Foskett, A., Williams, C., Boobis, L., Txintzas, K. (2008). Carbohydrate availability and muscle energy metabolism during intermittent running. Medicine and Science in Sports and Exercise, 40, 96-103.

This study examined the influence of ingesting a carbohydrate-electrolyte solution on muscle glycogen use and intermittent running capacity after consumption of a carbohydrate-rich diet. Males (N = 6) performed two trials separated by 14 days. Ss consumed either a 6.4% carbohydrate-electrolyte solution or a placebo immediately before each trial (8 ml/kg) and at 15-minute intervals (3 ml/kg) during intermittent high-intensity running to fatigue performed after carbohydrate loading for two days. Muscle biopsy samples were obtained before exercise, after 90 minutes of exercise, and at fatigue.

Ss ran longer in the carbohydrate-electrolyte trial compared with the placebo trial. There were no statistically significant differences in muscle glycogen use for the first 90 minutes of exercise. However, there was a trend for a greater use in the placebo trial after 90 minutes than in the carbohydrate-electrolyte trial. Plasma glucose concentrations were higher at fatigue in the carbohydrate-electrolyte trial than in the placebo trial.

Implication. Carbohydrate-electrolyte ingestion improves endurance capacity during intermittent high-intensity running in Ss with high pre-exercise muscle glycogen concentrations. "The greater endurance capacity cannot be explained solely by differences in muscle glycogen, and it may actually be a consequence of the higher plasma glucose concentration towards the end of exercise that provided a sustained source of CHO for muscle metabolism and for the central nervous system".

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