Friday, August 22, 2008

Cutting-Edge Research: Hydrating with Glycerol and Carbohydrate Drinks

Dehydration has multiple effects on the body. These range from minor such as diminished physical and technical performance to catastrophic issues like heat stroke. The most effective way to stave off dehydration is to continually consume water (or other beverage) throughout the course of the exercise session. Because soccer is a sport where players usually don’t have a chance to drink during the course of play, hyper-hydration protocols have been used to “saturate” the body before the match. Drinking water for several hours before the start of play is thought to delay dehydration and reduce its severity. Researchers have also shown that adding glycerol to the pre-exercise beverage can enhance fluid retention.

In a study set to be released by the Journal of Strength and Conditioning Research, Dr. Jason Siegler and colleagues studied the effects of carbohydrate beverages with and without added glycerol on hydration, body temperature and performance during a soccer training session. Their work suggests that glycerol-containing beverage might provide better hydration than a drink with carbohydrate alone.

The investigators studied NCAA Division I soccer players. The players completed two, identical 60 minute training sessions. Two hours prior to the start of each session, players drink 500ml (17oz) of a carbohydrate beverage or a carbohydrate beverage containing glycerol (about two tablespoons). The training sessions consisted of 4, 15 minute intervals of technical training and small-sided games. Between the second and third intervals, the players drank an additional 500ml of beverage (the same as they had consumed before training). At the end of each session, they performed and Yo-Yo endurance test to exhaustion. Throughout the sessions, body temperature and heart rate were measures. Before and after sessions, body weight was measured and blood and urine samples were taken.

The environmental temperature during the session was moderate, between 75 and 80° with relatively low humidity. There was little effect of the glycerol-containing beverage on body temperature, blood or urine variables or performance on the Yo-Yo test. However, the loss of body weight after training was slightly less when consuming the glycerol-containing beverage as opposed to the control drink. With the control drink, players lost less that 1% of their body weight but lost 1.5% when drinking the carbohydrate-only drink. Since weight loss during single exercise session is primarily the result of sweat loss, this suggests that drinking a carbohydrate beverage containing a small amount of glycerol might delay the onset of dehydration.

It is important to point out that the ambient temperature in this study was considered moderate and glycerol may be less or more effective in hotter environments. Also, glycerol is probably less effective for shorter, less intense sessions where dehydration is less of a concern.

These results of this study are encouraging. Hyper-hydrating with glycerol in a carbohydrate sports drink slows the loss of fluid without affecting body temperature. Adding glycerol to a sports drink is certainly an easy thing to do. Glycerol can easily be purchased through local health food stores (there it is typically called “glycerin” rather than glycerol). Also, glycerol in small quantities (2 tablespoons as used in this study) is safe and rarely causes any major stomach or intestinal discomfort. Thus, drinking a glycerol supplemented sports drink a few hours before a match may lessen the risk of dehydration and could be beneficial to performance.

Reference:

Seigler JC, Mermier CM, Amorim FT, Lovell RJ, McNaughton, Robergs RA (2008) Hydration, thermoregulation, and Performance Effects of two sports drinks during soccer training sessions. Journal of Strength and Conditioning Research (published ahead of print).