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Body Temperature, Dehydration, and Performance

April 3, 2003 04:43 PM

by Jim Brown, Ph.D.

In the period of a few hours, tennis players get hot, become dehydrated, take a rest, then go out to compete or train again. They think they have rehydrated during their rest periods, but there is an increasing body of evidence to the contrary.

Listen to Dr. Michael Bergeron, Assistant Professor of Pediatrics at the Medical College of Georgia.

"Tennis has a history of heat problems during summer tournaments among junior players and the problem seems to be getting worse. "Kids are playing two or three matches a day in extreme conditions, so it is not surprising that as many as six to eight players are being taken to the hospital every day."

Bergeron and a colleague designed a study to answer these questions:

1) How bad is the playing environment?

2) How are players responding to high heat and humidity?

3) Are the athletes who are not getting enough fluids primarily the ones who are overheating or are well-hydrated players experiencing the same problems?

4) Is this a management problem or the inability of young athletes to handle adverse conditions?

Tournament Conditions

"The competition site we selected was a national tournament for boys 14 and under in San Antonio, Texas, during August. That's probably the most stressful environment you can find. It's just an awful time and place to play."

Bergeron determined pre-match hydration of the players through urine concentration tests. The players' core body temperatures were taken with an ingestible temperature sensor. Temperature levels were measured several times during each match.

The average end-of-first-match core temperature was 101.6. In one player it was 104.1 Ten minutes later, the average temperature had not significantly decreased.

"Hydration status before play was correlated with body temperature during competition," explains Bergeron. "As the match went on, the correlation became even stronger. If a player enters a match dehydrated, it's in his interest to get off the court quickly. The longer play continues, the greater the dehydration will have on elevating core temperature."

"We also took into consideration that players typically participate in a singles match in the morning and then play again in the afternoon. Overall, they did a poor job of rehydrating. They tended to come back after a break of almost four hours significantly more dehydrated than they were when they began their morning matches."

Practice Conditions

Bergeron then shifted his attention to a group of players 13-20 years old in Florida. Under very warm and humid conditions, he examined hydration status and core body temperature. This time the measurements were taken before, during, and after an intense, two-hour practice session.

The Florida group recorded lower body temperatures when they began practice dehydrated. Why? Bergeron speculates that, in practice, players self-regulate (slow down) rather than maintaining a high intensity level. In competition, they are more inclined to they push themselves, possibly to a danger point.

The Lesson

"What you can get away with in practice, you can't get away with in competition," thinks Bergeron.

"The penalties are a faster onset of fatigue, diminished endurance, and compromised muscle strength. Basically, it results in lower performance. The athlete will have a poorer capacity for temperature regulation and be at greater risk for heat illness."

One other finding of Bergeron's research: the younger the player, the higher the core body temperature.

Questions About Guidelines

Bergeron questions current recommendations for rehydration. "Many athletes incur extraordinary fluid losses. Some professional tennis players lose as much as 3.5 liters per hour during intense singles play. Following guidelines to drink a cup of fluid every 15-20 minutes would really make them come up short."

"Even older adolescents could lose ten liters of fluid during a match that lasts 3-4 hours. If he consumes six liters during the match, he would still finish the match down four liters and may have to play again the same day. Post-play hydration efforts have to be taken seriously. Remember that consuming too much no- or low-sodium fluid can lower the blood sodium to dangerous levels."

Urination Not Reliable Indicator

"Just because you are urinating regularly doesn't mean you are fully hydrated. Diluting the blood by consuming fluids with little or no sodium readily causes a response that triggers urination. Unless you put salt back into the body at the same time, there is less of a tendency to hold and distribute fluids throughout the body. Athletes need to take in electrolytes such as sodium and chloride, as well as carbohydrates, if they want to fully hydrate. If they don't, rehydration will remain incomplete."

Jim Brown will be contributing new content to this site on a monthly basis. If you have a question for Dr. Brown please feel free to email him at sportsmed@mindspring.com.




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