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by Bonita L. Marks, Ph.D.

Summertime, tennis, and heat all go hand in hand.  One of the most important things you can do to improve your tennis performance is to remember to DRINK!  But do make sure you are drinking appropriate amounts of the RIGHT stuff - products that will be absorbed quickly, give you a fast energy boost and help hydrate you all at the same time.  This automatically rules out beverages with caffeine and alcohol in them as both promote you to lose water (through urination).  In addition, both caffeine and alcohol have other undesirable side effects if taken in larger quantities than what your body can handle (this is body-size dependent- the smaller you are, the less your body can process).  Caffeine will raise your heart rate and blood pressure, something you don't need to have happen as exercise will be doing the same.  The effects of ma juang, ephedra, and ephedrine additives are similar to caffeine-so avoid those too!  Alcohol will increase your lactic acid production which in turn will decrease your ability to tap into your fat stores for energy - thereby inducing fatigue quicker, something you certainly don't want to speed up.

So what are some good hydrating fuels?  Choose ones that will hydrate you as well as maintain your energy and electrolyte balance.  Energy comes from the sugar content - a beverage with 6-8 % carbohydrate (carb) is the easiest to use and has been shown not to cause stomach cramping.  Anything higher than 8% takes longer to digest- the outcome?  The fluid just sits in the stomach longer getting jostled around and may make you nauseous.  Less than 5% really isn't very effective as far as energy boosting goes but the drink may still be effective for sodium loading and general fluid intake.  As for type of carbs, glucose is the easiest to absorb, followed by fructose and sucrose.  In sport drinks, glucose is usually coupled with sucrose and fructose or is listed as the polymer maltodextrin.  Just make sure fructose or corn-syrup is NOT the first ingredient on the ingredient label.  If the drink does have a higher percentage of carbs, and you like it, rather than using it during play, choose the drink to pre-hydrate about an hour before you play or rehydrate with afterwards.  In either case, digestibility won't be an issue.  If you absolutely must use this product while you play (for instance that's the drink your tournament host is giving away for free), dilute the product with water.  In fact, you can do this with any product that feels 'too heavy' for your taste.

Remember the bottom line, your goal is to drink up - even if you don't feel thirsty.  In fact, you should drink about 2.5 cups about 2 hours before practice/match, another 1 cups about 15 minutes immediately before competing/practice, then drink 1-2 cups (4-8 gulps) every 15-20 minutes during your match/practice.  Afterwards, drink 2 cups of fluid for every pound of weight lost (yes, this means keeping track of your weight before and after exercise).  This should be done over the next 3-4 hours when you are recovering, so no need to chug it down.  Space your drinking out while watching others play!  But again, caffeinated and alcoholic products defeat the purpose of rehydrating.  Can you drink too much water?  YES!  This is called hyponatremia - when too much water intake (without electrolytes) dilutes your sodium content.  But this condition is usually not a problem unless you have been exercising in extreme heat for at least 4 continuous hours.

Second, make sure your drink contains sodium (salt), at least 100 mg -this helps your muscles retain water, which will aid in muscle cramp prevention and prevent dehydration.  How much sodium you need depends upon how much you sweat it out.  And that depends upon your genetics, training status, and how long you are exercising in the heat.  If you see white spots where your sweat has evaporated, that is a pretty good indication you need to replenish your sodium - not only in your sport drink but also in your meals.  The only time extra sodium is a problem is if you or your immediate family has a history of high blood pressure and have reason to believe that high salt intake raises your blood pressure.  Otherwise, don't worry too much about your sodium intake if you are competing in hot weather and sweating a lot.  Potassium (another electrolyte; sport drinks need at least 28 mg) and other minerals are also important for muscle function, but these aren't usually lost in the sweat as much as sodium is.  Protein is another popular additive, however sports research has shown that while it may help build up and repair muscle tissue, it is also harder to digest and may cause stomach cramping in some people especially if consumed during exercise.  The only way to know for sure if a sports drink is the right choice for you is to try it out during a routine practice session and see how you feel.

The "top 15" list below is categorized in terms of type of carb load and sodium content.  All are reported to be caffeine-free with no ma-juang or ephedra-like products (which by the way will get you disqualified if your urine is tested for a match).  Of course, whenever carbs and other substances are added, so are calories, from 10 to 100 calories for one cup (8 ounces).  Some of these products are readily available at your grocery stores, others only in health food or sports performance stores (and then they are more expensive as well).  If your drink isn't listed here, just review the ingredients label on your drink's container and make an educated choice.  One last bit of advice - notice that lemonade and other 'healthy' fruit juices aren't listed here---that's because they contain 12-15% fructose plus other heavy sugars, as do sodas.  And your diet sodas do you no good either.  So don't take that stuff out on the court with you!

Top 15 List:
1. Water: 0% carb; pure unless spring water, then it may also contain sodium and some minerals (remember: you can add your own salt packet and flavoring to water!)

2. Pro-Hydrator (InterNutria, Inc.): 0% carb; glycerol (not a carb), 2.5 mg sodium

3. Propel (by Gatorade): 1 % carb; purifed water with vitamins and 35 mg sodium added

4. Pedialyte (Ross Labs): 2.5% carb: glucose-fructose, 248 mg sodium

5. Rehydralyte (Ross Labs) 2.5% carb: glucose, 407 mg sodium

6. Gatorade (Quaker Oats Co.): 5-6% carb: sucrose-glucose-fructose, 110 mg of sodium

7. 10-K (Beverage Products Inc): 6% carb: sucrose-glucose-fructose, 52 mg sodium

8. Cytomax (CytoSport, Inc) 6% carb: high fructose-corn syrup-maltodextrin, 70 mg sodium

9. Sqwincher (Universal Products Inc): 7% carb: glucose-fructose, 60 mg sodium

10. PowerBar Perform (PowerBar Inc): 7% carb: glucose-fructose-maltodextrin, 110 mg sodium

11. CeraSport (Cera Products LLC): 7% carb: maltodextrin, 102 mg sodium

12. Exceed (Ross Labs): 7% carb: glucose polymers-fructose, 50 mg sodium

13. Metabolol Endurance (Champion Nutrition) 7% carb: maltodextrin-fructose; 140 mg sodium

14. Allsport (PepsiCo Inc) 8-9% carb, high fructose-corn syrup, 55-80 mg sodium.

15. Powerade (Coca-Cola) 8-9% carb, high frucotse-corn syrup-maltodextrin, 73 mg sodium

Gatorade Sport Science Institute, PacificHealth Labs, American College of Sports Medicine recommendations, and textbook "Sports & Exercise Nutrition" by McArdle, Katch, & Katch.

Dr. Marks (Bonnie) is an associate professor in exercise physiology at the University of North Carolina in Chapel Hill and conducts research on college and professional tennis players. Her email address is bonnie@bonniemarks.com. If you'd like to know more about her background, you can check out her university website at the following website address: www.unc.edu/depts/exercise/fac_marks.html