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Ask the High Performance Lab -- August 23

May 25, 2008 12:25 PM

PLEASE NOTE: The medical opinions in USTA.com's Ask the High Performance Lab are responses intended for the average player. Please consult with your primary physician before beginning any new exercise program.

Q: Competing in temperatures over 100 degrees, I have suffered heat exhaustion twice. I seem to also be more prone to dehydration and I'm a bit nervous to compete in the heat since then. Is there anything I can do 3-4 days prior to competition other than major hydration?

Michael F. Bergeron, Ph.D., FACSM is an applied physiologist and Assistant Professor at the Medical College of Georgia in Augusta, GA in addition to serving on the USTA Sport Science Committee.© USTA
The primary factors contributing to heating your body up during play are the environment (temperature, humidity, and solar radiation) and intensity of play. Importantly, an excessively elevated body temperature and inability to compete can occur, even if you begin your match well hydrated and attempt to drink sufficiently during play.

Of course, if you develop a significant fluid deficit through sweating, this can also have an additional profound negative effect on your capacity and desire to continue. So hydration is indeed important, and you should be drinking plenty of appropriate fluids (e.g., water, juice, milk, sport drinks) throughout the days leading up to a tournament, especially if it’s going to be hot.

Adequate hydration also requires sufficient intake of other nutrients such as carbohydrates and certain electrolytes before play. Other controllable and contributing variables include your fitness, choice of clothing on court, rest and sleep, and tapering training before a competitive event begins.

All of these factors will affect your tolerance of play in the heat. If you continue to have problems, you may want to consult with a physician or sports physiologist who could directly assess your on-court responses related to exertional heat strain.

Q: Why are pro players provided with bananas during their matches? Would the potassium from the bananas not take a long time to be absorbed into their systems? Plus, bananas are 'heavy' in the stomach. Are there not any better sources of potassium and high energy foods that are more easily absorbed?

A more appropriate question would be “Should players consume bananas during matches?” Bananas are convenient and a great source of several important nutrients. However, bananas are not a great choice for high or rapid energy during play. In fact, a banana is a much slower provider of utilizable energy compared to a number of other carbohydrate sources, such as some sport drinks and foods (e.g., sugar-based candies, glucose gels, or even white bread) that would raise the blood sugar quickly.

Moreover, potassium replenishment during play is not a priority. To maintain performance and avert muscle cramps due to sweating, water, carbohydrate, and sodium chloride (salt) are the nutrients that a player needs to focus on consuming on court.

Q: Is it possible to drink too much liquid during a match? Last Monday night I drank over 66 ounces of water and 10 ounces of Gatorade and I was still thirsty. During the day, I drank way over my limit too (over 100 ounces)! I am a 130 pound woman in good physical shape, but I seem to drink more than everyone else and wonder why.

Yes; it is possible to drink to much fluid during play and off the court. However, without knowing your sweat rate during that match, your hydration status before your began play (You may have started the match significantly dehydrated.), and the length of the match, it’s difficult to assess whether or not the fluid consumption that you described was appropriate.

Some adults can tolerate (and should consume, based on their sweat rate) up to 2 liters (about 70 ounces) of fluid per hour during play. Again, if you sweat a lot and the match lasts 2 hours, then 76 ounces of total fluid consumption might not even be enough! If you feel the need to drink that much, you likely need it.

Now, on the other hand, if you are over-consuming fluid (particularly low- or no-sodium fluid) over a relatively short period of time (on the court or off), at the least, you’ll likely have to go to the bathroom more than usual. More seriously, you could induce a certain level of hyponatremia (low blood sodium) that could lead to problems ranging from poor performance to seizures or even worse. Notably, some women may be more at risk for fluid overload and hyponatremia due to their size and, at times, contributing effects of estrogen.

Michael F. Bergeron, Ph.D., FACSM is an applied physiologist and Assistant Professor at the Medical College of Georgia in Augusta, GA in addition to serving on the USTA Sport Science Committee. His research includes studies on exercise and sports performance and nutrition, with an emphasis on the effects of exercise in the heat on fluid and mineral balance, as well as thermal and cardiovascular strain. Dr. Bergeron has worked with a number of junior, collegiate, and professional tennis players on training and nutrition related to preparation, competition, and recovery in the heat.

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