Chemistry Reference
In-Depth Information
As was mentioned earlier, the carbohydrates in sports drinks should provide an alternative to
liver and muscle glycogen energy source for oxidation, which will result in improved maintenance
of blood glucose. Several attempts of mixing glucose and sucrose, glucose and fructose, or a combi-
nation of maltodextrin and fructose in beverages that increase exogenous carbohydrate oxidation to
a level greater than 1.2 g min
-1
have been made (Jentjens et al. 2004, 2005; Jentjens and Jeukendrup
2005; Wallis et al. 2005). However, fructose ingestion on its own is not recommended, because it is
not so effective in improving performance and may also cause gastrointestinal problems (Murray et
al. 1989; Bjorkman et al. 1984).
Despite the fact that the majority of studies have reported positive results in exercise perfor-
mance as a result of ingesting carbohydrate-electrolyte drinks during exercise, the exact mecha-
nism by which this is achieved is not clear. A better maintenance of blood glucose and carbohydrate
oxidation late in exercise (Coggan and Coyle 1987; Coyle et al. 1986) with a reduced liver glucose
output (McConell et al. 1994) has been observed during cycling; whereas in running, a reduced
muscle glycogen use in type I ibers has been reported (Tsintzas et al. 1995). Another mecha-
nism, although without possessing such strong evidence as the previous ones, might be the reduced
plasma-free tryptophan to branched chain amino acid ratio when carbohydrates are ingested. This
leads to a reduction in the synthesis of the neurotransmitter serotonin (5-hydroxytryptamine) in the
brain. Serotonin has the potential of reducing mental and physical performance during prolonged
exercise (Davis et al. 2000). Recently, a number of studies have shown that sports drinks may pro-
vide a beneit to the athlete by simply mouth-rinsing these solutions and not ingesting them during
short (1-h) endurance exercise. Researchers explain this amazing inding by data that show that car-
bohydrates in the mouth stimulate reward centers in the brain, lower the perception of effort during
exercise, and increase corticomotor excitability (Rollo and Williams 2011).
11.6.3 Ingestion of Carbohydrates during recovery
After the completion of exercise, body luids and glycogen stores must be restored. This should
be done as soon as possible if a subsequent exercise bout is to take place. In terms of restoring
euhydration, athletes need to drink about 1.5 L of luid for each kilogram of body weight lost.
Consuming sports drinks and snacks with sodium will also help recovery by stimulating thirst
and luid retention (American College of Sports Medicine 2007). As far as glycogen resynthesis is
concerned, the consumption of 1.0-1.5 g of carbohydrate per kilogram of body mass within 30 min
after exercise and at 2-h intervals up to 6 h is recommended (American College of Sports Medicine
2009). Furthermore, carbohydrates with a high GI may result in higher muscle glycogen levels com-
pared with the same amount of carbohydrates with a low GI (Burke et al. 1993).
In conclusion, sports drinks containing carbohydrates and electrolytes may be consumed before,
during, and after exercise to help maintain blood glucose concentration, provide fuel for muscles,
improve performance, and decrease the risk of dehydration.
reFereNCeS
Abdallah, L., M. Chabert, and J. Louis-Sylvestre. 1997. Cephalic phase responses to sweet taste.
Am. J. Clin.
Nutr.
65: 737-743.
Agus, M. S. D., J. F. Swain, C. L. Larson, E. A. Eckert, and D. S. Ludwig. 2000. Dietary composition and
physiological adaptations to energy restriction.
Am. J. Clin. Nutr.
71: 901-907.
Ahlborg, B., J. Bergstrom, L.G. Ekelund, and E. Hultman. 1967. Muscle glycogen and muscle electrolytes dur-
ing prolonged physical activity.
Acta Physiol. Scand.
70: 129-142.
Al-Waili, N. S. 2003. Effects of daily consumption of honey solution on hematological indices and normal
levels of minerals and enzymes in normal individuals.
J. Med. Food
6 (2): 135-140.
Search WWH ::
Custom Search