What to drink on your summer run or bike ride — sports drink or water? The answer is not always as clear as, say, water. It depends on the duration and intensity of the physical activity and on how much you sweat, says Suzanne Girard Eberle, sports dietitian and author of “Endurance Sports Nutrition.”

“The basic guideline for most people is that if you are doing continuous exercise for 60 minutes or less, then water is fine,” Girard Eberle says. “But beyond 60 minutes and if the intensity is high, you should consider a sports drink.”

This is because sports drinks include electrolytes (which help regulate nerves and muscles), carbohydrates (which help restore the body’s glycogen — or fuel — levels) and water (which helps hydrate).

“Sports drinks really do triple duty whenever you exercise for longer periods of time,” Girard Eberle says.

They not only help the body achieve optimal performance during exercise, like giving the body that extra carbohydrate kick when fuel levels have been tapped, but can be crucial for properly maintaining an endurance athlete’s body functions.

But electrolytes (which include sodium, potassium, calcium and magnesium) are not created equal.

Pass the salt

“Sodium is by far the most important while exercising,” says Cedric Bryant, a physiologist and chief science officer at the American Council on Exercise, a nonprofit group dedicated to fitness education and certification. Sodium is found in salt.

Mary Perry, a sports nutritionist and owner of Dynamic Nutrition in Alexandria, agrees and adds: “Sometimes I even tell people to salt their food more to get the sodium they need for exercise.”

But sodium, you might say, aren’t we supposed to cut that rather than add it?

“That public health message goes out to the average American who struggles to get the recommended 30 minutes of exercise a day,” Girard Eberle says. “If you are exercising for long durations and at a high level of intensity, you need sodium.”

According to the USDA’s Dietary Guidelines for Americans 2010, the average person should consume no more than 2,300 milligrams of sodium per day. The average consumption is over 3,000 mg. Much of the sodium comes from processed foods, which fitness enthusiasts often skip.

“Women are particularly vulnerable to sodium depletion since we take public health messages to heart — maybe a little too much,” Girard Eberle says.

In order to get this extra sodium, you could in theory — aside from sports drinks — just add a pinch of salt to your water bottle. But the taste might discourage you from drinking altogether and that would obviously defeat the purpose.

“I recommend that people consume the beverage — excluding alcohol and soda, of course — that will encourage them to maintain a good hydration level particularly when working out in the heat,” Bryant says. “This recommendation is true for kids, too.”

Don’t worry about the carbohydrates or calories of a sports drink if you exceed the 60 minutes in a workout, Perry says.

“These sports drinks are engineered to have the perfect levels of carbs and electrolytes, and they are relatively low in terms of calories,” Perry says.

Take Gatorade G2, for example. It contains 20 calories per serving (eight ounces), 110 mg sodium, 30 mg of potassium and 5 grams of carbohydrates.

And how about the ubiquitous coconut water?

“It’s kind of a natural sports drink. The problem is it doesn’t contain much sodium,” Perry says.

In a serving (eight ounces) of one brand of popular coconut water, there are 43 calories, 39 mg of sodium, 495 mg of potassium and 11 grams of carbohydrates.

Potassium is important for the body but isn’t as crucial to replace during exercise as sodium, Perry says.

How much to drink?

All three experts recommend the “pee test.” In other words, every time you urinate check the color. It should be the color of light lemonade. If it’s darker, you are dehydrated. If it’s lighter, you are over-hydrated, another danger that can lead to everything from headache to coma, even death in severe cases.

A good guideline for the amount of fluid needed even before exercising is to take your weight and divide it by two. That quotient represents the number of fluid ounces you should consume in a day.

In other words, if you weigh 100 pounds, you should take in 50 ounces (just over 6 cups) per day, remembering that food, too – particularly juicy vegetables and fruits like watermelon and cucumber – contains lots of fluid.

And if you plan to exercise, up the intake by 2 to 3 cups (16-24 ounces) before exercising and another cup every 15 minutes while exercising, Bryant says. Cold drinks are preferable as they are more easily absorbed in the stomach, he says. Add a cup or two after exercising.

Another way to identify hydration needs is to measure the sweat rate. Weigh yourself before exercise and after to see how much fluid you have lost to sweat. For every pound you have lost you should replenish with 21 / 2 cups of fluid.

“If you are losing up to 3 percent of your body weight, then you are not doing enough during exercise to hydrate,” Girard Eberle says, adding that we should not only ask what the body can do for us but also what we can do for the body.

“If you respect your body and it’s doing all this work for you, shouldn’t you ask what you owe it?”

Boston is a fitness trainer and freelance writer.

Read past columns by Vicky Hallett and Lenny Bernstein at washingtonpost.com/wellness . There, you can subscribe to the Lean & Fit newsletter to get health news e-mailed to you every Tuesday.

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