Water - a key factor in getting the most from physical training

  • Published
  • By 2nd Lt. James E. Brown IV
  • 71st Medical Operations Group Aerospace Physiology
VANCE AIR FORCE BASE, Okla. --  Water is essential for maximizing exercise performance. Your body needs water for nearly every vital metabolic function. A normal balance of water is needed to avoid dehydration.

Each individual's need for water depends on a variety of factors, such as the exercise type, duration, intensity, ambient temperature and age.

Two of the most common mistakes in hydration listed by the International Society of Sports Nutrition are waiting until the thirst sensation begins and trying to rehydrate during training once dehydration has already occurred.

A key strategy advocated by the ISSN is to drink plenty of water, 32 to 48 ounces, before training begins. It is best to drink a large quantity of water in the hours before training, not immediately before exercise.

During training, sweat rates can be from one half to 2 liters per hour. Replenishment should be 6 to 8 ounces of water every five to 15 minutes to reduce elements of dehydration and heat illness.

For exercise lasting more than one hour, a glucose/electrolyte solution may be useful for extending exercise endurance capacity, reducing fatigue, and improving exercise recovery.

Sodium chloride is the major salt lost in sweat with sodium being the most important electrolyte to replace, followed by potassium and magnesium. It is best to avoid hyponatremia, a condition in which plasma volume increases faster than the electrolyte concentration from ingestion of excessive amounts of water.

This usually occurs from drinking too much water without proper electrolyte balance during excessive exercise in the heat. In a study examining hyponatremia incidents in U.S. Army trainees, the majority of trainees who experienced hyponatremia had water intakes equal to or exceeding 2 quarts per hour.

Major symptoms included mental status change, nausea and seizures, with too aggressive fluid replacement practices cited as the cause prompting policy changes.

Sport drinks consisting of glucose/electrolyte solutions provide these electrolytes which may be beneficial with exercise lasting more than an hour and/or in hot environments.

Some of the available sports drinks may even contain some amount of protein, which research suggests may further extend exercise endurance. It also may increase the anabolic response of the body to the exercise stimulus.

Muscle glycogen synthesis post exercise is faster with protein co-ingestion alongside carbohydrates, with sodium increasing absorption rates of fluid entering the intestines as well.

All in all, evidence shows that entering exercise in a dehydrated state will significantly impact exercise performance. Do not wait till the thirst sensation to hydrate. Keep an eye on your fluid consumption throughout the day and keep electrolyte intake up if exercise is expected to last more than one hour, especially in hot environments.

Even though the hottest months of the year have passed, hydration is still a critical aspect to be aware of in the colder months of the year.

(Lieutenant Brown holds a bachelor's degree in exercise physiology and is a Cooper Institute certified personal trainer. Contact him at Aerospace and Operational Physiology, 213-7931.)