From Ergo Log
Under normal conditions tennis players benefit little from fast carbohydrates in the form of sports drinks, even during long matches. Sports scientists at the University of Sao Paulo in Brazil draw this sobering conclusion in a study that involved getting experienced tennis players to play against each other for periods of three hours. Supplementation with the rapidly absorbed carbohydrate maltodextrin had hardly any effect at all.
The 12 players that the Brazilians used as test subjects were all 18 years old. They had to play against each other for two sessions of three hours. After each hour the players drank a whole bottle of a sports drink given to them by the researchers.
On one occasion the drink only contained flavours and aromas [PLA]; on the other occasion it contained maltodextrin [CHO]. Maltodextrin consists of chains of 3-20 glucose units, which break up rapidly in the body into separate glucose molecules. The players consumed 0.5 g maltodextrin per kg bodyweight per hour. So if you weigh 80 kg you’d get 40 g maltodextrin per hour.
The researchers asked their subjects how tired they were feeling after each hour of play. They had expected the players to feel less tired after being given maltodextrin, but the results weren't convincing. The players in the maltodextrin group did report a miniscule amount less fatigue at the end of the three hours than the players in the placebo group, but the difference was not statistically significant.
The researchers measured the concentration of cortisol, testosterone and immunoglobulin A [an indicator of resistance to viruses] in the subjects' saliva. The only one that reacted to maltodextrin supplementation was the cortisol level. The figure above shows that the cortisol concentration rose less when the players had been given maltodextrin.
So if you just play tennis once a week, you can manage fine without carbohydrate-rich drinks. But the researchers think that players who participate in tournaments lasting several days, playing matches that last up to five hours, may benefit from carbohydrate supplementation.
"These match demands may compromise glycogen stores, which have been associated with decreased physical performance and early fatigue", the Brazilians write.
"Because carbohydrate ingestion helped to maintain glycemia and blunted cortisol response over a prolonged tennis match play in elite junior players compared to placebo, this dietary strategy may be beneficial during tournaments when several matches are played in short period of time."
J Strength Cond Res. 2013 Jul 15. [Epub ahead of print].