Ch.7 Water and Electrolytes

There are two major aspects to fluid balance that must be considered and understood:

(1) water volume (2) the concentration of solutes in body fluid.

The type and amount of fluid consumed prior to exercise depends on the athlete's goals and tolerances. Typical goals include the following:

- Being fully hydrated prior to exercise - If not fully hydrated, rehydrating to the greatest extent possible - Avoiding gastrointestinal upset - Consuming carbohydrate, if appropriate

Use these foods sparingly when trying to cut down salt intake

- Foods prepared in brine, such as pickles, olives, and sauerkraut - Salty or smoked meats, such as bologna, corned or chipped beef, bacon, frankfurters, ham, lunch meats, salt pork, sausage, etc - Salty or smoked fish, such as anchovies, caviar, salted and dried cod, herring, sardines, and smoked salmon - Snack items such as potato chips, pretzels, salted popcorn, salted nuts, and crackers. - Condiments such as bouillon cubes; seasoned salts; MSG; soy, teriyaki, Worcestershire, and barbeque sauces; prepared horseradish, catsup, and mustard - Cheeses, especially processed types - Canned and instant soups

Strategies to cut salt intake include:

- Select fresh, unprocessed foods. - Cook with little or no added salt. - Prepare foods with sodium-free spices such as basil, bay leaves, curry, garlic, ginger, mint, oregano, pepper, rosemary, and thyme; lemon juice; vinegar; or wine. - Add little or no salt at the table; taste foods before adding salt. - Read labels with an eye open for sodium.

The main function of blood flow is to deliver oxygen-laden blood to tissues, and the need for oxygen delivery is greatly increased during exercise, particularly in the exercising muscles

Blood flow also helps to control body temperature, and this thermoregulatory function is used to a greater extent during exercise in the heat. - A finite and relatively small amount of blood is available to fulfill both these functions, and exercise in the heat sets up a competition for this limited resource

Electrolytes involved in fluid balance

Cations - sodium - potassium - calcium - magnesium Anions - chloride - bicarbonate - phosphate - protein

Dehydration, or moving to a state of hypohydration as a result of fluid loss, can have an adverse impact on...

Core temperature and ultimately on exercise performance

The __________ acts as a gateway for water entry into the body, initially through the plasma.

ECF Because ICF exists in isolated cells, water must pass through the ECF compartment in order to reach cells. The ECF, therefore, acts as a gateway for water entry into the body, initially through the plasma.

Athletes who are concerned about the potential for a moderate potassium deficiency should...

Focus on consuming a variety of fruits and vegetables daily. - Self-prescribed potassium supplements are not recommended because of the potential for hyperkalemia (that is, elevated blood potassium concentration), which has been occasionally reported in bodybuilders

If the athlete consumes a typical amount of dietary sodium, there is little need for the fluid replacement beverage to contain sodium unless the exercise duration is more than 2 hours and there is a very high sweat rate.

In such cases, it is recommended that 1 g of sodium per hour be consumed - This recommendation is made for endurance athletes who sweat heavily and whose sweat contains a large amount of sodium

Water losses by ventilation can increase in environments in which the air is colder and drier, as more water vapor needs to be added to the inspired air.

Increased levels of ventilation as a result of exercise may also cause an increased insensible loss of water. - With each breath, the inspired (inhaled) air is humidified to protect delicate lung tissues from drying. Some of the water vapor that is added to the air is then lost with the subsequent expiration because all of the water is not recaptured before the air is exhaled from the body - Skin must be kept moist to prevent drying and cracking, and some of the water that diffuses into the skin is lost from the body --> Water loss by this mechanism may also increase in dry environments with low humidity.

Sodium intake by athletes varies, based on caloric intake and choice of foods.

Low caloric intake may mean lower sodium intake. - As caloric intake increases, sodium levels rise, so even an athlete who is careful about avoiding high-sodium foods

Intracellular fluid electrolytes

Potassium (major cation) and phosphorus (major anion) - This distribution is opposite that of the ECF and represents an important concentration differential for each ion. - Because of these concentration differences, there is constant pressure for sodium to leak into cells and for potassium to leak out of cells. - Normal intracellular and extracellular concentrations are maintained by the action of the sodium-potassium pumps located in the cell membranes, which constantly pump sodium ions out of the cells while simultaneously pumping potassium ions back into the cells.

tonicity

The ability of a solution to cause water movement - Although a number of substances are osmotically active, the tonicity of body fluids is due largely to the concentration of electrolytes, electrically charged cations such as sodium and potassium, and anions such as chloride and phosphate ‍

The movement of fluid occurs as a result of controlling the amount of water in the ECF and the osmolarity of the ECF...

The amount of water and the osmolarity in the ECF is controlled by water intake and loss, by sodium intake and loss, and by compensatory regulatory mechanisms in the kidney and gastrointestinal (GI) tract.

If exercise is to extend beyond 2 or 3 hours, sodium replacement should be considered along with fluid replacement, either in a beverage, as a supplement, or with salty-tasting foods.

The recommended amount is 0.5 to 0.7 g of sodium per liter of fluid - It should be noted that sports drinks are hypotonic to plasma and, similar to water, should not be overconsumed

The water that is found in ICF and ECF is not static...

Water can be added to or removed from these compartments, and although cell membrane barriers separate the various compartments, fluid moves between compartments relatively easily.

Consumption of large amounts of water very quickly (for example, 3,000 mL, or ∼104 oz, or ∼13 cups in 4 hours, as some slow marathon runners have done) can result in a state of hyperhydration that can actually be...

dangerous to one's health and can even result in death - The excess water dilutes the concentration of solutes in the extracellular fluid, particularly sodium, resulting in hyponatremia. - Before the kidneys have a chance to excrete the extra water, the reduced osmolarity in the ECF provokes a shift of water from the ECF into the cells, causing them to swell - Nerve cells, especially those in the brain, are particularly sensitive to this swelling and may cease to function properly, resulting in impaired brain function, coma, or even death.

Other electrolytes that may influence water distribution are...

potassium, calcium, magnesium, chloride, and phosphate

The _____________ __________ provides the major physiological mechanism for controlling fluid balance in the body via the production and excretion of urine.

renal system - The amount of renal water loss is highly variable and can be influenced by the amount of fluid and salt intake, renal function, the action of various hormones, and the consumption of compounds that have a diuretic effect.

What sensible outputs are variable?

urine, feces and sweat - Urine output can vary dramatically, but for the average person under homeostatic conditions, it is approximately 1,500 mL per day (∼54 oz, or 6 to 7 cups) - The amount of water in feces is variable, but loss by this route averages approximately 100 mL (∼3.5 oz) per day. - If an individual is not in a hot environment, sweating is minimal, and water loss by this mechanism averages approximately 100 mL (∼3.5 oz) daily.

The only route of intake for sodium is by...

ingestion through foods, fluids, or, under certain circumstances, salt tablets and supplements (sodium chloride), but sodium can be lost from the body by a number of different routes (for example, sweat, urine, feces - Similar to water, sodium is generally consumed in excess of the body's requirements, and the body relies on the renal system to excrete what is not needed.

Salt intake around the world

- The highest reported consumption worldwide is in northern Japan where intake of sodium is estimated to be more than 10,000 milligrams (mg), or 10 g, daily because of the salting and pickling of foods. - The average daily intake of sodium in the United States is approximately 4,200 mg (4.2 g) for men and 3,300 mg (3.3 g) for women.

Plasma volume losses up to _____________ can occur with prolonged exercise, and losses of this magnitude may compromise cardiovascular function and ultimately reduce exercise performance

10 to 20 percent - As explained earlier, an average adult male has approximately 2.8 L of plasma. A 5 percent loss would be approximately 140 mL (5 oz) of water, an amount that would not likely impair exercise performance

The sodium content of sweat ranges from...

10 to 70 mEq/L, with the average concentration of approximately 35 mEq/L - One mEq of sodium is equal to 23 mg of sodium, thus the upper end of the range, 70 mEq/L, is equivalent to 1,610 mg or 1.6 g of sodium per liter. **This rate and amount of sodium loss typically does not pose a problem for the athlete if the exercise duration is not over an hour or two.

Clinically, hyponatremia occurs when plasma sodium concentration falls below ___________

135 mmol/L (from a typical level of 140 mmol/L). - Exercise-associated hyponatremia is often characterized by a rapid drop to 130 mmol/L or below and is particularly serious when it drops rapidly and remains low. - If nerve cells, such as those in the brain, swell too much, they cease to function properly, which can result in symptoms of dizziness, confusion, seizure, coma, and even death

Fluid losses during exercise resulting in decreases in body weight in the range of ___________ percent are strongly associated with declines in endurance exercise performance, particularly when the exercise is being performed in a warm or hot environment.

2 to 7

In general, a loss of more than _____ (percent) of body weight can be detrimental, especially when exercising in the heat, because physical and mental performance are reduced

2%

There is good evidence to suggest, however, that a loss of less than ____________ of body weight as fluid does not reduce short-term anaerobic performance or muscular strength

3 to 5 percent - At this level of dehydration, however, performance in single bouts of high-intensity exercise that are increased in duration (past approximately 30 seconds) may suffer. - Performance may likewise be impaired in repeated bouts of high-intensity exercise (for example, intervals) when the rest duration is short

A _______________ dietary analysis can reveal if the athlete's sports beverage intake is appropriate or if it is displacing other foods or drinks that provide needed nutrients, such as vitamins and minerals.

3- or 7-day

On average, an adult's body is approximately...

60 percent water by weight, but individuals may range from 40 to 80 percent.

A state of hypohydration will result in an increased core temperature during exercise in the heat and even in normal ambient conditions.

A loss of only 1 percent of body weight as water can result in measurable increases in body temperature, and the greater the loss of body water, the greater the increase in temperature. - It is estimated that for every 1 percent of body weight that is lost as water, core temperature will be elevated 0.1 to 0.23°C

What is a more practical approach athletes can use to measure hydration status? What are some limitations to using this method?

Observation of urine color is more subjective and may not be as precise as laboratory measures, but it is a more practical approach that can be easily conducted whenever the athlete urinates - It is typically recommended that athletes observe the color of the first void (urination) of the day after awakening from a night's sleep - Urine color may be affected by diet (for example, consumption of beets), dietary supplements, or medications, which reduce the accuracy of a color test. - A lighter urine color in the 1, 2, or 3 range can be considered well hydrated, whereas a darker urine color in the 6, 7, or 8 range can be considered hypohydrated.

euhydration

"Good" hydration (eu=good); a normal or adequate amount of water for proper physiological function - Enough water is present to maintain osmolarity of the extracellular fluid, prevent large water shifts between compartments, and support critical processes such as cardiovascular function and thermoregulation - this optimal level of hydration is typically achieved by consuming fluids in excess of need and allowing the renal system to excrete the unneeded amount -hypohydration, euhydration, and hyperhydration refer to the current state of water in the body

The pre-exercise fluid intake strategy is different if the athlete is not euhydrated.

- A more aggressive approach to pre-exercise fluid intake is needed. - In addition to the rule-of-thumb recommendation outlined above, ∼3 to 5 mL/kg 2 hours prior is recommended. - Using the previous example, a 50 kg (110 lb) female might want to consume an additional 150 to 250 mL (5 to 12 oz)

Sweat rates for a sedentary individual vs. an athlete

- An adult who is performing usual occupational activities throughout the day in a temperate (normal room temperature) environment may lose approximately 0.1 L (100 mL or ∼3.5 oz) of water each day as sweat - Sweat rates in excess of 2.5 L (2,500 mL, or ∼89 oz, or ∼11 cups) per hour have been observed in athletes competing in team sports (for example, soccer) and in individual athletes engaged in prolonged endurance sports (for example, marathon running) in hot environments

What type of sport they engage in determines their needs and therefore their water goals

- As an example, a sprinter may drink only water during the warm-up period and while waiting for the competition to begin. - Athletes engaged in prolonged exercise may choose a carbohydrate-containing beverage because both carbohydrate and fluid are needed during exercise *Postexercise intake should reflect the water and nutrients lost during exercise, and beverages play an important role.

Exercise can result in water shifting between compartments within the body and in accelerated loss of water from the body...

- As the cardiovascular system adjusts to the demands of exercise by increasing blood flow and oxygen delivery, the increased pressure in the blood vessels results in some of the fluid leaking into the surrounding interstitial space. - This fluid is lost from the plasma, and plasma volume therefore declines slightly as the water shifts within the extracellular fluid compartments *. This decrease in plasma volume occurs within the first few minutes after exercise begins, with the amount being largely dependent on the exercise intensity. The decline may be up to approximately 5 percent of plasma volume if the exercise is intense.

As these athletes have become aware of the dangers of hyponatremia that may occur in these events, some have attempted to counter the sodium loss by consuming it in the more concentrated form of salt tablets

- Athletes who supplement with salt tablets during an Ironman™-length triathlon do not have significantly different serum sodium concentrations than athletes who consumed a placebo. - It bears repeating that this high level of sodium intake during exercise is for those events and conditions in which there is large sweat loss for prolonged periods of time, that is, several hours or more.

Sodium is regulated by the kidneys and can be either reabsorbed or excreted in the urine...

- Because sodium intake usually far exceeds daily needs, a large amount of sodium is excreted in the urine to maintain sodium balance. - Average urinary sodium excretion is approximately 1 to 5 g per day. - A small amount of sodium is lost each day in sweat and feces. This obligatory loss amounts to approximately 0.5 g (500 mg) per day.

Liquids that are cool are generally better tolerated than those that are warmer (although their coldness may have no noticeable effect on body temperature).

- Beverages that are cool or cold do encourage athletes to voluntarily consume on average 50 percent more fluid compared to warm beverages, and this additional fluid consumption may reduce dehydration by approximately 1.3 percent of body weight

Why were athletes in the past warned about caffeine consumption?

- Caffeine (found in caffeinated coffee, some soft drinks, and "energy" drinks) and theophylline (found in tea) increase urine output by increasing the blood flow in the kidneys and increasing sodium and chloride excretion --> water loss - Based on the current body of scientific literature, a daily caffeine intake for adults of ∼450 mg or less does not have a negative effect on fluid or electrolyte balance (cup of commercially brewed caffeinated coffee contains approximately 300 mg of caffeine) - Although it is no longer recommended that caffeine be completely avoided by adult athletes, it is prudent for athletes to be aware of their caffeine intake and reduce intake if excessive.

How is sodium intake recorded?

- Consumption can be reported as either sodium or salt intake (sodium chloride), which often causes confusion because these terms are not the same. - For most people in the United States, sodium is consumed in the form of sodium chloride (salt added to food), and this sometimes leads to the reporting of salt intake rather than sodium intake.

Light sweating vs. heavy sweating

- During light sweating, sodium and chloride are reabsorbed from the tubule of the sweat gland and are not lost in large amounts. - During heavy sweating, however, the sweat moves through the tubule at a rate that is too fast for substantial reabsorption, so sodium and chloride losses are proportionally greater.

The presence of any one of these factors may not provide sufficient evidence of inadequate hydration, but the probability increases with the overlap of two or all three factors.

- Each morning, athletes need to evaluate whether (1) they are thirsty (2) their urine is dark yellow (3) their body weight is noticeably lower than the previous morning. - If one of these conditions is present, then they may be hypohydrated; if two conditions are present, then it is likely they are hypohydrated; and if all three conditions are present, then it is very likely they are hypohydrated

Exercise challenges fluid homeostasis because of the critical role that body fluids play in thermoregulation (maintaining an appropriate body temperature...

- Exercise causes an increase in body temperature, and a major mechanism for lowering body temperature is the evaporation of sweat. The loss of fluid through sweat may have a large impact on fluid balance, in both the short- and long term In contrast to sedentary individuals, who can regulate their fluid balance easily, athletes may have a difficult time preventing dehydration and severe hypohydration. - These conditions can negatively impact training, performance, and health - It is not uncommon for body temperatures to rise to 39 to 40°C (102 to 104°F) during exercise, even in temperate climates

Factors affecting sweat rate

- Exercise intensity can influence sweat rate through its independent effect on core temperature. -- Increased exercise intensity requires higher energy expenditure, which results in a greater amount of metabolic energy being converted to heat. - Independent of exercise intensity, higher ambient temperatures result in higher core temperatures and, in turn, higher sweat rates. - The relative humidity, or amount of water vapor in the air, can also influence sweat rate and can make fluid loss by sweating more visible -- Increased water vapor in the air reduces the ability of sweat secreted onto the skin to be evaporated, and it is the evaporation of sweat, not just the process of sweating, that leads to heat transfer and effective thermoregulation. - Clothing, uniforms, and protective gear may further influence the rate of sweating by providing a barrier to heat loss. -- This type of clothing may provide an insulating effect, trapping more heat in the body, or it may adversely affect the evaporation of sweat by reducing the surface area of the skin that is exposed. - The training status of the athlete and the degree of acclimation to the heat are also important factors affecting sweat rate. -- Trained athletes will start sweating sooner as body temperature begins to increase and will sweat at a higher rate, so they have a greater potential for water loss through sweating --> that they have a more effective mechanism for controlling their body temperature.

The two major forces that result in the movement of water are fluid (hydrostatic) pressure and osmotic pressure.

- Fluid, or hydrostatic, pressure is created when there is a difference in fluid pressure between two areas. ex: the cardiovascular system uses hydrostatic pressure to move blood throughout the body. When the heart contracts, it squeezes the blood that fills it, increasing blood pressure --> increase in blood pressure creates the driving force to propel blood through the blood vessels in the pulmonary and systemic circulation.

Although the body has sensitive mechanisms to maintain fluid balance over time, it is possible to exceed the capabilities of these mechanisms in either the short or long term..

- In general, the amount of fluid consumed is not carefully matched to the body's daily needs. The usual overall strategy is to drink an excess of water, retain what is needed to maintain fluid balance, and excrete the excess. Deviations from this basic strategy can result in imbalances

Another source of water is a result of aerobic metabolism...

- In the metabolic pathway of oxidative phosphorylation, oxygen is required in the mitochondria to be the final electron acceptor at the end of the electron transport chain. Oxygen (O) molecules pick up the electrons in the form of hydrogen (H) molecules and are thus converted to water - Aerobic metabolism contributes approximately 350 mL (∼12.5 oz) of water each day. For the average adult in homeostasis, approximately 2,700 mL (∼96 oz, or 12 cups) of water are consumed or produced by the body each day via food and beverage intake and metabolism.

Water loss from the body is generally categorized as either insensible or sensible.

- Insensible refers to avenues of loss that are not normally noticed by the individual, including water lost through ventilation and through nonsweat diffusion through the skin. - The three major areas of sensible water loss are the fluid lost in feces, urine, and sweat

More than 2 hours of continuous exercise typically marks the transition when the use of fluids that contain sodium and carbohydrate becomes necessary and appropriate.

- It is possible for athletes engaged in prolonged moderate- to high-intensity exercise in hot environments to sustain sweat rates of 1 L to over 2 L per hour, resulting in substantial sodium loss (∼1.5 to 3.0 g per hour) - In such cases, sodium replacement should begin during exercise by consuming fluids containing sodium, salt supplement products, or eating salty-tasting foods. - The addition of sodium may also encourage greater voluntary drinking and may aid in the uptake of water from the small intestine.

Unfortunately, it is very difficult to match water intake with water loss when exercising in hot and humid conditions for several reasons...

- Most people will experience "voluntary dehydration" and will not consume enough fluid during the activity to match the amount of fluid being lost. - Even if athletes are encouraged to consume more fluid than they would likely take in of their own volition, the rate at which the water can be emptied from the stomach and absorbed from the gastrointestinal tract may be less than the rate of fluid lost due to sweating. - More intense exercise may impede gastric emptying, though, and delay the replacement of water and carbohydrate - Therefore, even if athletes are encouraged or even forced to consume fluids in a prescribed amount in an attempt to match fluid loss, a gradual fluid loss usually still occurs because intake and absorption cannot keep pace with loss. - It is not uncommon for athletes exercising under these conditions to lose 2-7 percent or more of their body weight during the activity

The amount of water in the body depends on a variety of factors, including body size, gender, age, and body composition

- People have more body water compared to those of smaller stature, - Males have more water than females because men typically have more muscle mass and less body fat than women - Body water percentage has an inverse relationship with both age and body fatness; it declines with advancing age and increasing body fatness.

Potassium, the primary intracellular cation, is consumed via foods and beverages or, occasionally, through the use of a salt substitute (potassium chloride).

- Potassium is abundant in unprocessed foods such as fruits, vegetables, whole grains, beans, and milk. - Low dietary potassium intake in the United States is a reflection of a low daily fruit and vegetable intake and the high intake of processed foods because processing results in substantial potassium losses. - Examples of foods with a high potassium content include bananas, orange juice, and avocadoes. - Potassium found in food is easily absorbed from the gastrointestinal tract (greater than 90 percent absorption).

Extracellular fluid electrolytes

- The major cation (positively charged ion) is sodium. - The major anions (negatively charged ions) are chloride and bicarbonate - In addition, there are some negatively charged proteins in plasma (for example, albumin) that are typically not found in the interstitial fluid, but the amount is small compared to chloride and bicarbonate - The two major subcompartments of the ECF—plasma and interstitial fluid—have a nearly identical composition and distribution of electrolytes

Although much attention is paid to exercising in hot and humid environments, substantial fluid loss can occur with exercise in cold climates as well...

- Water loss from ventilation is usually greater in cold environments because the air is dry (low relative humidity) and the body must add more water vapor to the cold, dry air that is inspired - Clothing that is sufficiently warm at rest may prove to be too warm during exercise or activity, resulting in increased sweating and fluid loss.

Because the renal system is the major physiological mechanism for regulating fluid balance, an analysis of urine can also provide information about hydration status.

- When an individual becomes hypohydrated, the amount of urine produced is often lower than usual due to water conservation by the body. - in the hypohydrated individual, the urine also has a higher specific gravity (concentration of particles), higher osmolarity, and a darker color. -- Urine specific gravity of ≤1.020 and urine osmolality of ≤700 mOsm/kg are considered consistent with euhydration

Osmotic pressure is measured in milliosmoles (mOsm)...

- When the number of particles (solute) is measured per kilogram of solvent, the correct term is osmolality - When measured per liter of solvent, the correct term is osmolarity *In nutrition and medicine, osmolarity is the standard term, whereas in exercise physiology, the term osmolality is more commonly used because osmolality is not affected by temperature

Different body tissues contain varying proportions of water.

- blood plasma is largely fluid and consists of approximately 90 percent water. - Muscle and other organ tissue can range from 70 to 80 percent water - bone contains much less water, about 22 percent. - Lipids are anhydrous; therefore, fat tissue contains very little water—approximately 10 percent.

The Food and Drug Administration (FDA) does not regulate energy drinks,

- they may have much more caffeine than soft drinks, which must abide by the FDA-mandated limit of 71 mg of caffeine per 12 oz. - There have been some case reports of seizures, cardiac arrest, and erosion of dental enamel, and the FDA has been asked to look into at least five reported deaths from energy drinks. - Energy drinks are not recommended for children, pregnant and nursing women, and those sensitive to caffeine.

A smaller degree of dehydration, in the range of ___________ percent of body weight, may be tolerated without adversely affecting exercise performance, particularly if the exercise duration is less than approximately 90 minutes and the athlete is exercising in a temperate environment

1 to 2

To precisely determine an individual's hydration status, the amount of total body water and the osmolarity of the plasma must be known.

1) Accurate measures of total body water are often determined using isotope dilution, most commonly deuterium oxide -- When a known volume of water having a known radioactivity level is consumed, it is diluted as it is absorbed and distributed throughout the water compartments of the body. After distribution and equilibration, a sample of body water can be taken and analyzed for its radioactivity. Total body water volume can then be determined from the degree of dilution of radioactivity. 2) The plasma osmolarity level associated with euhydration is 285 mOsm/kg - To determine this value, however, a blood sample is needed, as well as access to a clinical laboratory for analysis. - Although this method has been shown to provide an accurate assessment of hydration at a single point in time, it is not very practical or desirable for frequent monitoring because of the time, expense, and necessity for drawing blood

The addition of water to the body is primarily accomplished through the...

1) fluid content of beverages and foods consumed each day 2) secondarily through metabolism *Adults in the United States consume ∼20 to 25 percent of their total daily water intake via food, 35 to 40 percent from tap or bottled water, and the remainder from other beverages *On average, an adult will take in approximately 2,350 mL (∼84 oz, or 10.5 cups) of water each day from beverage and food sources

Regulation of urine volume

1) fluid intake is low 2) blood volume decreases and osmotic pressure increases --> receptors in the hypthalamus detect this 3) Posterior pituitary gland secrets ADH 4) Collecting ducts become more permeable 5) Water reabsorption increases --> lower urine volume 6) Blood volume increases and osmotic pressure decreases

Total insensible water losses average approximately...

1,000 milliliters (mL) or ∼36 oz (∼4.5 cups) per day for the average person.

The Dietary Reference Intake (Adequate Intake) for sodium for adults under the age of 50 is...

1,500 mg (1.5 g) daily. The Tolerable Upper Intake Level is 2,300 mg (2.3 g) daily. - These recommendations are made to the general population to reduce the prevalence of high blood pressure associated with aging. - Doesn't apply to individuals to sweat daily though

Hyperhydration refers to body water above that considered normal and is typically a short-term condition.

Acute hyperhydration can be achieved by consuming excess fluids, but the renal system usually acts quickly (within minutes to hours) to excrete the excess water by forming greater volumes of urine. - For example, a person who drinks 2 cups (480 mL) of water with lunch will usually need to urinate by the middle of the afternoon. - Consumption of certain osmotic substances, such as glycerol, along with excess water may slightly prolong the state of hyperhydration

The ICF consists of all the water contained within the trillions of cells in the body. Some cells have higher content of water than others.

All of these cells maintain their integrity because of their cell membranes, which separate the fluid inside the cells from the extracellular fluid - For example, myocytes, or muscle cells, may contain as much as 75 to 80 percent water by weight, whereas osteocytes, or bone cells, may consist of as little as 22 percent water.

Pre-exercise fluid consumption should begin at least 4 hours prior to training or performance, if possible.

Although the amount will depend on the individual, a rule of thumb is to consume ∼5 to 10 mL/kg of fluid in a 2-4 hour timeframe before exercise - For example, a 50 kg (110 lb) female may establish a goal of consuming 250 to 500 mL (∼8 to 16 oz, or 1 to 2 cups) of fluid before exercise.

What is the RDI for potassium?

An Adequate Intake (AI) for adults is 4,700 mg daily

However, there may be times that the carbohydrate concentration of the beverage may be greater than 10 percent...

For example, ultraendurance athletes may benefit from large amounts of glucose during competition because the need for carbohydrate is so great.

Many factors influence the amount of sodium in the diet, but the largest factor in industrialized countries is the consumption of processed foods at home and at restaurants

For the average American adult, processed food is the source of 77 percent of daily sodium intake. - The addition of table salt (that is, sodium chloride) to foods accounts for approximately 11 percent of daily sodium intake. - The remaining sodium (∼12 percent) occurs naturally in water and in foods such as milk, vegetables, and grains

Sodium-Containing Products Marketed to Athletes

Gatorade Endurance Endurance Formula™- 8 oz (240 mL) ready to drink; Sodium: 200 mg Potassium: 90 mg Gatorade Endurance, Gatorlytes™- 1 pouch (3.4 g) in 20 oz water Sodium: 780 mg Potassium: 400 mg Magnesium: 40 mg Lava Salts™ 1 capsule 166 mg Sodium chloride: 255 mg Sodium bicarbonate: 80 mg Sodium citrate: 75 mg Sodium phosphate: 50 mg Potassium chloride: 30 mg

Glycerol Loading

Glycerol is easily absorbed and distributed throughout fluid compartments in the body, where it exerts an osmotic force to attract water. - A typical glycerol-loading regimen is to consume approximately 1.2 g of glycerol per kg of body weight along with 26 mL of water per kg of body weight over a period of about 60-90 minutes before exercise. - A review of research studies of glycerol hyperhydration and exercise performance indicates that this strategy may result in beneficial physiological effects for exercise in the heat such as increased sweat rates, decreased heart rate and core temperature, decreased thermal sensation, thirst, and rating of perceived exertion. - athletes who are subject to doping control should realize that glycerol is now considered a banned substance by the World Anti-Doping Agency (WADA).

In most cases, water is sufficient for pre-exercise

However, sodium does help stimulate thirst, retain body water, and encourage people to drink more, so a pre-exercise source of sodium may be beneficial. - In addition, if the athlete has been sweating heavily in the preceding days, care must be taken to consume adequate electrolytes, particularly sodium and potassium. If obtained in a beverage, the recommended amount is 20 to 50 mEq/L, or 460 to 1,150 mg/L, of sodium - The amount and timing of the fluid ingestion prior to exercise should be determined on an individual basis during training by trial and error.

As triathletes sweat for long periods of time, they lose water and sodium, typically leading to acute body weight loss, dehydration, and an increased concentration of plasma sodium. How does hyponatremia occur then?

If athletes consume a large amount of fluid that is hypotonic, for example, water, the fluid is replaced but not the sodium, so plasma sodium levels become diluted, resulting in hyponatremia - Subsequent practice among triathletes has been to consume fluids with sodium during triathlons, although some "salty sweaters" may need additional sodium supplementation, such as "endurance formula" sports drinks and/or salt supplements. - Because of the tremendous individual variability, each athlete needs to determine the fluid and electrolyte replenishment plan that works to optimize race performance while minimizing health concerns

Under normal homeostatic conditions, the osmolarities of the ECF and ICF are the same, and there is no net movement of water if the concentration in either compartment changes, a fluid shift may occur...

If sodium increases in concentration in the extracellular fluid, water would move by osmosis out of the cells and into the ECF in an attempt to dilute the extracellular fluid and restore balance. - For example, heavy sweating can cause a large loss of plasma volume due to water loss, resulting in an increased concentration of sodium in the plasma. This stimulates movement of water out of the cells (that is, ICF) and into the plasma (that is, ECF), causing the cells to shrink --> dehydration - Conversely, if the concentration of sodium in the extracellular fluid is decreased, the osmolarity of the ECF would be less than that in the cells, and water would move by osmosis into the cells in an attempt to correct the concentration imbalance. The resulting movement of water into the cells would cause the cells to expand or swell

Assessment and Establishment of a Fluid, Electrolyte, and Carbohydrate Replenishment Plan

Is the Athlete Generally Euhydrated? - If yes, 24-hour fluid intake appears to be appropriate. - If no, total daily fluid intake should be evaluated and adjusted. What are the Athlete's Goals Prior to Exercise? - If euhydration only, water intake is sufficient. - If carbohydrate is needed, choose from a sports beverage, carbohydrate gel and water, and carbohydrate-containing food and water. What are the Athlete's Goals during Exercise? - If only fluid is needed, water may be sufficient. - If carbohydrate is also needed, choose a sports beverage or carbohydrate gel and water, or carbohydrate-containing food and water. - If sodium is also needed, choose a sodium-containing sports beverage, sodium-containing food and water, or a salt supplement. What are the Athlete's Goals after Exercise? - Replenish water, carbohydrate, and sodium as needed with a combination of foods and beverages.

Athletes may experience painful muscle cramps during or immediately after exercise, known as exercise-associated muscle cramping (EAMC)...

It has long been believed that such cramping is due to dehydration, changes in electrolyte concentrations, or both. - Therefore, athletes have been advised to hydrate properly and eat more foods rich in potassium, such as bananas. - The ingestion of 1 to 2 oz (30 to 60 mL) of pickle juice has also been recommended because of its high salt content. **Despite a widespread belief that EAMC in all athletes is caused by dehydration and electrolyte loss, the scientific evidence that supports this theory is rather limited

The plasma serves as the fluid transportation medium to transport red blood cells, gases, nutrients, hormones, and other substances throughout the body. Why else is it important?

It is a major reservoir of fluid and plays a critical role in thermoregulation, particularly for activity in hot and humid environments

Hypokalemia, a severe deficiency state, is defined as a blood potassium concentration...

Less than 3.5 mmol/L and would be a rare occurrence in an otherwise healthy individual. - Symptoms include muscle weakness and cardiac arrhythmias, which can be fatal. - Hypokalemia is NOT a result of low dietary intake of potassium because the amount consumed in food is high enough to prevent this condition. Rather, hypokalemia is a result of substantial potassium loss, usually through severe and prolonged vomiting or diarrhea or the use of potassium-depleting diuretic drugs without adequately replenishing potassium.

Excessive Dehydration May Impair Exercise Performance

Maximal aerobic power (V02max) and endurance performance are reduced when an athlete is hypohydrated - With a loss of 3 percent or more of body weight as water, measurable reductions in can be observed. - When tested in the heat, however, modest fluid losses of 2 to 4 percent of body weight can result in significant declines in maximal oxygen consumption -- A hypohydrated athlete exercising in the heat becomes fatigued more quickly compared to an athlete exercising in a euhydrated state -

Intake and Output of Electrolytes Involved in Fluid Balance

Sodium - Food, beverages, use of salt shaker; salt tablets; intake can be excessive - Sweat, urine, feces; sodium loss in sweat is generally low but can be substantial for some people ("salty sweaters"); sodium output in urine is typically high because of tight homeostatic control by the renal system; fecal losses of sodium are small Potassium - Food, beverages; occasionally the use of salt substitute; intake tends to be low due to lack of fruits, vegetables, and minimally processed foods - Small losses in sweat or feces; losses in urine tightly controlled by the renal system; atypical losses such as vomiting and potassium-depleting diuretic drugs can be dangerous Calcium - Food (both naturally occurring and fortified), beverages, supplements; many people consume less than is recommended - Small losses in sweat; larger losses in feces (unabsorbed calcium) and urine; blood calcium tightly regulated by several hormones, which affect absorption, retention, and excretion Magnesium - Food, beverages, supplements - Small losses in sweat and feces; most magnesium is lost via the urine; some diuretics increase urinary excretion Chloride - Found as sodium chloride in food, beverages, salt

What is the most important electrolyte in ECF?

Sodium is the most important electrolyte in the extracellular fluid because it exists in the largest amount and therefore has a large and direct effect on osmolarity. - The body must respond to changes in the amount of sodium in the ECF by adjusting water volume. An increase in sodium in the ECF will increase the volume of water, and a decrease in sodium will result in a decrease in ECF water volume.

Deficiencies of what electrolytes would be rare?

The chloride content of the diet can be reasonably well predicted from salt intake, and phosphorus is widely found in food. A dietary deficiency of either would be extremely rare.

Intake during Training and Performance

Typical goals include the following: - Replacing lost body water to the extent possible - Slowing dehydration to the extent possible (prevent excessive dehydration (that is, >2 percent of body water loss) and excessive changes in electrolyte balance) - Avoiding the overconsumption of water and other hypotonic fluids - Replacing sodium if losses are large or rapid - Consuming carbohydrate if appropriate

Replenishment after Training and Performance

Typical goals include the following: - Restoring lost body water to achieve euhydration - Replacing sodium and other electrolytes lost - Consuming adequate carbohydrate to fully restore muscle glycogen - Consuming adequate protein to build and repair skeletal muscle - Avoiding gastrointestinal upset

dehydration

The term dehydration refers to the process of losing body water and moving from a state of euhydration to hypohydration - dehydration and rehydration refer to the process of losing or gaining water

The ECF is further divided into subcompartments.

The two main components of the ECF are the interstitial fluid (approximately 80 percent) and the plasma (approximately 20 percent). - Approximately two-thirds of total body water is in the ICF, leaving approximately one-third in the ECF - The plasma is contained within the vascular system and is separated from the interstitial fluid by the walls of the blood vessels. - The interstitial fluid surrounds the cells and provides protection and an avenue for exchange with the cells of the body.

When there is a loss of body water, the majority of the water comes initially from the ECF, specifically from the plasma

Therefore, as body water is lost through heavy sweating, there is a gradual loss of blood volume, a condition known as hypovolemia. - Because sweat is hypotonic in relation to blood, fewer electrolytes and other solutes are lost in sweat in proportion to the amount of water lost - In this case, the plasma that remains is more concentrated, and its osmolarity increases. Both of these conditions may adversely affect thermoregulation and exercise performance.

Case studies of tennis and football players suggest that exertional heat cramps may be the result of rapid and large losses of fluid and sodium

Those who fall into this group, known as "salty sweaters," benefit from sodium-containing beverages during exercise and the consumption of an adequate amount of sodium and water after exercise - Adding salt to food, eating salty foods, and consuming beverages with sodium are all ways to replenish sodium before the next exercise session. Salty sweaters must closely match salt (sodium chloride) and fluid intake to sodium, chloride, and fluid losses on a daily basis.

Water can be lost via ventilation, insensible loss through the skin, sweating, and urine and feces. While water can be gained

Water can be gained by the body through the consumption of food and/or beverages, and as a result of metabolism.

What happens with a potassium deficiency?

With such low average intakes, it is likely that some adults in the United States will have a moderate potassium deficiency. - Such a deficiency is associated with increased blood pressure and increased bone turnover due to an increase in urinary calcium excretion. - However, a moderate potassium deficiency is hard to detect with laboratory tests because the blood potassium concentration will remain within the normal range (3.5 to 5.0 mmol/L)

A diuretic is a substance that increases urine output. All fluids can have a diuretic effect...

Water is a diuretic if a person is in fluid balance and ingests a large volume of water. However, the focus is generally on substances that exert a diuretic effect by a mechanism in addition to an increased volume of fluid. - alcohol has a mild diuretic effect because it inhibits the production of the antidiuretic hormone (ADH). - Nearly 200 herbs are known to have a diuretic effect. - Some diuretics are prescription medications (for example, Lasix™) and can block the reabsorption of fluid and/or electrolytes from the renal tubules.

It is recommended that athletes drink approximately 1.25 - 1.5 L (∼50 oz, or ∼6 cups) of fluid per kg of body weight lost, beginning as soon after exercise as is practical

Water is not as effective in achieving euhydration as a beverage that contains some sodium because sodium increases the body's drive to drink and results in a temporary decrease in urine output

Water content of some beverages

Water- 99%; Some minerals depending on the hardness of the water and traces of other compounds Coffee or tea (black)- 99%; Some minerals depending on the hardness of the water and traces of other compounds such as caffeine Sports beverages- 90-94%; Sugars Fruit juice- 88%; Sugars Milk 88-91%; (depending on the fat content) Protein, minerals, milk sugar, possibly fat

The concentration of solutes, or osmolarity, in a particular fluid is not static, and it can sometimes change relatively quickly...

When a fluid has a higher concentration of solutes compared to another fluid, it is said to be hypertonic. For example, when a person sweats heavily, there is a loss of water from the extracellular fluid and the ECF becomes hypertonic in relation to the intracellular fluid

In another example of the fluid shifts resulting from hydrostatic pressure, feet and ankles may swell if a person stands for long periods of time...

When a person stands upright, blood rushes toward the feet because of gravity. This increase in hydrostatic pressure inside the blood vessels in the lower extremities results in more movement of water to the interstitial spaces in the feet and lower legs, resulting in swelling, or edema

There are circumstances in which it is important to attempt to match the amount of fluid lost during exercise with appropriate fluid intake strategies...

When exercise duration is prolonged, environmental conditions are extreme, and fluid losses are expected to be high.

It is critical for performance that athletes remain well hydrated because the adverse effects of hypohydration may offset the benefits gained by having a higher aerobic fitness level or by becoming acclimated to the heat.

When hypohydrated, heat dissipation ability is impaired, resulting in higher body temperatures. - At the same body temperature (that is, same level of stimulus), the hypohydrated athlete will experience a decrease in whole-body sweating rate and a decrease in skin blood flow, which can substantially reduce the effectiveness of the two main avenues of heat loss. - In addition to the declining blood volume, fluid loss may also adversely affect body temperature through the increase in osmolarity of the blood. - The blood becoming hypertonic may have a direct effect on the cells in this region of the brain and their ability to maintain body temperature - The worst-case scenario of increasing core temperature and deteriorating thermoregulatory control is hyperthermia (abnormally high body temperature), which may lead to coma and death (for example, heat stroke).

Body temperatures will rise in both athletes, but the hypohydrated athlete will fatigue at a lower body temperature. Why does this happen?

When hypohydrated, thermoregulation is impaired, and the athlete cannot tolerate the same amount of increase in body temperature without fatiguing.

Hypohydration occurs initially in the ECF, which results in an increased concentration of solutes in the ECF due to a relative lack of water. Why do we use the term dehydration?

When water levels decline in the cells, the cells shrink, and this shrinkage may impair cellular function. Hypohydration may have severe adverse effects on exercise performance and thermoregulation, so athletes need to be especially conscious of ways to prevent excessive hypohydration. - The term dehydration is commonly used interchangeably with hypohydration, but it is more accurate to use the term dehydration to describe the process of moving from a state of euhydration to a state of hypohydration.

The American College of Sports Medicine (ACSM) position paper notes that recommendations to avoid dehydration and sodium deficits to prevent muscle cramps is based on...

consensus and usual practice - (that is, Evidence category C) not experimental evidence (that is, Evidence categories A and B).

During exercise lasting less than 2 hours, the athlete would need to pay more attention to...

fluid replacement to address the water loss through sweating than to sodium replacement. - Water works well as a fluid replacement beverage under these conditions. The duration is short enough that excessive electrolyte loss is not likely, and therefore electrolyte replacement is not a priority. - The duration of the activity is also within the range in which endogenous carbohydrate (that is, muscle and liver glycogen) stores are not likely to be depleted, so the inclusion of carbohydrate in the beverage for exercise of this duration is likely not a necessity. **However, if an athlete does choose to consume beverages that contain carbohydrate and electrolytes, they are not likely to pose any problems for the athlete, if the athlete is accustomed to these beverages and does not consume an excessive amount.

The ACSM/AND/DC Position Stand recommends as a starting point that marathon runners consume 0.4 to 0.8 L of fluid per hour.

it is further recommended that the lower end of the range would be more appropriate for slower-paced, lighter-weight runners competing in cooler environmental temperatures, whereas the upper end of the range would be more appropriate for faster-paced, heavier-weight athletes running in hotter, more humid conditions. - Guidelines have not been developed for sports other than marathon runners, but the principles used to establish the guideline for marathon runners do have application for other athletes.

If consuming carbohydrate, the carbohydrate content of the beverage should be...

less than 10 percent (≤10 g of carbohydrate in 100 mL of water) for more effective fluid replacement and thermoregulation - Carbohydrate concentrations greater than 10 percent may slow gastric emptying and fluid uptake if consumed during exercise

Sweat contains the electrolytes...

sodium, potassium, and chloride; small amounts of minerals such as iron, calcium, and magnesium; and trace amounts of urea, uric acid, ammonia, and lactate. - Of these, sodium is present in the largest amount

Transcellular fluids are found in specialized cells such as...

the brain and spinal column (cerebrospinal fluid), joints (synovial fluid), areas surrounding the internal organs, heart, and lungs (peritoneal, pericardial, and intrapleural fluids, respectively), eyes (intraocular fluid), and digestive juices. - Although these fluids play critical functional roles, the total amount of water contained in these fluids is small and generally stable, so these fluid compartments are usually not included in discussions of body fluid balance.

The potential effect of dehydration on performance, therefore, is highly dependent on...

the individual characteristics of the athlete, the demands of the exercise task, and the environmental conditions.

Although EAMC often occurs in conjunction with heavy sweating, dehydration, and electrolyte losses,

there is no strong evidence that athletes who experience cramping have significantly different levels of dehydration or electrolytes than athletes who do not experience cramping.

Weight loss that occurs as a result of a single exercise bout is likely due to fluid loss...

thus, changes in body weight can be used as a marker of short-term fluid loss and as a benchmark for subsequent rehydration. - Changes in body fat or lean body mass over time complicate the use of this marker, but daily weight loss or gain over the course of a single workout can be used to determine water loss, and therefore hydration status, with reasonable accuracy ex: One liter of water weighs approximately 1 kg (2.2 lb). If an athlete completes a hard workout lasting approximately 1 hour and loses 2 kg (4.4 lb) of body weight, it can be assumed that approximately 2 L of fluid have been lost (2 kg × 1 L/kg - Weight is easy to track, and when used in conjunction with other markers such as urine color, it may provide a reasonably accurate and practical method for monitoring hydration status *However, checking body weight every day may be detrimental if an athlete is struggling with disordered eating, an eating disorder, or anxiety related to degree of body fatness. These athletes may misinterpret a 1 kg (2.2 lb) weight gain as a gain in body fat and not an increase in body water.