
- Total carbohydrate oxidation was significantly lower in the low-glycogen trial compared to the moderate-to-high-glycogen trial.
- Exogenous glucose oxidation was 28% lower, and maximal exogenous oxidation rates were reduced in the low-glycogen condition.
- This reduced exogenous glucose utilization was associated with higher plasma free fatty acid levels and lower insulin concentrations.
Conclusions:
- Glycogen-lowering exercise combined with carbohydrate restriction prior to exercise impairs the oxidation of ingested glucose during moderate-intensity exercise.
- These findings highlight the importance of adequate pre-exercise carbohydrate availability for maximizing exogenous fuel utilization and potentially sustaining endurance performance.