Water You Talking About: How to Properly Hydrate for Endurance Exercise Part I

by Bree West October 24, 2012

Importance of Water:

Simply put, dehydration is insufficient water in the body, or in other words, the loss of fluids and electrolytes that are required to maintain normal body function. Dehydration happens when the body loses more water than it takes in. As water is the most essential part of the human body, a human can survive for days without food, but not without water. Water is responsible for transferring nutrients, eliminating waste from the body, maintaining blood circulation and pressure, lubricating joints and tissue, carrying moisture to the skin, facilitating digestion, and regulating and maintaining body temperature by sweating. Because water has so many important roles, a lack of it in the body can have devastating effects on health and athletic performance.

Hydrating the body properly is especially essential to athletes, particularly distance runners, because even slight dehydration can have negative impacts on cardiovascular functioning. Water is a major component of blood, and blood is what carries oxygen throughout the body and to the brain. So, without proper amounts of water, the heart has to work harder to pump blood throughout the body. Water is also responsible for the cooling functions of the body that are so vital during athletic activity. When an individual exercises, more energy, in the form of ATP, needs to be created in order for the body to meet the activity demanded of it. Running the energy systems of the body causes heat to be created, and because the heat cannot be used by the body for energy, it has to be released. Therefore, the temperature of the body rises during exercise, and in order to get rid of the extra heat being created, your body secretes sweat, which is mostly water and electrolytes such as sodium. Sweat evaporating from the body during exercise is the main way heat is lost. Dehydration can also cause muscle fatigue, loss of coordination, and/or heat illness such as cramps, heat exhaustion, or heat stroke.

Factors that Influence Sweat Loss and How to Assess Individual Water Needs:

One size does not fit all when it comes to knowing how much fluid to consume during an endurance run. The following factors can have an influence on sweat loss:

  • Duration and intensity of exercise
  • Environmental condition
  • Type of clothing being worn during exercise
  • Body weight of the athlete
  • Genetic predisposition
  • Heat acclimatization state
  • Metabolic efficiency

Because these factors have an influence on sweat loss, it is important for endurance athletes to understand how to properly hydrate their individual body. There are three main ways of assessing individual water needs:

  • Thirst
  • Urine color test
  • Determine individual sweat rate

Thirst is a signal that the body is near or already dehydrated. According to some experts, thirst indicates pending dehydration and therefore is a measure to determine hydration status. They recommend drinking enough water that you stop feeling thirsty. Other experts disagree however, saying that by the time an individual is aware of thirst, he or she is one liter of fluid below what is needed. Thirst, therefore, is the least accurate or reliable method of the three.

The urine color test method examines the color of the athlete’s urine to estimate hydration status. Urine is collected from the athlete following the event, and generally if the urine is light colored it indicates that the athlete is sufficiently hydrated. The darker in color the urine is, the more dehydrated the athlete. However, because there are other variables that can affect urine color besides hydration status, such as the intake of vitamins, foods such as beets, and medications, the urine color test method is not the most accurate measure of hydration status.

The most accurate method of determining hydration status is to determine one's individual sweat rate. Put simply, the athlete should weigh themselves prior to and after exercise. This is best done in as little clothing as possible to get the most accurate numbers. Comparing the difference in weight from before and after exercise tells athletes the amount of sweat (water) lost during exercise, because fat loss is not as immediate. By knowing how much sweat was lost during exercise, the athlete can then determine what his or her individual fluid requirements will be to adequately rehydrate.

In part II on Friday we will discuss how to properly rehydrate before, during, and after exercise, and water versus sports drinks.

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