A Meta-Analysis of the Effects of Glycerol-Induced Hyperhydration on Fluid Retention and Endurance Performance

Abstract

The authors determined, through a meta-analytic approach, whether glycerolinduced hyperhydration (GIH) enhances fluid retention and increases endurance performance (EP) significantly more than water-induced hyperhydration (WIH). Collectively, studies administered 23.9 ± 2.7 mL of fluid/kg body weight (BW) with 1.1 ± 0.2 g glycerol/kg BW, and hyperhydration was measured 136 ± 15 min after its onset. Compared with WIH, GIH increased fluid retention by 7.7 ± 2.8 mL/kg BW (P < 0.01; pooled effect size [PES]: 1.64 ± 0.80, P < 0.01, N = 14). The use of GIH was associated with an improvement in EP of 2.62% ± 1.60% (P = 0.047; PES: 0.35 ± 0.13, P = 0.014, N = 4). Unarguably, GIH significantly enhances fluid retention better than WIH. Because of the dearth of data, the effect of GIH on EP must be further investigated before more definitive conclusions can be drawn as to its ergogenic property.Key Words: overhydration, dehydration, exercise capacity, ergogenic aid, cardiovascular function, thermoregulatory function On exercise initiation the metabolism increases severalfold to match the increased energy demand of the working muscles. Human beings are relatively inefficient at producing movements-only 25% of the energy produced is directly used for locomotion while the remainder 75% is lost as heat (9). Hence, core temperature increases during exercise (56). To avoid hyperthermia, the body eliminates most of the excess body heat through the production and evaporation of sweat, although convection and radiation can participate to the process to a much lesser extent. The rate of sweat production during exercise depends on a variety of factors such as exercise intensity (85), environmental conditions (85), training state (10), degree of heat acclimatization (14), and clothing worn (87). In temperate (20-25 °C) (4,11,18,29,30) and hot (>30 °C) (38, 59, 60) ambient conditions sweat rates in Scholarly reviewS

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

“…Four studies with no exercise period examined the effect of GIH on total body water during time periods ranging from 210 to 300 min (Freund et al, 1995;Griffin et al, 1999;O'Brien et al, 2005;Riedesel et al, 1987). The average length of a typical GIH protocol is 136 min (Goulet et al, 2007). There is a trend toward an inverse relationship between the effectiveness of GCHSs in increasing fluid retention and protocol length (r = -.38, p = .09, n = 22 studies).…”

“…This might be because of the lack of variation in the amount of glycerol administered by studies. Nevertheless, Goulet et al (2007) indicated that the ideal quantity of glycerol ingested to maximize fluid retention is 1-1.2 g/kg BW.…”

“…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.…”

“…Hence, the efficacy of GIH is maximized when the volume of fluid administered is in the upper range of the quantities normally provided. Goulet et al (2007) indicated that a fluid dose of 26 ml/kg BW should maximize fluid retention.…”

“…In a recent meta-analysis (Goulet, Aubertin-Leheudre, Plante, & Dionne, 2007), glycerol-induced hyperhydration (GIH) was demonstrated to significantly enhance fluid retention and power output during prolonged exercise by 50% and 2.6%, respectively, compared with water-induced hyperhydration. Moreover, it has recently been shown that, compared with preexercise euhydration, GIH improved peak power output by 5% during an incremental test to exhaustion after 2 hr of cycling during which fluid consumption replaced only 33% of sweat losses (Goulet, Rousseau, Lamboley, Plante, & Dionne, 2008).…”