All exchanges of gases in the body occur over membranes moistened by water.Hydration is one of the most important factors in the ability to train and compete at the highest level. And for some reason, it continues to be one of the most challenging aspects to control and stay in tune with. Athletes of all disciplines, ages, and levels struggle with finding the proper balance to meet their needs. To better understand the needs of any given athlete, it’s important to realize the purpose of fluid in the body.
It is common knowledge that water plays a vital role in health and wellness and that water itself makes up a large portion of overall body mass. From 65 to 75 percent of muscle mass is water, and 10 percent of fat mass is water, leaving anywhere between 40 and 70 percent of overall body weight to be in the form of water weight, depending on body composition.
Water is found in various places within the body, and 60 percent is intracellular (fluid inside the cell) and 40 percent is extracellular (water found outside each cell). Extracellular fluids include plasma, fluid in the eyes, secretions in the digestive system, fluid around the spinal column, and fluid created by the kidneys and skin. Plasma makes up most (approximately 20 percent) of the extracellular fluid. When cooling the body, most fluid lost in the form of sweat draws from this extracellular plasma fluid. The amount of fluid in these various places will be in constant flux.
Other properties of water in the body include the following:
All exchanges of gases in the body occur over membranes moistened by water.
The delivery of oxygen and nutrients to working muscles and the excretion of waste in the form of urine and feces require water.
Water and various other components lubricate the joints and cushion the vital organs.
Water has an unalterable density, creating a structured environment for muscle and various other body tissues. Muscles and tissues therefore require water to maintain their size and integrity.
Water’s resistance to temperature change makes it ideal for withstanding both environmental and internal changes in temperature. If water changed temperatures easily, then exercise in hot temperatures would be impossible because of the body’s tendency to overheat. The same would be true for exercising in cold temperatures; the body would freeze too quickly. Having water as a main ingredient in the body is crucial for coping with many environmental factors it is faced with.
Euhydration, the normal state of fluid balance, ensures that all these functions continue to run smoothly and efficiently. If provided with adequate amounts of fluid in food and beverages, as well as electrolytes, a healthy working system will monitor and control the proper amount of fluid retained and excreted. Electrolytes, in the form of charged ions, establish an electrical balance between the interior and the exterior of every cell. In other words, they help the cells in the body retain the proper amount of fluid to balance losses. These charges then facilitate nerve impulses to activate and contract muscle fibers. It makes sense that this cascade of events is very important for exercise and performance, but it is also important that these electrolytes, specifically sodium, be in balance for survival. The intake of fluid without the inclusion of key electrolytes to replace losses can actually be fatal. Sodium, potassium, and chloride are the three primary charged electrolytes found in the cell and are all dissolved in bodily fluids. Sodium and chloride are the two key electrolytes in plasma and extracellular fluid that aid in fluid balance of the cells of the body.
Hydration needs will vary from athlete to athlete depending on individual factors. Aside from genetic variances, a few known trends are seen in various populations engaging in sport. For starters, female athletes typically have lower sweat rates than their male counterparts. This is largely due to less surface area or smaller body size. Another reason is a smaller amount of muscle mass generates less heat, requiring less fluid in the form of sweat to maintain adequate core temperature. On the contrary, some research indicates that women have a higher water turnover than men, resulting in more urine fluid loss and an increased fluid need to replace losses. Last, there have been more reported cases of hyponatremia in women than in men, which could be attributed to many factors, both physiological and psychological. Hyponatremia is excessive fluid intake without necessary electrolytes, causing a fluid imbalance (more about hyponatremia later in this chapter).
Age also plays a factor. With increasing age (greater than 65 years), a decreased thirst perception can lead to an increased overall risk of dehydration. Along with that, older athletes recover from dehydration and exercise more slowly than their younger counterparts, creating the need for adequate recovery time. Impaired health and function of the kidneys in older athletes could lead to water retention and high blood pressure. For age-group athletes, observed sweat rates are lower before adolescence than at a mature age. This should be considered, especially if exercise and competition will be conducted in hot and humid environments.
Factors of DehydrationIn the ideal world, euhydration will always be achieved during training, during competition, and throughout the day. However, to be realistic, some degree of dehydration will occur as a result of the imbalance between sweat losses and the amount of ingested fluid consumed in the effort to replenish those losses. Often endurance athletes are dehydrated at the onset of activity because of improper recovery from previous training sessions or events, lack of awareness of actual needs, or an effort to cut down on weight.
In response to the stress of decreased availability of body fluid, the body reacts by altering normal biological markers. This leads to increased core body temperature, increased heart rate, decreased stroke volume (amount of blood pumped with each beat of the heart), and increased perceived exertion (mentally, activity feels much more difficult). The greater the overall dehydration, the greater the degree of these stress alterations.
There is a general agreement, supported in many research studies of trained athletes, that reductions in body water need only be minimal to cause detrimental effects on performance. Walsh et al. (1994) reported that a reduction in body mass of as little as 2 percent resulted in a reduction in performance of up to 44 percent. A level of dehydration as great as 3 percent (caused by diuretics) produced a 3 to 5 percent reduction in 1,500- to 10,000-meter running times (Armstrong, Costill, and Fink 1985). A few more recent studies indicate that well-trained athletes tolerate hypohydration to a certain degree. Laursen et al. (2006) found that a body loss of up to 3 percent was tolerated in well-trained triathletes during an Ironman competition without risk of thermoregulatory failure. This percent reference range is merely an average of observed tolerance levels. The magnitude of the effect on performance is determined by many factors, such as environmental temperature, the current exercise task, and an athlete’s unique biological characteristics. All these factors working together, and not merely in isolation, have a negative effect on athletic performance.
To add to the altered body functions caused by dehydration, cognitive processing and levels of motivation may become affected. In the sport of triathlon, concentration is vital and can be degraded by dehydration and hyperthermia, the latter being shown to have a greater effect. The cognitive effects of dehydration include a hindrance of short-term memory, working memory, and visuomotor abilities. Long-term memory is greatly decreased in athletes with exercise-induced heat-stress dehydration (Cian et al. 2000).
When determining how much fluid you need, let’s start with sedentary people in order to establish a baseline. A sedentary person, in a nonstressful environment, requires approximately 2.5 liters of water daily. As stated already, this depends on size and body composition. Sedentary men need closer to 3 liters of water a day, typically because of greater body size and higher muscle mass, which has a higher water content. Sedentary women need closer to 2 liters. Fluid losses for these people average about 2 to 3 liters, with 50 percent of that fluid in the form of urine. In an active person, this percentage of water losses can easily be offset by sweat losses or, in a person living at altitude, respiration losses.
Active people in a warm, humid environment can easily need 5 to 10 liters a day depending on increased sweat and other cooling-method fluid losses. During intense exercise, the 2 to 3 liters lost in 1 day in sedentary adults can be lost in 1 hour in athletes. This amount of sweat will greatly vary from athlete to athlete, even when fitness level, exercise intensity, and environmental factors are similar. Typical sweat values for athletes vary greatly, due both to individual and temperate conditions. An Australian study observing the sweat rates of water polo players found an average rate of .29 liter per hour, whereas a study of tennis players showed a sweat rate of 2.60 liters per hour. Here’s a look at how different sports compare in terms of sweat losses (USDA 2010):
Male water polo athletes lost .29 liter per hour in training and .79 liter per hour in competition.
Male half-marathon athletes lost 1.49 liters per hour in winter competition.
Male and female Ironman athletes lost .81 liter per hour in a temperate bike leg and 1.03 liters per hour in a temperate run leg.
To keep your body working at its best, for triathletes especially, hydration is a link to all other pieces of the puzzle. Without it, they won’t fit together, and peak performance is out of the question. For that reason, you should follow hydration recommendations not only in competition but also in everyday training. Following are the recommendations for before, during, and after training and competition, with the goal of always supporting euhydration, or hydration balance.
As stated numerous times already, proper hydration is important from the beginning of activity. The goal of euhydration is to start the physical activity with normal plasma electrolyte levels, which can be achieved with sufficient beverage intake and normal food consumption. However, if recovery time after prior training sessions is suboptimal (less than 8 hours), then it is very common for endurance athletes to start the next session dehydrated. In this case, a vigorous preworkout hydration program is necessary before the onset of activity. For triathletes specifically, drinking enough fluid during activity is difficult because of accessibility or excessive losses outweighing ingestion. Proper hydration can improve thermoregulation by minimizing increases in core temperature, thereby decreasing sweat losses and improving exercise performance in the heat.
The American College of Sports Medicine (Sawka et al. 2007) recommends 5 to 7 milliliters of fluid per kilogram of body weight 4 hours before exercise. In general, 400 to 600 milliliters (13 to 20 ounces) is advised in this 4-hour preparation time. So a 165-pound (75 kg) person would multiply 5 milliliters by 75 kilograms (for a total of 375 milliliters) to determine the lower range and multiply 7 milliliters by 75 kilograms (for a total of 525 milliliters) to determine the higher range. This recommendation stands for an athlete close to the euhydration state. In the case that urine production is nonexistent or production is dark or highly concentrated, then additional fluid is recommended. Two hours after the onset of exercise, an additional 3 to 5 milliliters per kilogram of body weight is recommended. The same 165-pound (75 kg) person would need an extra 225 milliliters (3 ml × 75 kg) to 375 milliliters (5 ml × 75 kg) of fluid. By determining fluid needs before exercise, an athlete can be assured that urine production can occur and be eliminated.
Including electrolytes in preexercise fluid intake is important for longer training sessions, especially for athletes who sweat excessively. The addition of 500 to 1,000 milligrams of sodium (about a quarter teaspoon of table salt) per liter of fluid, or simply eating a small snack of salty foods, will be plenty to help the body prepare for exercise. Forgetting to include these electrolytes, especially when high sweat losses may occur, can increase the risk of hyponatremia. Attempting to hyperhydrate (by using glycerol or drinking too much water) with fluids that expand the extracellular and intracellular spaces will greatly increase the risk of having to void, as intestinal absorption will be limited. Little evidence on the physiological or performance advantage of hyperhydration has been shown in research. This hyperhydration substantially dilutes plasma sodium before the onset of exercise.
Again, the goal for hydration during exercise is to balance losses to maintain euhydration. The American College of Sports Medicine recommends a loss of no more than 2 percent of overall body weight in the form of fluid (Sawka et al. 2007). In addition, fluid losses are accompanied by electrolyte losses, which should be compensated for by the addition of sodium in a replacement beverage. Exactly how much fluid and electrolytes an athlete needs depends on individual sweat losses and exercise duration. For this reason, it is important for athletes to monitor sweat losses, especially for exercise sessions lasting longer than 3 hours. The longer the workout, the greater the chance that fluid and electrolyte replacement may be insufficient and lead to deteriorations in performance.
Recommendations for hydration during exercise stem from the amount of fluids lost during a set amount of time, which will vary depending on climate, level of fitness, acclimatization, prior hydration status, and workout apparel. With all this variability, simple recommendations are difficult to make. Observed sweat losses in athletes vary from .4 to 1.8 liters per hour of exercise. With this broad range, it is imperative that athletes monitor their personal responses to varying training situations and develop their own customized fluid replacement programs that prevent losses of more than 2 percent of overall body mass at the start of exercise.
A simple way to do this is as follows:
1. Before exercise, weigh yourself without clothing and equipment.
2. Monitor fluid consumption during exercise.
3. Weigh yourself after activity without clothing and equipment.
4. Determine body mass loss during exercise.
5. Add to losses the amount of fluid consumed during activity, as the amount of loss is an indication of fluid needs during a set time of activity.
For exercise lasting more than 60 minutes, the inclusion of carbohydrate in addition to sodium will not only replace fluid losses but also provide fuel for ongoing activity. The rate of fluid absorption is closely related to the carbohydrate content of the drink. Too much carbohydrate can slow absorption. The absorption of water through the intestine wall is greater in the presence of sugars and sodium. Carbohydrate and sodium sports drinks are absorbed more rapidly than water or sodium and water alone. The optimal carbohydrate concentration (grams of carbohydrate per milliliter of fluid), according to research, is 5 to 8 percent. Along with this, sodium concentration should be 10 to 30 millimoles per liter for optimal absorption and prevention of hyponatremia. For this reason, sports drinks are certainly beneficial for activities lasting longer than 60 minutes.
Although most triathletes are well informed of the necessity of hydration, logistical factors involved in the sport of triathlon can make fueling and hydrating more challenging. Fluid intake during the swim is most often impossible, and depending on how long it takes to get on the bike, athletes may start the second leg of the race in a dehydrated state. Proper hydration on the bike is then crucial, as the running leg of the race creates problems for carrying enough water to support needs.
When trying to balance fluid losses, it is important to realize that fluid is not lost only in the urine and sweat but also via respiration. Although relatively low in shorter triathlons, these losses are quite significant in an Ironman. In an observation study of Ironman athletes, fluid losses were estimated as 940 milliliters (32 ounces) per hour lost in sweat, 41 milliliters (1.5 ounces) per hour lost in urine, and 81 milliliters (3 ounces) per hour lost through respiration. Thus, it is crucial that these athletes work toward ingesting approximately 1 liter per hour of fluid for the duration of their race.
Replacing Sodium LossesSodium losses in sweat depend on the overall sweat rate and the concentration of the fluid lost. Sweat sodium concentrations typically range from 250 to 1,500 milligrams per liter. Given the variable sweat rates of different athletes, there is a large reference range for sodium needs. One thing is for certain: For a triathlete training and competing for numerous hours a day, sodium needs may be greater than realized. Athletes engaging in endurance and ultraendurance events may need to monitor their sodium intake and be conscious of replacing losses appropriately. In addition to sodium, other essential electrolytes may be lost. Next in line, in order of concentration in sweat, are potassium, calcium, magnesium, and chloride. Although these nutrients are essential in the diet, the amount lost in sweat does not warrant doses as high as the sodium content of sports drinks. In races lasting long enough to significantly deplete these electrolytes, solid foods should be used for replenishment.
Most of the dietary recommendations available for public reading address the sedentary population. In the 2005 dietary guidelines released by the U.S. Department of Agriculture, the recommendation for sodium intake was no more than 2,300 milligrams a day. Every 5 years the USDA updates these recommendations, and sodium was reevaluated and changed to 1,500 milligrams a day in 2010 to address the rapidly growing population living with various chronic diseases such as diabetes, heart disease, and obesity. The USDA estimated that the average American diet contained 3,400 to 4,000 milligrams of sodium.
A distinction must be made between the difference in needs of those with chronic diseases and those living the lifestyle of an endurance athlete. An endurance athlete’s diet is stereotypically “healthier” and includes less sodium than the diet of the average sedentary American. In reality, this is far from the truth. A diet containing only 1,500 milligrams of sodium a day would sustain an Ironman athlete for less than 1 hour of high-intensity activity.
The cycling portion of a triathlon is the best opportunity for optimizing fluid balance. Fluid is the most readily tolerated and available during this time. However, high-intensity activity slows absorption compared to at rest. In a study performed by Robinson et al. (1995), gastric emptying was limited to .5 liter per hour when exercising at intense levels. The excess fluid ingested remained in the stomach, leading to feelings of fullness.
Recovery after exercise is important for the health of the body as well as for preparation for the next training session. Training and racing in a hot and humid environment can put a lot of stress on the body. Effective rehydration after exercise is achieved only by replacing both fluids and sodium. In fact, water alone for hydration is less efficient.
The American College of Sports Medicine (Sawka et al. 2007) recommends replacing 150 percent of sweat losses in the form of fluid for complete rehydration. The extra amount above what is lost allows for the flushing out of fluid through urine production. The inclusion of sodium (more than 1,000 milligrams) allows for increased fluid retention and the restoration of fluid balance in the extracellular and intracellular spaces.
Sodium in sports drinks has its benefits, but palatability is a consideration. Too much sodium is often not palatable for many athletes. For this reason, it is often recommended that you try many different sports drinks to find one that both provides the nutrients you need for proper hydration and that you are inclined to drink so you will achieve the intended goals of recovery time.
Many athletes are familiar with the constant instructions to hydrate but often don’t consider why this is important or what the serious consequences could be if hydration is overlooked. Numerous published research findings show the importance of a certain hydration level for maintaining peak performance or preventing deteriorations in performance caused by sweat losses and dehydration. Adverse health effects can occur if the body’s natural method of releasing heat is impaired. Peripheral vasodilation, or increased blood flow at the surface of the skin, allows for heat dissipation, but it decreases blood flow to the central nervous system. Sweat production increases this heat dissipation but also increases the risk of dehydration. The presence of sodium in the sweat increases the risk of electrolyte imbalance. Given these various conditions, the role of fluid in the body of an athlete is vitally important.
Following is an overview of the possible conditions occurring as a result of chronic dehydration as well as the signs and symptoms to look for to identify the problem before it spirals out of control. These are listed in order of mild to severe.
Proper hydration should always be the goal, not just during training and competition but throughout the day as well. As already stated, when hypohydration, or underhydration, occurs, adverse effects on training and performance are quickly apparent. Without the ability to cool the body in a properly hydrated state, varying levels of heat illness can easily occur in prolonged intense activity or shorter high-intensity sports. This condition stereotypically occurs only in hot and humid climates, but realistically it can also happen in cooler, dryer climates.
A graded continuum of heat illness has been established, ranging from mild, to performance-inhibiting, to life-threatening conditions, such as heatstroke. It is difficult to say which athletes are more susceptible to heat exhaustion, and it is not confirmed that all mild forms will inevitably progress to heatstroke. Although research is still ongoing in this area, all endurance athletes should be aware of the signs and symptoms of heat-related illnesses.
Heat edema is classified by noticeable swelling around the feet, ankles, and hands. It can occur as a result of the body’s effort to dissipate heat away from the working muscles to the skin. This peripheral vasodilation leads to the accumulation of interstitial fluid in the distal extremities, such as the wrists, ankles, hands, and feet. Core temperature is not affected by this condition, but athletes should be aware of it, especially if they are predisposed to its development. Older persons and unconditioned athletes not acclimatized are at highest risk.
Heat rash is another condition that arises from the effort to remove heat via excessive sweating. Also referred to as “prickly heat,” heat rash develops when clothing obstructs the secretion of the sweat ducts on the skin, causing irritation of the epidermis. Common areas for this to occur are the trunk, groin, neck, and areas covered by a sports bra in female athletes. Generally heat rash has a rapid onset and presents itself frequently in athletes who sweat excessively and those with a history of its appearance.
Heat syncope is classified by feelings of weakness and dizziness that disappear quickly after resting, sitting, or lying down. Core temperature is normal. This condition typically occurs immediately after the completion of exercise. Hypotension, caused by rapid peripheral vasodilation, decreases blood flow to the central nervous system, causing fainting or mental confusion. This can also occur with prolonged standing after strenuous activity and changes in body position from sitting to standing after strenuous activity. Sudden stopping and standing allows for venous pooling. Lying down after experiencing these symptoms can quickly increase blood flow to the brain and relieve symptoms.
Heat cramps are classified by the onset of painful muscle contractions, often in the calf or quadriceps, that are alleviated by rest, complete recovery, and stretching. Core temperature is normal or slightly elevated. Muscle spasms or cramps are one of the earliest signs of heat illness noticed by athletes. These cramps typically appear after exposure to excessive heat without appropriate hydration and electrolyte repletion. In this condition, the muscle begins to spasm, resulting in rapid, painful contractions. Sodium loss has been shown to exacerbate these spasms, but the role that other electrolytes such as magnesium, potassium, and calcium play is not yet clear. Other possible causes of heat cramps are chronic dehydration and overstimulation of muscle contraction beyond what the trained muscle is accustomed to.
Heat exhaustion is classified by core temperature elevated up to 104 degrees Fahrenheit (40 degrees Celsius). Malaise, fatigue, and dizziness are classic symptoms, along with nausea, vomiting, headache, fainting, weakness, and cold and clammy skin.
Heatstroke is the most dangerous form of heat illness and is classified by core temperature elevated higher than 104 degrees Fahrenheit (40 degrees Celsius). The skin is hot to the touch, without much sweating. The athlete experiences an altered mental state and may even be unconscious. Irritability, ataxia (loss of coordination), confusion, and coma are all possible results. Given the severity of these symptoms, prompt recognition and treatment are vital for the best chance of recovery.
There are two kinds of heatstroke, classic and exertional, based on the underlying cause of the excessive heat exposure. Classic heatstroke occurs mostly as a result of environmental factors such as high ambient temperatures and increased humidity preventing evaporative cooling. Exertional heatstroke is more due to internal heat production by the contracting muscles in the body, usually in the case of strenuous activity. Despite the variations in their causes, the treatment of these two conditions is the same.
Excessive fluid intake without necessary electrolytes causes a fluid imbalance called hyponatremia. Hyponatremia is, in essence, a water toxicity. The low sodium concentration in the plasma creates an osmotic imbalance across the blood brain barrier, causing too much water to flow into the brain. This leads to brain swelling, causing symptoms such as headache, confusion, nausea, and cramping.
With the increase in popularity of ultraendurance sports (greater than 3 hours), the occurrence of hyponatremia in athletes is also on the rise. Typically, athletes are more concerned about dehydration and replenishing fluid losses in these events. Relying on water and sports nutrition products without an appropriate electrolyte load will eventually result in a dilution of electrolytes in the body, or hyponatremia.
The following groups are at higher risk of developing hyponatremia:
Athletes with high sweat rates, especially in hot and humid climates
Poorly conditioned athletes with highly concentrated sodium losses
Athletes consuming low-sodium diets
Athletes on diuretic medications for hypertension
Athletes ingesting high amounts of sodium-free fluid during prolonged exercise (greater than 3 hours)
Given the known functions of fluid in the body, such as maintaining the integrity of cell membranes and facilitating normal reactions in the working muscles, it makes sense that dehydration can be harmful to the health of the muscle at the cellular level. Rhabdomyolysis is a syndrome causing the breakdown and destruction of muscle fibers. It is most often seen in new exercisers, strenuous exercisers, and athletes who overexert themselves. Clinical evidence suggests that dehydration can increase the consequences of this condition.
Clinically, creatine kinase levels (up to five times higher than the normal reference range) and reported muscle pain are indicators of this condition. Dehydration combined with heat stress and novel training can induce serious health problems. Soldiers and service men (e.g., police officers) engaging in a sudden increase of activity—typically in the form of physical training—without proper hydration are frequently treated for symptoms of rhabdomyolysis. The condition can lead to renal failure, and treatment often includes hemodialysis. Fatal cases with complications of heatstroke, rhabdomyolysis, and acute renal insufficiency have been reported.
Proper hydration is necessary for all types of athletes to train and compete at their best. Replacing fluid and electrolyte losses before, during, and after training and competition will ensure that physical and psychological performance is not compromised in any type of environment. Just how much fluid and other nutrients, specifically sodium, are needed will vary from athlete to athlete. Realizing the importance of proper hydration will help triathletes assess and monitor their losses to help them create a personalized hydration plan that works best for them.