Fluid and Electrolyte Physiology

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Focus Notes: Fluid and Electrolyte Physiology

In this topic we discuss how knowledge of fluid and electrolyte physiology is crucial to ensuring that an athlete’s health and performance are optimal during training and competition.

Role of Water

Question: What are the key roles that water plays in an athlete’s body?

Response:

Role of Water

Balancing Water Gain and Loss

• The athlete must regain fluid balance by replacing water and electrolytes lost during the sweating process.

• Water balance depends on the net difference between water gained and water lost.

• Because endurance athletes are particularly at risk for excessive loss of water during exercise, encourage athletes to carefully monitor their hydration status and replenish fluids to meet physiological needs.

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Focus Notes: Hydration Status

There are two simple methods an athlete can use to monitor hydration status: body weight and urine color.

Fluid Loss

Daily water balance depends on the net difference between water gained and water lost.

Athletes gain water from the consumption of foods and fluids.

Question: What are some of the causes of fluid loss?

Response:

Instructor Note: One study found that during an IRONMAN, the average athlete’s sweat rate for the bike leg is .81 Liters per hour, with ranges from .47–1.08 Liters. The average sweat rate for the run is 1.02 Liters per hour with ranges from .4–1.8.

Sodium (Download Resource)

99% of sweat is water; the other one percent is electrolytes. Sodium is an especially critical

electrolyte, particularly for endurance athletes with a high sweat rate, because compared to the other electrolytes, it has the highest concentration in sweat.

Question: How many milligrams of sodium can an athlete with a normal sweat rate loose per liter of water?

Response:

Hydration Status Description Body Weight

Urine Color

Instructor Note: One teaspoon of table salt has approximately 2,000 milligrams (mg) of sodium.

Sodium and salt are not interchangeable. Dietary salt, or table salt, is only made up of 40% sodium.

The other 60% of salt is chloride.

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Focus Notes: Other Important Electrolytes

Potassium, magnesium and calcium are also important electrolytes that are lost in sweat

• Potassium controls fluid and electrolyte balance, assists in the conduction of nerve transmission and helps move glucose into the cell.

• Magnesium regulates muscle relaxation and aids electrolytes through the cell membranes.

• Calcium plays a role in skeletal muscle contraction, nerve impulse transmission and the synthesis and breakdown of muscle and liver glycogen.

Factors that Affect Fluid Needs

Consider the following conditions when creating a customized hydration plan.

Factor How Does This Affect Fluid Needs?

Sport

Skin & Clothing

Environment

Heat Acclimatization and Altitude

Level of Fitness and Diet

Body weight, Gender

& Age

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Focus Notes: Fluid and Sodium Needs for the Triathlete

Question: What are some of the benefits of trying difference fluid replacement drinks during training?

Response:

Instructor Note: Remember: If an athlete is having issues with hydration, he or she should seek professional advice from either a licensed sports dietitian, nutritionist or a qualified healthcare provider.

Use the forward arrow to continue.

Guidelines for Fluid and Sodium Needs

There are general guidelines that can help provide a starting point for a hydration plan for your athlete.

Timing Guidelines for Fluid and Sodium Needs

Before Exercise

During Exercise

After Exercise

Instructor Note:

• The amount of fluid intake, as well as the rate of intake, will depend on the individual’s tolerance, the type of activity and the intensity of the activity.

• It is important to consume the fluids slowly, rather than all at once.

• Consuming beverages with sodium will help stimulate thirst as well as retain fluids.

Instructor Note: Consuming fluids in excess of sweat rate should be discouraged.

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Focus Notes: Sodium and Electrolyte Guidelines (

• Before exercise: consume beverages with sodium (460-1150mg/Liter) and/or sports nutrition products and sodium-containing foods to help to stimulate thirst and retain the consumed fluids.

• During exercise: consume 500 - 700 mg sodium per Liter or 32 fl. oz.

• After exercise: consume foods and fluids that contain sodium to facilitate rehydration.

This results in less urine production and improved hydration.

Sports Drinks and Nutrition Products

Sports drinks typically contain 500mg–700mg sodium per liter (33 fluid ounces).

Trial and Error During Training

Encourage athletes to use trial and error to determine the quantity of sodium and fluids needed for optimal performance.

Factors Affecting Fluid Absorption (

through the intestines to be moved into the cells. Any factor that reduces gastric emptying time and intestinal absorption will negatively affect the athlete’s performance.

Share this resource with your athletes when discussing the training and racing hydration plan.

Instructor Note: Remember: These are general guidelines. The amount of sodium per hour should be customized based on the athlete’s sweat rate and the average sodium concentration in sweat.

Instructor Note: Remember: Athletes having issues with hydration should seek professional advice from a licensed sports dietitian or nutritionist or a qualified healthcare provider.

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Focus Notes: Calculating Sweat Loss

Sweat rate calculations determine how much fluid an athlete should consume during a training session by calculating the amount of fluid that is expelled through sweat during exercise.

Sweat rate is specific to the discipline being tested, so athletes should conduct this test for swimming, biking and running.

Sweat Rate Calculations

To gather the information needed to determine sweat rate, the athlete will need to have an hour to exercise as well as have access to a scale.

Step 1. Before Exercise

Before exercise, the athlete should;

• void all urine and

• weigh-in wearing little to no clothing (this is done to obtain the most accurate reading).

Step 2. During Exercise

During exercise the athlete should

• work out, expelling moderate to high amounts of energy and

• monitor the quantity of water consumed.

Step 3. After Exercise

After exercise, the athlete should

• towel off and

• step onto the scale again (making sure to wear exactly what was worn before).

Instructor Note: You can find the Calculating Sweat Rate resource in the course module or in the Resources section. This resource covers how to calculate sweat loss. Use this as a companion resource as you continue through the next few screens of the course. You may also use this to determine the sweat rates of your athletes.

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Focus Notes: Rehydrating after Exercise

To adequately rehydrate, athletes should consume approximately:

• 16 to 24 fluid ounces for every pound -or-

• 1.5 Liter per kg body weight lost during exercise.

Dehydration

Dehydration occurs when the body loss exceeds fluid intake. A certain level of dehydration is inevitable with long distance training and racing. Athletes who lose two percent or more of their body weight during exercise are at risk for suboptimal performance. Inadequate fluid intake may result in fatigue, GI distress, reduced blood flow, increased heart rate and sometimes death. Dehydration increases the risk for heat exhaustion and is a risk factor for heat stroke.

Causes of Dehydration

Dehydration can be mild, moderate or severe, with health and performance risks increasing with progressive dehydration. Dehydration can also be cumulative and add up over the training session or event. This is especially true when the interval between training sessions is inadequate to fully hydrate.

Engaging in vigorous exercise (especially in hot climates) with inadequate hydration is the most common cause of dehydration. Other common causes include

• intense diarrhea,

• vomiting,

• fever and

• excessive sweating.

Who is at Risk?

Due to the long duration of an IRONMAN 70.3 or IRONMAN, all triathletes are susceptible to dehydration. An athlete’s sweat loss adds up each hour over the course of a long distance race, often resulting in mild to severe levels of dehydration at the finish. Triathletes with a high sweat rate face a greater challenge, because they must minimize fluid losses during the event.

For the athlete, it is difficult to achieve fluid balance for a number of reasons.

• Maximal sweat rates usually exceed maximal gastric (stomach) emptying rates. There is a limited amount of fluid that can be emptied by the stomach and absorbed by the gut.

• Athletes tend to replace only 50% of the fluid lost in sweat.

Instructor Note: Athletes needing rapid and complete recovery from excessive dehydration can drink approximately 1.5 L of fluid for each kilogram of body weight lost. This is equivalent to 23 fluid ounce per pound of body weight lost.

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Focus Notes: Dehydration

Signs of Dehydration Signs of dehydration include

• thirst

• flushed skin

• premature fatigue

• increased body temperature

• faster breathing and pulse rate

• increased perception of effort

• decreased exercise capacity

Other sign (that may occur later) include

• dizziness

• dark colored urine

• chills

• muscle cramping

• increased weakness

• labored breathing during exercise

Physiologic Responses to Dehydration

The following are physiologic responses to dehydration.

• A decrease in blood volume, reducing the amount of oxygen-rich blood delivered to the brain and the muscle (This negatively impacts muscle function, energy production and mental/cognitive performance.)

• An increase in heart rate (Due to lower blood volume, the heart compensates by beating faster to circulate more blood.)

• An increase in perceived exertion of exercise

• An increased risk of gastrointestinal distress (This is due to a delayed stomach emptying.)

• An increase in the body’s core temperature, risk for heat illness, heat stroke and injury (This is due to the increased loss of sodium in sweat and reduction in sweat production.)

How to Treat/Prevent it

Mild to moderate dehydration can be reversed or at least halted by taking in more fluid and electrolytes. Severe dehydration needs immediate medical treatment. Therefore, athletes should do everything possible to prevent it from happening.

To prevent dehydration, athletes should

• monitor and replenish fluid loss,

• create and follow customized hydration plans, and

• adjust fluid intake when the athlete’s health, training location or training duration changes.

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Focus Notes: Hyponatremia

• Hyponatremia is a medical condition in which the concentration of sodium in the blood is lower than normal.

• Severe hyponatremia is a medical emergency.

• Athletes and coaches should become familiar with the signs and symptoms of hyponatremia as well as know how to prevent it from occurring.

Causes of Hyponatremia

The following are contributing factors to exercise-associated hyponatremia.

• Overdrinking of hypotonic fluids, such as plain water

• Excessive fluid intake* compared to sweat rate

• Excessive loss of total body sodium (due to sweat)

• Inadequate sodium intake during exercise

* It is important to note, this occurs with the intake of water or fluid replacement beverages.

Who is at Risk?

• Individuals with small body mass, and a large sweat rate are most at risk for hyponatremia. Because women tend to have smaller body mass, they are at greater risk than men to develop exercise-associated symptomatic hyponatremia.

• Endurance triathletes are also at risk due to the length of time exercising.

• Novice triathletes who are not lean, run slowly, sweat less or consume excess water before, during or after an event are at risk.

• Older adults may have slower renal responses to water due to their age and may be at greater risk for hyponatremia.

• Nonsteroidal anti-inflammatory drug (NSAID) use may increase the risk of development of hyponatremia during strenuous exercise by inhibiting prostaglandin formation.

• According to the ACSM, in longer endurance events, sodium losses can induce

hyponatremia regardless if the individual is overdrinking or under drinking, so replacing lost sodium is warranted.

Signs and Symptoms

The following characteristics are signs of acute exercise-associated hyponatremia.

• Weight gain

• Nausea and vomiting

• Headache

• Confusion

• Loss of energy and fatigue

• Restlessness and irritability

• Muscle weakness, spasms or cramps

• Seizures

• Coma

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Focus Notes: Hyponatremia

How to Treat/Prevent it

To prevent hyponatremia, athletes should make sure to adhere to the following practices.

• Calculating and monitoring fluid needs

• Using thirst as a guide

• Adhering to the prescribed hydration plan

• Consuming sports drinks and salty snacks

• Avoiding consuming an excess amount of sodium-free water

Dehydration and Hyponatremia

The combination of dehydration and hyponatremia is called hyponatremic dehydration.

In this condition athletes are dehydrated (fluid loss is greater than fluid replenishment) and have a low serum blood concentration.

Any athlete who experiences symptoms related to dehydration or hyponatremia should immediately stop exercising and seek medical attention.

Instructor Note: If an athlete is suffering from hyponatremia, they should immediately stop exercising and seek medical attention.