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Oxidation of carbohydrate ingested during prolonged endurance exercise.
J A Hawley1, S C Dennis, T D Noakes
1Department of Physiology, University of Cape Town Medical School, Observatory, South Africa.
Sports Medicine (Auckland, N.Z.)
|July 1, 1992
Summary
Consuming carbohydrates (CHO) during exercise delays fatigue by preventing low blood sugar and fueling muscles. Research confirms CHO intake enhances endurance, leading to studies on optimal CHO types for athletes.
Area of Science:
- Exercise Physiology
- Sports Nutrition
- Metabolic Research
Background:
- Early 20th-century studies linked high carbohydrate (CHO) diets and glucose ingestion to delayed fatigue and prevention of hypoglycemia during exercise.
- Interest in CHO ingestion during exercise declined for decades, with focus shifting to pre-exercise glycogen storage and hydration.
- Concerns arose in the 1970s that CHO solutions delayed gastric emptying, potentially worsening dehydration, leading to athlete discouragement.
Purpose of the Study:
- To re-evaluate the effects of carbohydrate (CHO) ingestion during prolonged exercise on fatigue onset and muscle glycogen utilization.
- To investigate the oxidation rates of ingested carbohydrates, particularly glucose, during exercise.
- To address the historical skepticism regarding CHO intake during exercise and identify optimal CHO sources for performance.
Main Methods:
- Utilized muscle biopsy techniques (reintroduced in the 1960s) to assess muscle glycogen levels during exercise.
- Employed stable 13C and radioactive 14C isotope tracers since the 1970s to quantify ingested CHO oxidation during exercise.
- Analyzed respiratory gas exchange measurements for earlier estimates of CHO utilization.
Main Results:
- Muscle glycogen depletion correlates with fatigue development during prolonged exercise.
- Ingestion of carbohydrates during prolonged exercise has been re-established to delay fatigue.
- Significant oxidation of ingested glucose occurs during exercise, with peak rates observed 75-90 minutes post-ingestion, independent of feeding timing.
Conclusions:
- Carbohydrate ingestion during exercise is a viable strategy to delay fatigue and enhance endurance performance.
- The study of CHO oxidation during exercise has advanced significantly with isotopic techniques, confirming the utility of ingested fuels.
- Further research is warranted to determine the optimal types and timing of carbohydrate ingestion for athletes.