Glycerol hyperhydration fails to improve endurance performance and thermoregulation in humans in a warm humid environment

Abstract

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.

Human Water and Electrolyte Balance

“…68 Studies demonstrate that total body water can be increased by approximately 1.5 L and sustained for several hours with glycerol hyperhydration 66,68 ; however, glycerol provides no cardiovascular or thermoregulatory advantages over water ingestion alone when taken during exercise or heat stress. [68][69][70] The effects of glycerol hyperhydration on performance are mixed. Glycerol hyperhydration may [71][72][73] or may not 69,70 improve exercise performance.…”

“…[68][69][70] The effects of glycerol hyperhydration on performance are mixed. Glycerol hyperhydration may [71][72][73] or may not 69,70 improve exercise performance. Comparing study outcomes is complicated by differences in performance measures, climate, and the potentially confounding study design limitations.…”

Review of the Effects of Glycerol-Containing Hyperhydration Solutions on Gastric Emptying and Intestinal Absorption in Humans and in Rats

“…Studies have administered 20-29 ml of fluid/kg BW (1,400-2,200 ml), with an average corresponding to 24 ml/kg BW, or 1,700 ml (Anderson, Cotter, Garnham, Casley, & Febbraio, 2001;Coutts, Reaburn, Mummery, & Holmes, 2002;Freund et al, 1995;Goulet et al, 2006Goulet et al, , 2007Goulet et al, , 2008Griffin et al, 1999;Hitchins et al, 1999;Latzka et al, 1997Latzka et al, , 1998Lyons, Riedesel, Meuli, & Chick, 1990;Magal et al, 2003;Marino et al, 2003;Montner et al, 1996Montner et al, , 1999Nishijima et al, 2007;O'Brien, Freund, Young, & Sawka, 2005;Riedesel, Allen, Peake, & Al-Qattan, 1987;Wingo et al, 2004). As shown in Figure 1, there is a significant positive correlation between the quantity of fluid administered and the ability of GCHSs to increase fluid retention.…”

“…Some studies administered the glycerol as a bolus at the start of the ingestion protocol (Freund et al, 1995;Latzka et al, 1997Latzka et al, , 1998Lyons et al, 1990;Magal et al, 2003;Montner et al, 1996Montner et al, , 1999Nishijima et al, 2007;O'Brien et al, 2005;Riedesel et al, 1987), whereas others mixed it with the total fluid load to be ingested throughout the protocol (Anderson et al, 2001;Coutts et al, 2002;Goulet et al, 2006Goulet et al, , 2008Griffin et al, 1999;Hitchins et al, 1999;Marino et al, 2003;Nishijima et al, 2007;Wingo et al, 2004). A statistical analysis (independent t test) reveals that the fluid retention provided by both types of protocols does not differ significantly (Figure 2).…”

“…Some individual studies showed no effect of GIH on endurance performance compared with water-induced hyperhydration (Goulet, Robergs, Labrecque, Royer, & Dionne, 2006;Marino, Kay, & Cannon, 2003;Nishijima et al, 2007;Wingo et al, 2004). Moreover, the effects of GIH on cardiovascular and thermoregulatory functions during prolonged exercise are equivocal (Nelson & Robergs, 2007).…”