Hyrdation and Exercise

Water makes up approximately 60% of your total body composition. In addition, 73% of lean body mass or muscle is composed of water. It is the essential nutrient for survival and is required for all cell functions. Water is also an important constituent in thermoregulation, because it is a major component of blood volume. It is mainly lost through sweat, respiration, and waste. However, when the body is dehydrated, most of the water lost is from the blood.

Sweat Basics
The average person has 2.6 million sweat glands. Sweat is made up of water and electrolytes such as sodium, chloride, and potassium. When the hypothalamus senses an increase in core temperature it will act by increasing blood flow to the skin, stimulating the sweat glands. The result is an increase in the rate of water lost through sweating.

During low- to moderate-intensity exercise of less than one hour, there are minimal electrolyte losses because the body reabsorbs most of the electrolytes from the sweat. However, during moderate- to high-intensity exercise of greater than one hour, the electrolyte loss in sweat becomes significant and the sweat rate is too fast for re-absorption of electrolytes.

Normal fluid and electrolyte loss in urine:

How much water is lost during exercise?
During high-intensity exercise, a person can lose up to 2.0 liters of water per hour! However, 1.0 liter of water per hour is more common. Sweat rate can vary depending on the environmental temperature, humidity, type of clothing worn during exercise, intensity of exercise, fitness level of the individual and acclimation of the individual to the environment. Replacing fluids during and after exercise is very important for staying hydrated and preventing dehydration. Signs of dehydration include dark colored urine (urine should be the color of water with a splash of lemon), muscle cramps, decreased sweat rate, and increased fatigue.

What is the best way to stay hydrated?
According the American College of Sports Medicine (ACSM), before, during and following exercise, water or a carbohydrate/electrolyte drink is recommended to stay hydrated. The drink of choice should be cold in temperature and taste good to the individual. If it’s more palatable to the person, more will be ingested!

ACSM makes the following general recommendations for the amount and type of fluid that should be ingested before, during and after exercise:

*Approximately 24 hours before exercise, an individual is recommended to consume fluids and foods to promote hydration. Fruits, vegetables, and carbohydrates are examples of foods that promote hydration. In addition, avoid too much alcohol and caffeine, as these fluids can cause water loss and promote dehydration.

*Two hours before exercise, 16 ounces (2 cups) of fluid should be ingested to promote hydration and allow time for excretion of excess water.

*During exercise of less than an hour, it is recommended to ingest water every 15 minutes to prevent dehydration. Electrolyte loss is negligible; therefore a carbohydrate drink is not necessary.

*During exercise of greater than an hour (60 min), it is recommended to ingest a carbohydrate and electrolyte drink every 15 minutes.

*Never restrict fluids during exercise! Quite the contrary. Encourage your students to take water breaks during the class. Many aquatic exercise professionals actually plan the hydration breaks into the structure of the class.

*After exercise ingest a carbohydrate and electrolyte solution. The carbohydrate will replenish glycogen stores (muscle carbohydrate stores) and the electrolytes will replenish sodium, chloride, and potassium lost in sweat. The addition of Trace Minerals B-12 maybe helpful to the chronic exerciser as well. In addition, avoid carbonated drinks, as they make you feel full and decrease fluid intake. Adding protein can reduce the amount of carbohydrate necessary to replenishing carbohydrate stores.

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