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The Effect of Glycerol Ingestion on Performance During Simulated Multisport Activity

Glycerol-induced hyperhydration has been applied to endurance sport with limited success as a performance enhancement strategy. Hypohydration can impair performance in endurance events such as multisport competitions, therefore hyperhydration strategies that sustain total body water could potentially prevent or attenuate dehydration-mediated decreases in performance. In theory, improved hydration status induced by glycerol prior to exercise will decrease heart rate, rectal temperature, and dehydration and increase sweat rate compared to water hyperhydration, which should confer a competitive advantage and, thus, better performances (Goulet, Robergs, Labrecque, Royer, & Dionne, 2006; Lyons, Riedesel, Meuli, & Chick, 1990; Robergs & Griffen, 1998). Glycerol has been used as a hyperhydrating agent, because it has been shown to be rapidly absorbed and osmotically active; therefore, the fluid intake with glycerol is distributed throughout the body. Glycerol increases blood osmolality when accompanied by large volumes of water (1,500–2,000 ml, or 26 ml/kg body weight) and provides an osmotic drive that augments retention of large quantities of water otherwise eliminated by the kidneys (Wingo et. al., 2004; Robergs & Griffen, 1998). Hyperhydration with glycerol increases fluid retention compared to water alone, thus shown to be performance enhancing in hot conditions in which high fluid losses are likely. However, glycerol-induced hyperhydration studies limited to hot conditions may not be applicable to multisport events held in ambient temperatures. Glycerol hyperhydration was tested on athletes competing in Olympic distance triathlon and showed a significant difference in total time between warm and hot days (Coutts, Reaburn, Mummery, & Holmes, 2002). On the hot day, overall performance times were 5.7% faster in the glycerol group compared with the placebo group, and there was a significant improvement (11%) in the 10-km run performance (p < .05). Montner et al. (1996) investigated pre-exercise glycerol hyperhydration on cycling endurance time and established that the mean exercise time was 21% longer after glycerol ingestion (93.8 ± 13.7 min) than after a placebo solution (77.4 ± 8.7 min; p = .049). Therefore, the current literature suggested that glycerol would be most beneficial when applied to ultraendurance events in hot and humid conditions. Despite the wide range of research on glycerol, the performance benefit at this stage is limited to those competing in long distance events at moderate to high intensity in hot, humid conditions (Inder, Swanney, Donald, Prickett, & Hellemans, 1998; Miller et al., 1983). It is not clear whether these results are applicable to long events held in cool, ambient temperatures. The aim of this study was to determine whether glycerol hyperhydration would improve performance in a long, simulated multisport time-trial (kayak, cycle, and run) under cool, ambient temperatures more so than hyperhydration with water alone. The Effect of Glycerol Ingestion on Performance During Simulated Multisport Activity