Maintaining proper hydration can be a challenge in the summer heat, especially for active-duty service members who are exercising and following training regimens. Doctors from the Military Health System say water, nutrition and preparation are necessary to avoid dehydration.

You should drink water after being in the heat or exercising, but if you’ve been doing physical exertion for more than an hour, you also need electrolytes and calories, said Dr. Jeff Leggit, associate professor of family sports medicine at the Uniformed Services University of Health Sciences (USU) in Bethesda, Maryland.

If the body is not properly hydrated for a long period of time, its balance of electrolytes, sodium and potassium is thrown off. This can cause metabolic changes that affect everything from the brain to muscles and joints to blood flow. Dehydration can cause muscle soreness, muscle breakdown, fatigue, lightheadedness, dizziness, even kidney problems. It can also affect your thinking.

“You don’t think as well if you’re hungry or thirsty,” said Leggit. In the military, that’s particularly important. “Individual degradation performance, unit degradation performance and mission degradation performance are all possible consequences, in addition to the medical problems.”

Air Force Lt. Col. (Dr.) Christopher Jonas, USU assistant professor of family and sports medicine says to be prepared and have fluids close by when you are exercising.

“It is important to stay ahead of thirst by hydrating before, during and after exertion,” said Jonas. “Watch your energy level, how much you sweat, the heat and humidity, and how much exertion you will be doing.”

A rule of thumb for water intake has always been eight glasses of water a day, but it is different for each person. Watch for signs that you might not be getting enough water: monitor the color and concentration of your urine and how much you’re sweating—not just the day you exercise, but the days prior as well. Darker yellow or cloudy urine means your body needs water.

Service members are also at risk for rhabdomyolysis, or muscle breakdown, when highly dehydrated, overworked or both while in hot weather. The body breaks down muscle to some degree during physical activity, potentially causing soreness. The rebuilding of muscle is what provides increased strength. However, exercising while dehydrated and in a hot environment can cause muscle cramps or rhabdomyolysis, which occurs when people do more than their bodies can handle.

“Listen to your body,” said Leggit, who advises avoiding increasing an activity or intensity by more than 10 percent per week. “If you’re in pain the next day, you did way too much. There’s a difference between pain and being sore.”

Extreme cases of muscle breakdown can require aggressive fluid rejuvenation through IVs. In addition to staying hydrated, exercising earlier or later in the day, moving activities indoors, being mindful of ingredients in supplements and having a good nutrition strategy can help prevent muscle injury due to summer heat.

“We recommend physical activity, and neither the heat nor the cold should preclude you from doing that,” said Leggit. “It’s a matter of being smart.”