Exercise and Dehydration

Q. I exercise a lot and sweat more since the weather is getting warmer. Are sports drinks the best liquids to keep my body hydrated?

A. Whether you're doing high-intensity workouts or just work up a sweat walking your dog around the block, proper hydration is important. Without the proper intake of fluids, you may experience dehydration. Before deciding which fluids are right for you, let's consider the intensity levels of your activities.

Replenishing for low-intensity exercise

In general, water is usually all that is needed to replace fluid loss from sweat due to recreational exercise of less than one hour in duration. If you've been drinking sports drinks after short, low-intensity exercise sessions, you may be spending money on a product your body doesn't need, as well as refueling with calories you just worked hard to burn off. So for many people, water may be the best liquid.

Fuel for high-intensity workouts

If your activity is at a high-intensity level and lasts longer than 60 minutes, a simple sports drink containing 6 to 8 percent carbohydrates—60 to 80 calories per cup—can help rehydrate your body and maintain exercise performance. Sports drinks are designed for individuals who push their bodies to extreme limits during athletic activities. They contain a mixture of water, carbohydrates such as glucose, sucrose, and maltodextrin and electrolytes, including sodium, potassium, etc. Some even add a little protein to the mix. But no matter what the formula, the goal is to provide enough water and energy for the muscles to maintain optimum performance while exercising, as well as to help the muscles and liver recover after their intense activity by replacing glycogen, the storage form of glucose.

Another option is to drink water along with a small energy-boosting snack, such as an apple with peanut butter or honey, a sports nutrition bar, or energy gel. And, for those extreme workouts lasting more than three hours—triathlons, long distance biking or running—sports drinks containing carbohydrates plus electrolytes may be beneficial.

Causes of dehydration

As you consider how to rehydrate your body, it's important to be aware of factors that contribute to dehydration. They include the following:

• Your rate of perspiration (some people perspire at a quicker pace than others, resulting in a quicker drawdown of their fluid volume, which in turn, increases their risk for dehydration)
• The intensity of the workout (slow and steady or fast and furious; whether short bursts of speed or power are incorporated, etc.)
• The environmental conditions—whether it's hot and humid, cold and dry, windy, etc.
• The time frame of your activity; the longer the exercise, the greater the fluid loss from sweating and breathing
• Your altitude—more fluid loss occurs with higher-altitude exercising
• Your current state of hydration; you may be underhydrated even before your activity
• Your present state of health (if you have diarrhea, frequent urination due to diabetes, other health conditions, etc.)

When athletes sweat and lose two percent or more of their body weight, a significant deterioration in performance may occur. At higher levels of dehydration, the blood volume drops and the heart rate increases. This may lead to dizziness, fatigue and muscle cramps.

Anticipate your fluid loss

One way to ward off dehydration is to anticipate your fluid loss for certain activities. Weigh yourself before and after your regular activity and examine the percent change in your weight. For example, if you usually run 10 miles per day and weigh 150 pounds before exercise and 147 pounds after, your 2 percent weight loss was most likely a temporary change due to fluid loss from perspiration, and possibly urination. To correct that water deficit, it may be necessary to consume a little more than a liter of fluid.

While your individual approach to proper sports hydration should be discussed with your physician or a registered dietician certified in sports dietetics, consider the following guidelines:

• Before exercise: Drink 15 to 20 ounces of water or sports drink two hours prior to the start, as well as 8 to 10 ounces 15 minutes before exercise.
• During exercise: Drink 7 to 10 ounces of water or sports drink every 15 minutes while engaged in the activity.
• Within two hours after exercise: Speak with your physician as calculations are based on a formula including water weight lost.

Water intoxication

Lastly, our bodies are a system in balance. While correcting a fluid deficit is important, over-correcting with too much water has the potential to lead to water intoxication, or hyponatremia (low sodium in the blood). While this is a rare occurrence, it is a real possibility with early warning symptoms—nausea, muscle cramps, slurred speech, confusion—that may be mistaken for dehydration. In extreme cases, it can be fatal.

Those at greater risk are participants in high intensity and long duration events (triathlons, marathons, etc.), as these activities tend to lead to extra sodium loss due to excessive sweating. Sodium replacements with a sport drink or other home remedy (pickles, chicken soup, etc.) is often preferred to water alone during these extreme body challenges.

For more information on hydration and exercise, take a look at the American College of Sports Medicine and the American Dietetic Association.

Read More from Dr. Rob on MSN Health & Fitness:

• Stop Fueling Your Fatigue
• Allergic to Water?
• A Buyer Beware: Natural Energy Supplements Can Pose Risks
• Running on E

Find all articles by Dr. Rob.

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Robert Danoff, D.O., M.S., is a family physician and program director of The Family Practice Residency, as well as the combined Family Practice/Emergency Medicine Residency programs at Frankford Hospitals, Jefferson Health System, Philadelphia, Pa. He is the medical correspondent for CN8, The Comcast Network, a regular contributor to Discovery Health Online and a contributing writer to The New York Times Special Features. (Read his full bio.)