Effect of fluid intake volume on 2-h running performances in a 25 degrees C environment

Med Sci Sports Exerc. 2000 Oct;32(10):1783-9. doi: 10.1097/00005768-200010000-00019.


Purpose: In this study, we examined the effects of greater than ad libitum rates of fluid intake on 2-h running performances.

Methods: Eight male distance runners performed three runs on a treadmill at 65% of peak oxygen uptake (VO2peak) for 90 min and then ran "as far as possible" in 30 min in an air temperature of 25 degrees C, a relative humidity of 55% and a wind speed of 13-15 km x h(-1). During the runs, the subjects drank a 6.9% carbohydrate (CHO)-electrolyte solution either ad libitum or in set volumes of 150 or 350 mL x 70 kg(-1) body mass (approximately 130 or 300 mL) every 15-20 min.

Results: Higher (approximately 0.9 vs 0.4 L x h(-1)) rates of fluid intake in the 350 mL x 70 kg(-1) trial than in the other trials had minimal effects on the subjects' urine production (approximately 0.1 L x h(-1)), sweat rates (approximately 1.2 L x h(-1)), declines in plasma volume (approximately 8%), and rises in serum osmolality (approximately 5 mosmol x L(-1)) and Na+ concentrations (approximately 7 mEq x L(-1)). A greater (approximately 1.0 vs 0.5 g x min(-1)) rate of CHO ingestion in the 350 mL x 70 kg(-1) trial than in the other trials also did not affect plasma concentrations of glucose (> or = 5 mmol x L(-1)) and lactate (approximately 3 mmol x L(-1)) during the performance runs. In all three performance runs, increases in running speeds from approximately 14 to 15-16 km x h(-1) and rises in exercise intensities from approximately 65% to 75% of VO2peak elevated plasma lactate concentrations from approximately 1.5 to 3 mmol x L(-1) and accelerated CHO oxidation from approximately 13 to 15 mmol x min(-1). The only effect of the additional intake of approximately 1.0 L of fluid in the 350 mL x 70 kg(-1) trial was to produce such severe gastrointestinal discomfort that two of the eight subjects failed to complete their performance runs.

Conclusion: Greater rates of fluid ingestion had no measurable effects on plasma volume and osmolality and did not improve 2-h running performances in a 25 degrees C environment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Abdominal Pain / etiology
  • Adult
  • Blood Glucose / metabolism
  • Drinking*
  • Humans
  • Lactic Acid / blood
  • Male
  • Plasma Volume
  • Potassium / blood
  • Rehydration Solutions / adverse effects
  • Rehydration Solutions / therapeutic use*
  • Running / physiology*
  • Sodium / blood
  • Temperature
  • Time Factors
  • Water-Electrolyte Balance / physiology


  • Blood Glucose
  • Rehydration Solutions
  • Lactic Acid
  • Sodium
  • Potassium