The effect of glycerol hyperhydration on olympic distance triathlon performance in high ambient temperatures.
ABSTRACT The purpose of this study was to examine the effect of prior glycerol loading on competitive Olympic distance triathlon performance (ODT) in high ambient temperatures. Ten (3 female and 7 male) well-trained triathletes (VO2max = 58.4 +/- 2.4ml kg(-1) min(-1); bestODTtime = 131.5 +/- 2.6 min) completed 2 ODTs (1.5-km swim, 40-km bicycle, 10-km run) in a randomly assigned (placebo/ glycerol) double-blind study conducted 2 weeks apart. The wet-bulb globe temperature (outdoors) was 30.5 +/- 0.5 degrees C (relative humidity: 46.3 +/- 1.1%; hot) and 25.4 +/- 0.2 degrees C (relative humidity: 51.7 +/- 2.4%; warm) for day 1 and day 2, respectively. The glycerol solution consisted of 1.2 g of glycerol per kilogram of body mass (BM) and 25 ml of a 0.75 g x kg(-1) BM carbohydrate solution (Gatorade) and was consumed over a 60-min period, 2 hours prior to each ODT. Measures of performance (ODT time), fluid retention, urine output, blood plasma volume changes, and sweat loss were obtained prior to and during the ODT in both the glycerol and placebo conditions. Following glycerol loading, the increase in ODT completion time between the hot and warm conditions was significantly less than the placebo group (placebo 11:40 min vs. glycerol 1:47 min; p < .05). The majority of the performance improvement occurred during the final 10-km run leg of ODT on the hot day. Hyperhydration occurred as a consequence of a reduced diuresis (p < .05) and a subsequent increase in fluid retention (p < .05). No significant differences were observed in sweat loss between the glycerol and placebo conditions. Plasma volume expansion during the loading period was significantly greater (p < .05) on the hot day when glycerol appeared to attenuate the performance decrement in the heat. The present results suggest that glycerol hyperhydration prior to ODT in high ambient temperatures may provide some protection against the negative performance effects of competing in the heat.
Article: PRE-EXERCISE HYPERHYDRATION: COMMENTS ON THE 2007 ACSM POSITION STAND ON EXERCISE AND FLUID REPLACEMENT[show abstract] [hide abstract]
ABSTRACT: Goulet EDB. Pre-Exercise Hyperhydration: Comments on the 2007 ACSM Position Stand on Exercise and Fluid Replacement. JEPonline 2008;11(2):64-74. In the latest hydration guidelines of the ACSM (February 2007), two paragraphs are dedicated to the effects of pre-exercise hyperhydration (PEH) on exercise endurance performance (EEP) and physiological functions. With respect to its ergogenic potential, the Position Stand of the ACSM concluded that PEH only occasionally improves EEP, or offers no clear performance advantage. These conclusions are, in my opinion, not a perfect reflection of what is really known about the ergogenic value of PEH, as they were derived from results of studies whose experimental designs are inadequate to determine the ergogenic property of PEH. In this opinion/review article, I will provide an alternative view of the effect of PEH on EEP using newly published, as well as results not discussed by the ACSM Position Stand. When the literature is carefully reviewed, one finds out that only few investigations provide clues about the effect of PEH on EEP, and collectively their results suggest a performance-enhancing effect in athletes. On the other hand, the Position Stand judged that this strategy provides no thermoregulatory or other clear physiological advantages, and that it increases the risk of hyponatremia and of having to void during competition. I am not in total agreement with these conclusions and here I will present evidence suggesting otherwise. I believe that it is important to provide an alternative view of the effects of PEH on EEP and physiological functions than that given by the ACSM's Position Stand due to the influential role of this organization within the exercise science community.