POSTEXERCISE REHYDRATION IN MAN - EFFECTS OF ELECTROLYTE ADDITION TO INGESTED FLUIDS

This study examined the effects on water balance of adding electrolyte s to fluids ingested after exercise-induced dehydration. Eight healthy male volunteers were dehydrated by approximately 2% of body mass by i ntermittent cycle exercise. Over a 30-min period after exercise, subje cts ingested one of the four test drinks of a volume equivalent to the ir body mass loss. Drink A was a 90mmol.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 m mol.l(-1) sodium chloride and 25 mmol.l(-1) potassium chloride. Treatm ent order was randomised. Blood and urine samples were obtained at int ervals throughout the study; subjects remained fasted throughout. Plas ma volume increased to the same extent after the rehydration period on all treatments. Serum electrolyte (Na+, K+ and Cl-) concentrations fe ll 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 follo wing the trial, subjects were in greater net negative fluid balance [m ean (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 a t any time between the three electrolyte-containing solutions in urine output or net fluid balance. One hour after the end of the rehydratio n period, urine osmolality hand fallen, with a significant treatment e ffect (P=0.016); urine osmolality was lowest after ingestion of drink A, On the morning after the test, subjects were in greater net negativ e sodium balance (P<0.001) after trials A and C than after trials B an d D. Negative potassium balance was greater (P<0.001) after trials A a nd B than after C and D. Chloride balance was positive after drink D a nd a smaller negative balance (P<0.001) was observed after drink B tha n after A and C. These results suggest that although the measured bloo d parameters were similar for all trials, better whole body water and electrolyte balance resulted from the ingestion of electrolyte-contain ing drinks. There appeared, however, to be no additive effect of inclu ding both sodium and potassium under the conditions of this experiment .