Anyone who regularly watches competitive singles tennis, football or soccer has probably seen an athlete in the throes of pain brought on by muscle cramping. There are probably as many reasons for muscle cramps as there are nutrition suggestions to cure them. But in sports, especially in long-duration events played in hot environments, the most likely cause of cramps is loss of sodium through sweating.

Many athletes have heard the public health message that sodium is bad and a high-salt diet will lead to high blood pressure and heart disease. Add to that the fact that many athletes have parents with high blood pressure, so they often cut back on their sodium intake. However, athletes who sweat heavily and especially those who are "salty sweaters" need to deliberately replace through diet the salt lost in sweat.

CHRIS ROSENBLOOM FIT TO EAT Have a question of general interest? E-mail Rosenbloom Related: • More on food and drink • Restaurant reviews and search More Rosenbloom You can work '101 Foods' into your diet  Know your nutrition: A quick quiz for fall  Three to be careful with in healthy diet  Grapefruit, cancer link considered preliminary  Beta carotene powers orange fruits, veggies  Our levels of the 'sunshine' vitamin decrease as we age  'Repair' muscles after long-distance running  Food-drug interaction an important issue  • Chris Rosenbloom, Ph.D., R.D., is a member of the nutrition faculty in the College of Health and Human Sciences at Georgia State University.

How do you know if you are a "salty sweater"? When you sweat, does it sting your eyes and leave a salt layer on your skin when it dries? When they dry, do your shorts, T-shirt or cap have visible salt lines? These are indications that you are a "salty sweater."

Mike Bergeron, associate professor and exercise physiologist at the Medical College of Georgia, studies the effects of exercise in the heat. His research with competitive tennis players, from juniors to professionals, has led him to develop practical guidelines for athletes who experience muscle cramping.

"Exercise-associated muscle cramps are sometimes referred to as heat cramps, but athletes can develop such cramps in cool exercise conditions and even indoors," says Bergeron. "The athletes that I work with who cramp have one thing in common — a sweat-induced sodium deficit; that is, they lose significant amounts of sodium in their sweat during training and competition."

Bergeron measures sweat loss and calculates sodium loss in tennis players and other athletes and reports that sweating can easily be as great as 2.5 liters (about 88 ounces) or more with 2,500-5,000 milligrams of sodium lost per hour of exercise.

Consider that competitive tennis matches can last several hours; that's a lot of fluid and sodium to replace. To put it in perspective, the average American consumes 8 to 12 grams of salt or 3,150 to 4,700 milligrams of sodium in a day. People with high blood pressure are encouraged to consume no more than 6 grams of salt or about 2,400 milligrams of sodium per day. So it is easy to see that some athletes are unnecessarily and inappropriately restricting salt in their diet when they are training and competing.

Bergeron recommends that, at the first sign of muscle twitches (an indication that full-blown cramps may be imminent), athletes take an "emergency" drink consisting of a half-teaspoon of salt added to a half liter (16-20 ounces) of a carbohydrate-electrolyte drink, like Gatorade, shaken well, and consumed all at once or over 5 to 10 minutes.

This can be followed by a little water to get rid of the salty taste and to help get the sodium into the body faster. This has been a proven strategy for preventing muscle cramps, and athletes can often promptly continue exercise without cramping for an hour or more, while drinking additional lower-sodium-concentrated fluids at regular intervals.

Off the court or field of play, athletes who lose a lot of sodium should replace the rest of it via their diets. The easiest way to do that is with liberal use of the salt shaker with meals and eating or drinking salty foods like chicken, beef, vegetable broths, tomato juice and pretzels. While other electrolytes, like potassium and calcium, are also found in sweat, "They are lost to a much lesser extent than sodium and are falsely implicated in causing muscle cramps," Bergeron adds. So, put down the bananas and reach for the salt if you experience exercise-related muscle cramps.

Where to get some sodium
• 1 cup (8 ounces) of a sports drink ranges from 53 to 110 milligrams sodium
• 1 cup (8 ounces) of an endurance-formula sports drink equals 200 milligrams sodium
• 1 dill pickle spear equals 385 milligrams sodium
• 1 French bread pizza (frozen) equals 600 milligrams sodium
• 5-ounce chicken burrito equals 740 milligrams sodium
• 1 cup chicken broth equals 760 milligrams sodium
• 1 cup (8 ounces) tomato juice equals 877 milligrams sodium
• 1 tablespoon soy sauce equals 1,000 milligrams sodium
• 10 pretzel twists equal 1,000 milligrams sodium
• 1 cup canned beef stew equals 1,120 milligrams sodium