| This study was conducted to examine the effects of four different drink solutions on renal free water clearance, osmolal clearance, change in plasma volume, change in body weight, and change in extravascular water, in twelve healthy male and female participants. Pre-trial controls included no exercise >30 min in the previous 24 h, no caffeine or other diuretics in the previous 48 h, the ingestion of 40 mL water/kg body weight for each of the two preceding days, and a standard liquid breakfast the morning of the trial.;Subjects ingested either 1.2 g of glycerol/kg of body weight (BW) as a 40% solution followed by distilled water (GLY), a 6% carbohydrate solution (CHO), distilled water (DW), or a 100 mEq/L electrolyte solution (EL) in a repeated measures design during resting conditions. Total fluid intake was constant for all trials at 26 mL/kg of BW. Fluid ingestion began at time 0 and was repeated every 30 min for 2 h. Data on blood and urine osmolality, urine volume, hemoglobin, hematocrit, and body weight were collected every 30 minutes for 5 h.;Repeated measures ANOVA (4 x 10) were used to assess the effect of the four solutions over a time period of 5 h (10 time points) for each DV. Type I error rate was controlled by adjusting the alpha level using the Bonferroni method for the five interdependent variables (alpha = (0.05/5) = 0.01).;Results indicated that CHO was no better than DW for improving hydration. GLY was the most effective hydrating drink, inducing an approximate 1100 mL peak increase in body hydration, approximately 800 mL greater than DW or CHO, and 530 mL greater than EL. Furthermore, the duration of improved hydration was far longer with GLY than any other solution, remaining 370 mL greater than baseline at 5 h. Among the tested solutions, glycerol hyperhydration is clearly the most effective regimen for improving body hydration. The significantly reduced renal free water clearance during the GLY trial (--3.3 +/- 0.9 mL/min at 2.5 h) compared to all other trials (9.4 +/- 3.1, 3.8 +/- 2.1, and 9.0 +/- 2.1 mL/min for DW, EL and CHO at 2.5 h, respectively) supports previous theories of a renal mechanism for glycerol hyperhydation. |
