Glycerol hyperhydration fails to improve endurance performance and thermoregulation in humans in a warm humid environment.Pflugers Arch. 2003 Jul; 446(4):455-62.PA
It is equivocal whether glycerol hyperhydration improves exercise performance and thermoregulation in the heat. The purpose of this study was to compare the effectiveness of glycerol with water hyperhydration, using a reliable, self-paced variable-intensity cycling protocol under hot, humid conditions. Seven moderately-to-well trained subjects ingested either a solution consisting of 1.2 g kg(-1) body mass (BM) glycerol mixed with 21 ml kg(-1) BM flavoured water (GLY) or placebo (PL), which was flavoured water of equal volume to the GLY trial, 2.5 h before exercise. Following hyperhydration, subjects undertook a self-paced, variable-intensity cycling protocol designed to simulate racing, with the aim being to cycle as great a distance as possible over 60 min. There were no differences in total distance cycled between conditions (29.7+/-5.7 km for PL, 28.9+/-5.7 km for GLY). Power output was not different at any time between conditions. Terminal rectal temperatures were 39.0+/-0.5 degrees C for PL and 38.8+/-0.7 degrees C for GLY and were not significantly different. Heart rate was significantly higher for GLY only during the high-intensity efforts. The sweat rate for GLY was 1.72+/-0.28 l h(-1) (P<0.01) compared with 1.15+/-0.29 l h(-1) for PL. It is concluded that glycerol hyperhydration has no significant advantage over water hyperhydration on performance or thermoregulation during a 1-h, variable-intensity exercise performance.