Post-exercise rehydration in man: effects of electrolyte addition to ingested fluids

  • R. J. Maughan
  • J. H. Owen
  • S. M. Shirreffs
  • J. B. Leiper
Original Articles

Abstract

This study examined the effects on water balance of adding electrolytes to fluids ingested after exercise-induced dehydration. Eight healthy male volunteers were dehydrated by approximately 2% of body mass by intermittent cycle exercise. Over a 30-min period after exercise, subjects ingested one of the four test drinks of a volume equivalent to their body mass loss. Drink A was a 90 mmol·l−1 glucose solution; drink B contained 60 mmol·l−1 sodium chloride; drink C contained 25 mmol·l−1 potassium chloride; drink D contained 90 mmol·l−1 glucose, 60 mmol·l−1 sodium chloride and 25 mmol·l−1 potassium chloride. Treatment order was randomised. Blood and urine samples were obtained at intervals throughout the study; subjects remained fasted throughout. Plasma volume increased to the same extent after the rehydration period on all treatments. Serum electrolyte (Na+, K+ and Cl) concentrations fell initially after rehydration before returning to their pre-exercise levels. Cumulative urine output was greater after ingestion of drink A than after ingestion of any of the other drinks. On the morning following the trial, subjects were in greater net negative fluid balance [mean (SEM);P<0.02] on trial A [745 (130) ml] than on trials B [405 (51) ml], C [467 (87) ml] or D [407 (34) ml]. There were no differences at any time between the three electrolyte-containing solutions in urine output or net fluid balance. One hour after the end of the rehydration period, urine osmolality had fallen, with a significant treatment effect (P=0.016); urine osmolality was lowest after ingestion of drink A. On the morning after the test, subjects were in greater net negative sodium balance (P<0.001) after trials A and C than after trials B and D. Negative potassium balance was greater (P<0.001) after trials A and B than after C and D. Chloride balance was positive after drink D and a smaller negative balance (P<0.001) was observed after drink B than after A and C. These results suggest that although the measured blood parameters were similar for all trials, better whole body water and electrolyte balance resulted from the ingestion of electrolyte-containing drinks. There appeared, however, to be no additive effect of including both sodium and potassium under the conditions of this experiment.

Key words

Dehydration Rehydration Fluid balance Exercise Electrolyte balance 

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Copyright information

© Springer-Verlag 1994

Authors and Affiliations

  • R. J. Maughan
    • 1
  • J. H. Owen
    • 1
  • S. M. Shirreffs
    • 1
  • J. B. Leiper
    • 1
  1. 1.University Medical School, ForesterhillAberdeenScotland

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