This study investigated the effects of post-exercise rehydration with fluid alone or with a meal plus fluid. Eight healthy volunteers (five men, three women) were dehydrated by a mean of 2.1 (SEM 0.0)% of body mass by intermittent cycle exercise in a warm [34 (SEM 0) degrees C], humid [55 (SEM 1)% relative humidity] environment. Over 60 min beginning 30 min after exercise, the subjects ingested a commercially-available sports drink (21 mmol.l-1 Na+, 3.4 mmol.l-1 K+, 12 mmol.l-1 Cl-) on trials A and B: on trial C a standard meal [63 body mass (53% CHO, 28% fat, 19% protein; 0.118 mmol.kJ-1 Na+, 0.061 mmol.kJ-1 K+)] plus drink (1 mmol.l-1 Na+, 0.4 mmol.l-1 K+, 1 mmol.l-1 Cl-) were consumed. Water intake (in millilitres) was 150% of the mass loss (in grams). The trials took place after an overnight fast and were separated by seven days. Blood and urine samples were collected at intervals throughout the study. Blood was analysed for haematocrit, haemoglobin concentration, serum osmolality, Na+, K+ and Cl- concentrations and plasma angiotensin II concentration. Urine volume, osmolality and electrolyte concentrations were measured. Dehydration resulted in a mean 5.2 (SEM 1.3)% reduction in plasma volume. With the exception of serum osmolality, which was higher on trial B than A at the end of the rehydration period, no differences were recorded for any of the measured parameters between trials A and B. Cumulative urine output following rehydration was lower (P < 0.01) on trial C [median 665 (range 396-1190)ml] than on trial B [median 934 (range 550-1403)ml] which was not different (P = 0.44) from trial A [median 954 (range 474-1501)ml]. Less urine was produced over the 1-h period ending 2 h after rehydration on trial C than on B (P = 0.01). On trials A and B the subjects were in net negative fluid balance by 337 (range 779-minus 306) ml and 373 (range 680-minus 173)ml, respectively (P < 0.01): on trial C the subjects were no different from their initial euhydrated state [median minus 29 (range minus 421-137)ml] 6 h after the end of rehydration (P = 1.00). A larger fraction of total water intake was retained when the standard meal plus drink was consumed. This may have been due to the larger quantities of Na+ and K+ ingested with the meal [mean 63 (SEM 4) mmol Na+, 21.3 (SEM 1.3)mmol K+] than with the drink [mean 42(SEM 2)mmol Na+, 6.8 (SEM 0.4)mmol K+]. There was no difference between trials B and C in any of the measured blood parameters, but urinary Na+ and K+ excretion were both higher on trial C and B. These results suggest that post-exercise fluid replacement can be achieved by ingestion of water if consumed in sufficient volume together with a meal providing significant amounts of electrolytes.

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Maughan RJ, Leiper JB, Shirref...
Maughan RJ, Leiper JB, Shirreffs SM
Eur J Appl Physiol Occup Physi...
Eur J Appl Physiol Occup Physiol, 1996.