Dehydration impairs athletic performance whenever body fluid level falls below 98% of normal. The primary cause of dehydration is sweat loss, an essential body process which facilitates the release of body heat into the environment. When athletes don’t replace what they lose in sweat, the physiological function of the body’s heat management system is compromised, placing both the athletes’ performance and physical well-being at risk.

The Dehydration Factors

Exercise Intensity

Since heat is a byproduct of muscular activity, when an athlete’s exercise intensity increases, so does internal body temperature. The athlete’s body then has to regulate that temperature by sweating more, meaning that the harder athletes work, the more sweat they will lose.


Elevated environmental temperatures activate the sweat mechanism and cause sweat rates to increase. The humidity of an environment also plays an important role by restricting the evaporation of sweat, which in turn restricts heat loss from the body.

Clothing & Equipment

Minimal, loose-fitting clothing helps promote heat loss by exposing sweat-laden skin to the air, allowing the sweat to evaporate more easily. Heavy clothing and equipment (e.g., football pads and helmet) can trap heat and sweat against the skin, forcing the body to produce more sweat to cool itself.


Heredity assures that every athlete sweats differently. Those athletes with a sensitive sweat mechanism experience a more severe response to changes in internal body temperature, which predisposes them to higher sweat rates—and higher risks of dehydration. At the other extreme, some athletes are very efficient sweaters, producing only enough sweat to cool their bodies effectively.

Fitness & Acclimatization

An athlete who is “more fit” will sweat sooner—and sweat more—than an athlete who is “less fit.” The same is true for athletes who are accustomed (acclimatized) to exercise in the heat.

The Negative Impact on Performance

Cardiovascular Response

Dehydration strains the cardiovascular system by reducing blood volume. For every liter of fluid lost during prolonged exercise, body temperature rises by 0.3°C, heart rate elevates by about eight beats per minute, and cardiac output (the volume of blood pumped by the heart per minute) declines by 1 liter/min.

Dehydration's Warning Signs

Sweat loss reduces blood volume and increases the concentration of sodium in the blood. This stresses the the cardiovascular system and contributes to a faster increase in body temperature. Dehydration results in a number of symptoms that are important to remember.

  • noticeable thirst
  • muscle cramps
  • weakness
  • difficulty paying attention
  • nausea
  • fatique
  • light headed or dizziness
  • headache
  • decreased performance

Don’t wait for the warning signs!

Dehydration’s warnging signs only occur when the body is already dehydrated.  An athlete’s best bet for peak performance is to drink to minimize weight loss during exercise but avoid over-drinking.


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