Water, Hydration, and Exercise

Facts about water and the human body

About 70% of the Earth’s surface is covered in water, yet the majority of people aren’t getting enough of it! Human beings, plants and animals need water for survival.  It is the most important nutrient for life and it accounts for 60 to 70% of the human body (it is the base of all the fluids of the body, including blood and digestive fluids). If water is so important for good function, good health and effective exercise, it’s a shame that we take it for granted.

Water serves a number of important functions within the body:

  • It is a lubricant that surrounds every tissue and cell of the body.  It is a transport medium in which nutrients can be transported to the cells.  It is also the medium in which waste materials are removed from the body.
  • It is necessary for numerous chemical reactions in the body, especially metabolic reactions involved in energy production.
  • It is a structural part of body tissues (i.e. proteins and glycogen).
  • It is extremely important in the regulation of body temperature.  If the body is not cooled properly through sweating, severe metabolic consequences can occur, including death.


Dehydration is a decrease in total body water, which occurs any time that fluid the body takes in doesn’t keep up with the fluid it loses.  Approximately 75% of people are chronically dehydrated, even if they are not physically active.  It doesn’t take much to become dehydrated.  The average adult loses approximately ten cups of water each day from sweating, eliminating waste, breathing and other routine functions.  We lose about two cups of water just by breathing alone.  Even becoming mildly dehydrated (1 to 2% of your body weight) can effect your body’s ability to function effectively.

Exercise and physical activity can have significant effects on your body’s hydration levels because of increases in your body’s temperature. To function properly, the body must maintain a temperature of 98 to 100 degrees (F). The body does this through sweating (when the body is too hot) and shivering (when the body is too cold). When exercising, the body can lose anywhere from 0.75 to 2 liters of water per hour. This can have negative effects on your performance and your overall health if you do not rehydrate effectively.

Symptoms of Chronic Dehydration

It’s important to identify chronic dehydration and take steps to reverse the condition.  When water in the body becomes scarce the body limits the amount it loses through breathing which includes the production of mucous, less frequent urination, decreased amounts of perspiration, and less frequent bowel movements and constipation.  Other symptoms include:

  • Headache, dizziness or lightheadedness
  • Dry, itchy skin
  • Acne
  • Nose bleeds
  • Repeated urinary tract infections
  • Dry, unproductive coughs
  • Constant sneezing
  • Sinus pressure

Most people end an exercise session in a state of dehydration that must be corrected by eating and drinking during the post exercise period.

Hydration Tips When Exercising

When exercising, it is always best to begin in a well hydrated state. The National Association of Athletic Trainers (NATA) recommends that you drink:

  • 16 to 20 ounces of water 2 to 3 hours before exercising
  • Another 8 to 10 ounces of water 10 to 20 minutes before exercising
  • 8 to 10 ounces of water every 10 to 20 minutes during vigorous exercise

These are simply guidelines to follow and not suitable for everyone.  The best way to tell if you are drinking enough water during exercise is to weigh yourself before and after exercising.  A one pound weight loss is equivalent to 16 ounces of water.

So, if you are one of the 75% of people who are not well hydrated, what steps are you going to take to ensure that your body is functioning at its best?

Written by TodaysFitnessTrainer (trainer@todaysfitnesstrainer.com).

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