A meta-analysis of the effects of glycerol-induced hyperhydration on fluid retention and endurance performance

The authors determined, through a meta-analytic approach, whether glycerol-induced 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.