Effect of timing of carbohydrate ingestion on endurance exercise performance

Plasma glucose levels averaged 5.7 mmol.l-1 when carbohydrates were ingested throughout exercise, compared to 4.2 mmol.l-1 with no carbohydrate intake until late in exercise.

• Ingestion of a carbohydrate-electrolyte solution throughout exercise led to significantly higher plasma glucose levels compared to an artificially sweetened placebo.
• Plasma insulin levels were higher before performance testing with carbohydrates ingested during exercise compared to the control group.
• Work performed during the performance ride was significantly greater when carbohydrates were consumed throughout exercise (268 kJ) versus the control (242 kJ).
• Carbohydrate ingestion late in exercise did not enhance performance despite increased plasma glucose levels.
• Most subjects (seven out of eight) showed better performance when carbohydrates were ingested continuously during exercise.

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