Effectiveness of glycerol as a rehydrating agent

On two occasions, 8 male subjects completed a dehydration protocol, immedia tely followed by a 180-min rehydration protocol, then a subsequent exercise bout. During each dehydration session, subjects lost 3.1 +/- 0.4% body wei ght (BW)following discontinuous exercise in the heat (40 degreesC, 33% rh). During the first 30 min of rehydration, subjects ingested either 1.0-g gly cerol . kg body weight(-1) + 30% of the total rehydration water volume (GLY ), or 30% of the total rehydration water volume without glycerol (CON). The five remaining ingestions (every 30 min) were equal to 14% of the remainin g fluid volume and were identical in nature. Fluid volume ingested equaled fluid volume lost during dehydration. Following the 180 min rehydration per iod, subjects cycled (similar to 50% (V) over dot (2peak)) in the heat (40 degreesC, 33% rh) until volitional exhaustion. Three observations were made : (a) Following glycerol-induced rehydration, time to volitional exhaustion was greater during the subsequent exercise bout in the heat (CON: 38.0 +/- 2.0, GLY 42.8 +/- 1.0 min, p < .05); (b) glycerol-induced rehydration sign ificantly increased plasma volume restoration within 60 min and at the end of the 180-min rehydration period; and (c) total urine volume was lower and percent rehydration was greater following GLY, but neither was significant ly different.