Smith, G. J., Rhodes, E. C., & Langill, R. H. (2002). The effect of pre-exercise glucose ingestion on performance during prolonged swimming. International Journal of Sport Nutrition and Exercise Metabolism, 12, 136-144.

Male triathletes (N = 10) served as Ss to determine if pre-exercise glucose ingestion would improve distance swimming performance. Ss swam 4,000 m on three occasions. One trial consisted of placebo at 35 minutes, followed by a 10% glucose (5 ml/kgbw) solution at 5 minutes before the exercise. Another was a 10% glucose solution 35 minutes before exercise followed by a placebo at 5 minutes. The third trial consisted of a placebo at both 35 and 5 minutes.

No significant differences between group times and heart rates were revealed. Some individuals did respond with improved times in the direction that one would expect. Blood glucose levels were significantly higher following the 35-min administration than in the other two conditions. Post-exercise blood glucose and lactate levels did not differ between the three trials.

Implication. Some Ss responded positively to glucose feeding before a 4,000-m distance swimming time trial. However, there was no statistically significant effect on group performance. It is possible that only some swimmers will benefit from pre-exercise glucose ingestion.

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