Fluids

Do you pass by water stations in road races or skip water breaks during practice because you are not thirsty? Have you ever felt fatigued, dizzy, or cramps while exercising in hot weather? If you answered yes to either of theses questions, read on to learn how important fluids are for optimal health and performance. If your answers were no, read on to make sure you are following fluid recommendations that will optimize your health and performance.

• Role in the body
• Role in the diet
• Dehydration
• Overhydration
• Pre, during, and post exercise hydration

Role in the body

Water is key to life. Humans can survive more than a month without food, but only a few days without water. Water is found inside and outside cells and circulates in the blood. Our body consists of about 60-65% of water; for a 150 pound person, this represents approximately 90 to 98 pounds of water.

Water plays many important roles in the body including:

Transportation

• Water transports glucose, oxygen, and fat to working muscles.
• Water transports waste products, such as carbon dioxide and lactic acid away from working muscles.

Body temperature regulation

• The body wants to keep a constant temperature of approximately 98.6ºF or 37ºC. If the body temperature increases to >106ºF or 41ºC, cells will die.
• Working muscles generate heat. In fact, the body can generate 20 times more heat when working, than when at rest.
• To prevent overheating, the body regulates temperature by sweating. Water absorbs heat from the working muscles and dissipates this heat to circulating blood and ultimately through the skin.
• Sweat evaporates from the skin, which cools it down. This cools down the blood and the rest of the body.

Urine

• Water transports and eliminates waste-products in the urine.
  • The darker the urine indicates a greater concentration of waste-products and less water -- this indicates dehydration.
  • Vitamin/mineral supplementation can result in dark urine. Since supplements of individual vitamins or minerals (i.e. Vitamin C, selenium or chromium) may contain more than the body can absorb, they are excreted in the urine.

Digestion

• Water is an important component of saliva and gastric juices, which help digest food.

Lubrication

• Water is a good lubricator of joints, organs, and tissues.

Role in the diet

Water comes from more than just fluids, it is a major component of many foods. In fact, it is estimated that 20% of our water needs are met through food, not fluids. Foods with high water content add volume but minimal calories to the diet. Thus, these foods high in water are known to promote a feeling of fullness. Fruits and vegetables are two food groups that have generally high water content. Even meat, bread, and dairy products contain some water.

Example of fruits and vegetables high in water include:

		The daily recommended fluid intake is 10 - 15 glasses (8oz/glass) depending on your age and sex. Females and younger people are at the lower end of the range while males are at the upper end of the range. Foods contribute 20% of the fluids so actual fluid recommendations are 8 - 13 glasses (8 oz/glass) daily. Focus on Fruits and Vary your Veggies to help with fluid intake.   Athletes have greater fluid needs related to the role of water in physical activity. Thirst alone does not adequately supply these fluid needs, it will only supply 50% of fluid needs.

Dehydration

Athletes need to stay hydrated for optimal performance. Many athletes drink when they are thirsty and fail to hydrate before they become dehydrated. Thirst is a biological indicator of dehydration; however, dehydration has already occurred when an athlete becomes thirsty. Even a small drop in body fluids (1% of body weight, or 1.5 pounds in a 150 pound person) can impair performance.

Causes of dehydration

• Inadequate fluid intake
• Profuse sweating
• Failure to replace losses after exercise
• Exercising in hot weather, regardless of fluid consumption
• Relying on thirst to hydrate

Dehydration, or excessive fluid loss, causes the blood volume to drop. This increases heart rate as it tries to compensate for the decreased blood supply to the organs. Muscle cramps, dizziness and fatigue are caused by dehydration and can increase the risk for injury.

Dehydration can lead to heat illness, which impacts physical performance. Signs of heat illness are:

• Headache, dizziness
• Nausea, vomiting
• Weakness, reduced performance
• Irritability
• Irrational behavior
• Inability to concentrate
• Fatigue
• Muscle Cramps
• Confusion/ disorientation

Signs of dehydration and heat illness directly related to performance include reduced muscular strength and endurance.

Note in the figure below that even a 2-4% loss of body water (3 - 6 pound loss for a 150# person) will reduce muscular strength and endurance. Studies have shown reduced isometric and isotonic muscular contraction of 20-25% with 4% dehydration. In addition, 24-36 hours are needed to fully recover muscular strength and endurance after dehydration. This is noteworthy because wrestlers commonly use dehydration to make weight.  This practice compromises their muscular strength and endurance and there is not enough time between weigh-in and competition to adequately rehydrate.

Urine volume and color are good indicators of hydration. A light colored urine indicates adequate hydration. In addition, a larger volume of urine indicates better hydration. Since vitamin supplements can make the urine darker, volume may be the better indicator for those taking vitamin supplements.

Prevention
It is important to adequately hydrate before, during and after exercising to prevent dehydration. Keep in mind the following factors that will influence your fluid needs:

• Altitude - Fluid requirements are greater at high altitudes.

• Climate - If the temperature is warm you will need to consume more water. Even during a cold day when you may not sweat as readily it is very important to hydrate.

• Sweat - Individuals who sweat easily and in large quantities are at greater risk for dehydration. Estimate your sweat rate per hour by weighing yourself before and after.

• If you lose 2 pounds in one hour you lose 32 ounces of fluid. This translates into a consumption of 8 oz of water every 15 minutes.

• To make fluid replacement easy, measure 8 oz of water and then count how many gulps it takes to drink. Then use the number of gulps as a guideline.

To get more information on individual sweat rates and estimate your sweat rate visit the Gatorade® Sports Sciences Institute (look in the upper right hand corner of the page).

• Type and length of activity - The intensity and length of duration of an activity will determine the need for fluids. Endurance athletes who exercise for hours will lose more water and may be more sensitive to dehydration for optimal performance than a sprinter. Swimmers may not feel the heat and the extent of sweating from exercise due to the cooling effect of the water, thus are at increased risk for dehydration. Wrestlers who dehydrate themselves before weigh-ins will impair their performance and place themselves at risk for health problems related to dehydration.

REMEMBER: Rehydration prior competition may not be adequate to replace the fluid losses. It takes 24-36 hours after dehydration to fully recover the muscular strength and endurance lost due to dehydration.

Overhydration (hyponatremia)

Although rare, overhydration, also known as hyponatremia, can occur in athletes. Athletes with a high concentration of sodium in their sweat, consume large/excessive quantities of water, or exercise long periods of time (4-6 hours) are at greatest risk for hyponatremia. Hyponatremia is a serious condition, which in worst cases can be fatal. Hyponatremia occurs when plasma sodium concentrations reach <135 mmol/L (normal levels are 138-142 mmol/L).

Hyponatremia can cause gastrointestinal problems (bloating, nausea etc.), wheezy breathing, swollen hands and feet, unusual fatigue, and incoordination. Life-threatening problems include swelling of the brain, which can result in throbbing headache, confusion, seizures, coma, and death.

Determine if you are at risk...

• Do you have high sweat volumes and high sweat salt concentrations?

• If you sweat large amounts and notice white salt on your skin, or if your sweat stings your eyes, the sodium concentration is high.

• Do you exercise for hours?

• Do you eat a low sodium diet and consume excessive amounts of water?

Be sure to visit the Gatorade® Sports Science Institute for more information, resources, and interactive tools on hydration.