The effect of pre-exercise glucose ingestion on performance during prolonged swimming

The purpose of this study was to determine if pre-exercise glucose ingestion would improve distance swimming performance. Additionally, pre-exercise glucose was provided at 2 different feeding intervals to investigate the affects of the timing of administration. Ten male triathletes ((X) over bar +/- SD: age, 29.5 +/- 5.0 years; (V) over dotO(2peak), 48.8 +/- 3.2 ml (.) kg(-1) (.) min(-1)) swam 4000 in on 3 occasions following the consumption of either a 10% glucose solution 5 min prior to exercise (G(5)), a 10% glucose solution 35 min prior to exercise (G(35)), or a similar volume of placebo (PL). Despite a significant difference (p <.01) in blood glucose concentration prior to exercise ((X) over bar +/- SD in mmol (.) L-1: G(35) 8.4 +/- 1.1 vs. G(5) 5.2 +/- 0.5 or PL 5.3 +/- 0.4), no significant differences were observed in total time (X SD in minutes: G(35) 70.7 +/- 7.6, G(5) 70.1 +/- 7.6, PL 71.9 +/- 8.4), post-exercise blood glucose ((X) over bar +/- SD in mmol (.) L-1: G(35) 5.1 +/- 1.1, G(5) 5.1 +/- 0.9, PL 5.3 +/- 0.4), and average heartrate ((X) over bar +/- SD in bpm: G(35) 155.8 +/- 10.8, G(5) 153.6 +/- 12.6, PL 152.0 +/- 12.5; p >.05). While not reaching statistical significance, glucose feedings did result in improved individual performance times, ranging from 24 s to 5 min in 8 of the 10 subjects compared to the placebo. These results were found despite significant differences in blood glucose between trials immediately prior to exercise.