THE EFFECT OF VOLUME INGESTED ON REHYDRATION AND GASTRIC-EMPTYING FOLLOWING EXERCISE-INDUCED DEHYDRATION

The purpose of this study was to examine the effects of different drin k volumes on rehydration, gastric emptying, and markers of fluid balan ce following exercise-induced dehydration. Nine male subjects (27.3 +/ - 5.47 yr of age, 77.8 +/- 7.9 kg) exercised for 90 min (or until 2.5% of initial body weight was lost) on a cycle ergometer in a hot enviro nment (30 degrees C with 60% RH). Following exercise, subjects were mo ved to a neutral environment (23 degrees C 50% RH) and rested for 30 m in prior to beginning a 3-h rehydration period. During rehydration, su bjects were serially fed with an electrolyte solution (14.98 mmol.l(-1 ) Na+, 13.51 mmol.l(-1) Cl-, and 7.95 mmol.l(-1) K+) every 30 min with either 100% or 150% of the fluid lost during exercise. Gastric conten ts were determined every 15 min using double sampling. Blood samples, urine samples, and body weights were taken before and after exercise a nd at 1-h intervals throughout rehydration. Blood samples were analyze d for percent change in plasma volume, electrolyte concentration, aldo sterone levels, and renin activity. Urine electrolyte concentrations w ere also measured. The final percent rehydration was 48.11 and 67.90 f or the 100% and 150% conditions, respectively. During rehydration, the subjects emptied 98.9 and 86.0% of the fluid ingested, and the % empt ied and used for weight gain at the end of rehydration was 55.1 and 54 .6 for the 100% and 150% trials, respectively. Urine production was si gnificantly higher in the 150 compared with the 100% condition while r enin and aldosterone levels did not differ significantly. These result s suggest gastric emptying did not represent a limiting factor in rehy dration. Furthermore, although there was a greater % rehydration obser ved in the 150% condition, this was attained via relatively large gast ric fluid volumes, with concomitantly large urine volumes; thus, force d fluid intake with a dilute, low sodium rehydration solution was not an effective method of rapid rehydration and may be detrimental to sub sequent performance. Additionally, the large urine productions observe d in the last hour of rehydration for both trials indicate that fluid retention hormones were not maintained at an adequate level to stimula te rapid rehydration in a short amount of time following dehydration.