Effect of water ingestion on endurance capacity during prolonged running

This study examined the influence of water ingestion on endurance capacity during submaximal treadmill running. Four men and four women with a mean (+/-S.E.) age of 21.4 +/- 0.7 years, height of 169 +/- 2 cm, body mass of 63.1 +/- 2.9 kg and VO2 max of 51.1 +/- 1.8 ml kg-1 min-1, performed two randomly assigned treadmill runs at 70% VO2 max to exhaustion. No fluid was ingested during one trial (NF-trial), whereas a single water bolus of 3.0 ml kg-1 body mass was ingested immediately pre-exercise and serial feedings of 2.0 ml kg-1 body mass were ingested every 15 min during exercise in a fluid replacement trial (FR-trial). Run time for the NF-trial was 77.7 +/- 7.7 min, compared to 103 +/- 12.4 min for the FR-trial (P < 0.01). Body mass (corrected for water ingestion) decreased by 2.0 +/- 0.2% in the NF-trial and 2.7 +/- 0.2% in the FR-trial (P < 0.01), while plasma volume decreased by 1.1 +/- 1.1% and 3.5 +/- 1.1% in the two trials respectively (N.S.). However, these apparent differences in circulatory volume were not associated with differences in rectal temperature. Respiratory exchange ratios indicated increased carbohydrate metabolism (73% vs 64% of total energy expenditure) and suppressed fat metabolism after 75 min of exercise in the NF-trial compared with the FR-trial (NF-trial, 0.90 +/- 0.01; FR-trial, 0.86 +/- 0.03; P < 0.01). Blood glucose concentrations were similar in both trials, while blood lactate concentrations were higher in the NF-trial at the end of exercise (4.83 +/- 0.34 vs 4.18 +/- 0.38 mM; P < 0.05). In summary, water ingestion during prolonged running improved endurance capacity.