Glycerol is a chemical compound which forms the backbone of the triglyceride molecule (glycerol plus 3 fatty acids), the molecular form of lipids stored in the fat cells. A clear, syrupy, and extremely sweet substance, glycerol has water retaining effects when taken orally.

Robergs RA et al in their review "Glycerol. Biochemistry, pharmacokinetics and clinical and practical applications." Sports Med 1998 Sep;26(3):145-67, noted that glycerol infusion and ingestion have been used in research settings for almost 60 years, with widespread clinical use between 1961 and 1980 in the treatment of cerebral edema resulting from acute ischemic stroke, intraocular hypertension (glaucoma), intracranial hypertension, postural syncope and improved rehydration during acute gastrointestinal disease.

In 1987, it was shown that resting subjects drinking a glycerol solution retained 50% more fluid than when drinking a similar volume of water alone. This led to investigation of its ability to help prevent dehydration under extreme conditions of exercise, heat, and high humidity.

A follow-up study in 1990 demonstrated that subjects pre-loaded with a glycerol solution did sweat at a greater rate with exercise (but remember they started out with an overall excess of total body water from the water retention effects). Overall they demonstrated a net positive effect on fluid balance (less plasma volume depletion) while maintaining a lower core body temperature (presumably a combination of more efficient circulation from the increased plasma volume and the higher rate of heat dissipation with perspiration).

In 1992, 11 cyclist rode to exhaustion at 60% VO2 max. The group pre-hydrated with a glycerol/water mix compared to water alone improved their endurance by 22% (94 vs. 77 minutes). A repeat study using the same prehydration approach, but adding a replacement program (while riding) of water alone (for the pure water prehydration group) vs. a sports drink (for the glycerol prehydrated group) revealed an even greater advantage of 32% (93 minutes for water alone vs. 123 minutes with the glycerol and sports drink regimen). And this has been upheld with a third study which prehydrated one group with glycerol (1.2 grams glycerol/kg body wt. in a total volume of 5 ml/kg body weight) 1 hour before a ride at 60% VO2max. Both groups (glycerol pretreated, pure water) drank 9 ml/kg/hr of a 5% dextrose solution during the ride. The glycerol pretreated group increased their time to exhaustion by 24%.

Possible side effects include headache and nausea which could hinder OVERALL performance results for any single individual. However, they appear to be unusual if proper concentrations are used (one researcher who has used glycerol on 200 subjects reports only 2 or 3 did not tolerate it). It should be considered a potential performance enhancer for any ride lasting an hour or more, particularly under the adverse conditions of high heat and humidity.

However, several recent papers presented at the American College of Sports Medicine (1997) failed to show any difference between pre ride hyperhydration with glycerol or with water alone in time to exhaustion and Wagner DR in his review "Hyperhydrating with glycerol: implications for athletic performance" in Am Diet Assoc. 1999 Feb;99(2):207-12 noted that while "small decreases in hydration status can result in a dramatic decrement in athletic performance and greatly increase the risk of thermal injury .... the results of glycerol-induced hyperhydration research have been equivocal, most likely because of methodological differences between studies, such as variations in the intensity of exercise, environmental conditions, and concentration or dose of glycerol administered." And to top it off, glycerol has recently been banned by the UCI (international cycling's governing body).

As far as commercial suppliers, one can order "Glycerate" from Advanced Kinetics 800-295-4335 or go to Internutria, a website offering a commercial drink containing glycerol.

If you decide to give it a try, experiment in training, not on a ride. Prepare a solution of 1 gram of glycerol per kg of body weight (1 pound = 0.454 kg) and mix it with or follow with 20 - 25 ml of water per kg of body weight (about 1.5 liters). Mixing it with a small amount of orange juice to taste and following with the water "chaser" is one approach. You may feel a little bloated for 20 to 30 minutes, but continue to eat carbos and drink water or a sports drink at your regular rate while riding.

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