Staying Well Hydrated: The Importance of Fluids During Exercise

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  • 0:01 Body Water
  • 0:50 Dehydration
  • 1:43 Heat-Related Illnesses
  • 4:16 Hyponatremia
  • 4:56 Staying Hydrated
  • 5:45 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Staying well-hydrated during exercise will help prevent dehydration, as well as the heat-related illnesses: heat cramps, heat exhaustion and heat stroke. Learn how to hydrate with the right fluid and sodium balance to avoid hyponatremia in this lesson.

Body Water

Did you know that more than half of your body weight is water? Body water is found in all types of tissues. It's in your blood, your organs and even in your bones! It's so abundant because it's so important.

The water inside your body lubricates your joints, keeps your body temperature steady and provides a medium to move nutrients around your body and remove wastes. With all of the services water provides, it's easy to see why you need to stay well-hydrated. This need is especially important during exercise, which causes the loss of water through sweat and increased evaporation from heavier breathing. In this lesson, we will examine how the loss of water during exercise affects your health and performance, and what you need to do to stay hydrated.


I'm sure that you have noticed that you feel thirsty when you exercise. While thirst is a sign that your body needs water, if you only drink enough to satisfy your thirst, it might not be enough to replace the amount of water lost. This could lead to dehydration, which is a condition in which the body has lost an excessive amount of water. Even a mild case of dehydration can adversely affect your exercise performance.

If dehydration worsens, it can decrease your blood volume. This makes it harder for your body to deliver oxygen and nutrients to your muscles, further diminishing your exercise performance. This lowered blood volume also diminishes blood flow to your skin, making it harder for your body to release heat. As your core body temperature heats up, your risk of suffering a heat-related illness goes up.

Heat-Related Illnesses

While heat-related illnesses do not always progress in a predictable way, it might help you to understand them if we follow a novice runner named Joe Beginner as he participates in his first long distance road race, which just happens to take place on a hot summer day. Joe was nervous on the morning of the race and forgot to drink water. His mouth was a bit dry, but for the first few miles he chose not to drink any fluids for fear that the added water might weigh him down. Those were not good decisions, and it's not long before Joe's body becomes dehydrated.

Suddenly, Joe is struck by a heat cramp in his leg that forces him to slow his pace to a walk. Heat cramps are painful muscle spasms that occur during and after exercise. The involuntary muscle jerking and cramping is caused by the loss of water and electrolytes, which are mineral salts, such as sodium. The losses cause an imbalance of electrolytes that interferes with the normal muscle contractions in Joe's leg. Fortunately, heat cramps are usually brief episodes, so in a few minutes Joe is off again.

However, he really should have had a drink because as he continues to sweat and lose water through respiration, his blood volume continues to drop. It's now getting hard for his body to cool itself and deliver sufficient oxygen and nutrients to his muscles. He has now moved into heat exhaustion, which is an overheating of the body characterized by excessive sweating and a rapid pulse. Joe is not feeling good and should take his feelings of dizziness and disorientation as signs to stop exercising, move to a cooler environment and get a drink, but he can see the finish line is just a mile ahead and he wants to cross it.

This decision to ignore his body's warning signs is not a good one as he is now on the verge of having a heat stroke, which is a life-threatening condition characterized by a lack of sweat, a high core body temperature, disorientation and hot, dry skin. Joe's core temperature has risen to 104 degrees Fahrenheit because his temperature-regulating mechanism is no longer working, which explains why his body stopped sweating. He does not get to cross the finish line as he needs immediate medical treatment.

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