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When you’re exercising outside during the summer months, heat can be a significant factor affecting your stamina, endurance, and health. One important way to make sure you’re getting the most out of your workouts and not taxing your system needlessly is to pay careful attention to your hydration.

Exercising in the heat without adequate hydration can cause a number of issues, including fatigue, weakness, heat cramps, and heat stroke. Not only is dehydration bad for your health, it can also decrease your athletic performance. According to one study, losing just 2% of your body weight in fluid can result in a 25% drop in your athletic performance.

How to Stay Hydrated

Obviously, hydration is a serious issue, but it’s not as simple as drinking a certain amount.

Conventional wisdom says you should drink six to eight 8-ounce glasses of water per day, but that’s only a general guideline. We lose approximately 10 cups of water per day through basic bodily functions including sweating and urination, and you should be drinking enough fluids to replace the liquid you’re losing.

When you’re exercising in the heat, that amount can vary depending on a number of factors, including your weight, the temperature and climate, your physical condition, and the duration and intensity of the exercise.

Here are some hydration guidelines:

  • Find your ideal fluid intake. Calculate your ideal fluid intake by multiplying your weight by 0.5—that gives you the total number of ounces you should be drinking per day under normal conditions. For example, if you weigh 180 pounds, you should be drinking 90 ounces per day, which equates to 11.25 8-ounce glasses or 2.8 quarts.
  • Add more for exercise and heat. Exercising causes you to lose even more water than normal, both through sweating and breathing, so when you’re working out, you should add 12 ounces of water to your ideal daily intake for every 30 minutes you plan to exercise. If you are exercising in hot weather, you should add even more.
  • Space out your hydration. If you’re exercising, drink 15-20 ounces of water one to two hours before you start your workout, another 8-10 ounces 15 minutes before you begin, and 8 ounces every 15 minutes for the entire duration of your exercise. If it’s hot and you’re sweating heavily, drink more.
  • Don’t wait for thirst. Thirst is actually a sign of dehydration, so if you are experiencing thirst, you are already in a water deficit. More extreme signs include headaches and dizziness.
  • Monitor your urine. If you are adequately hydrated, you should be urinating once every two to four hours and the color of your urine should be clear or very pale yellow.
  • Be aware of your sweating. If your water deficit reaches 5% of your body weight, you will start to sweat less, which hinders the body’s ability to cool itself and can cause body temperature to rise dangerously.
  • Weigh yourself before and after exercise. One of the best ways to determine how heat and exercise is affecting your hydration is to weigh yourself immediately before and after your workout. For every pound lost, drink an additional 16-20 ounces of fluid.
  • Think twice about sports drinks. Drinks with added sugar, sodium, carbohydrates or other additives aren’t really necessary for most people—in most cases water gives you all the hydration you need. If you plan to exercise continuously and strenuously for longer than an hour, sports drinks can give you an energy boost and replace electrolytes lost in sweat.


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