Basic Hydration for the Long Distance Runner

How do I know how much water or sports drink to consume during a run? The bottom line is, you need to drink just enough so you aren’t thirsty during your run. But for those who want facts, we compiled this article to help you get a better understanding of the definitions and science behind hydration for the average long distance runner.



What is hyponatremia? Hyponatremia is a low concentration of sodium in the blood

Most commonly seen in endurance athletes, hyponatremia is a potentially life threatening condition. Sodium plays an important role in water balance and muscle contraction and is a required element for normal body functions. The body has a remarkable ability to maintain its sodium and water balance. However endurance events, including marathons, challenge this critical survival mechanism.

Sodium is necessary to draw water through permeable membranes in the body and allows for distribution of those fluids throughout the entire body. Without adequate sodium, your body will no longer be able to move water across permeable membranes, causing dehydration. You can drink all the water you want, but if you don’t have the sodium necessary to move it from the gut to the bloodstream, you will become hyponatremic. Depending on the intensity and duration of exercise, hyponatremia can be life-threatening.

What causes hyponatremia? Fluid overload, sweating and medications

Drinking large amounts of fluids without replacing adequate sodium can lead to hyponatremia. Additionally, there is a relationship with the total volume of sweat lost during an exercise session and fluid replacement. Lost sweat (salt, other minerals and water) through prolonged exercise if replaced by water (with no salt) could produce diluted sodium in the blood stream which in turn can cause hyponatremia.

Climate also plays a role in the possibility of developing low blood sodium. In warm climates, like here in Florida, we sweat more per hour requiring an increase in salt replacement. The same results can occur in cool climates. The sweat rates are lower, but drinking too much fluid can decrease the concentration of blood sodium giving the same affect as if the athlete had sweat out too much salt.

Medications such as ibuprofen, aspirin, and other non-steroidal anti-inflammatory drugs can contribute to hyponatremia due to their interference with kidney function and their potential for masking heat exhaustion.

Who is at risk for hyponatremia? Endurance athletes and women

Studies have shown that endurance athletes are at risk for developing hyponatremia due to the fact that it is difficult to find a good balance between adequate hydration, over hydration and accurate sodium replacement during prolonged physical activity.

Women are at greater risk than men for developing hyponatremia. Women generally tend to be smaller in size than men and are more likely to develop fluid overload since it takes less fluid for small people to become overloaded/over-hydrated. Excess fluid retaining hormones in women have also been sited as contributing factors that prevent the female athlete from excreting excess fluids. The hormonal contribution to hyponatremia is still under debate.

Signs and Symptoms for Hyponatremia:

Slurred speech
Upset stomach
Hyponatremia in extreme cases can lead to convulsions/seizures, coma and death.
How can you prevent hyponatremia? Adequate fluid replacement with beverages containing electrolytes, determine individual rates of fluid loss and avoid using anti-inflammatory and/or pain relieving medications during exercise.

Anytime an athlete exercises for over 1 hour, electrolytes must be replaced to avoid hyponatremia. Although the exact amount varies it is generally advised that you should ingest 1 gram of sodium per hour during endurance activities. This varies by individual and can be difficult to accomplish. Athletes need to find a healthy balance and may need to increase their salt intake in the days leading up to a big race and know how much sodium is in their sports drinks. It is difficult to adequately replace lost salt during a hot race. It is likely that more salt will be lost through sweat than can be replaced, even when consuming sports drinks. Knowing your body and having a good balance prior to the event is key to avoiding hyponatremia.

Determining individual rates of fluid loss is a way to calculate how much sodium one needs to maintain a healthy system. You can do this by weighing yourself before and after a run to determine your sweat rate. The weight loss in ounces represents the approximate amount of fluid volume in ounces to be replaced by a sports drink. Though this method isn’t a completely accurate way to determine your fluids needs, it gives you a baseline to start.

Medications such as pain relievers and anti-inflammatory should be avoided during endurance activities, because they negatively affect our kidneys and can indirectly cause hyponatremia. One should always check with their physician prior to using these medications in connection with physical activity.

What is the treatment for hyponatremia? Inactivity and salt ingestion

Medical professionals will need to determine if an athlete has developed hyponatremia. In the event that no medical personal are available, inactivity is the first treatment. The body at some point will start to get rid of the excess fluid by increasing urine production. Salt will then need to be ingested over the next 10-12 hours. With medical staff present, diuretics are typically administered along with a high salt concentrated solution givenintravenously at a very slow rate.


What is dehydration? Dehydration is the loss of water and salts essential for normal body function

The basic premise behind dehydration is an inadequate intake of fluids resulting in the body losing more fluid than it takes in. The fluid/salt balance needed to maintain healthy cells and tissues can be seriously disrupted with dehydration.

Dehydration can occur in as little at 30 minutes of exercise, especially in hot weather. The body relies on sweating to dissipate the heat generated from working muscles. Sweating also helps to maintain our core body temperature. Allowing our core body temperature to be maintained within a safe range is a key element in preventing heat related injuries which may initially be caused by dehydration. The amount of sweating necessary to sustain heat loss during vigorous exercise inevitably will lead to dehydration unless adequate fluids are ingested.

Dehydration will diminish an athlete’s performance and can lead to death if not corrected. Dehydration is one of the most common factors for heat related sickness such as heat exhaustion and heat stroke. Both heat exhaustion and heat stroke cause numerous deaths each year.

Heat exhaustion is characterized by an increase in core body temperature and heart rate. People with heat exhaustion may also exhibit fatigue, weakness, dizziness, headache, nausea (sometimes vomiting), and muscle cramps.

Heat stroke is characterized by a very high core body temperature, reddened skin and the absence of sweating. Heat stroke is the most dangerous of the heat injuries and can cause a stroke and death if not corrected.

What causes dehydration? Not drinking enough fluids, strenuous activity, excessive sweating, vomiting, diarrhea and heat exhaustion

Strenuous activity such as running requires adequate fluid/electrolyte replacement or dehydration will occur. Excessive sweating due to climactic conditions and/or intensity of exercise can rapidly dehydrate individuals if corrective measures aren’t taken. Vomiting, diarrhea, fever, diuretics, illness, a variety of medications such as anti inflammatory’s, low fitness levels, sleep deprivation, lack of heat acclimatization, staying in the sun too long, not drinking enough fluids, and alcohol can all be contributing factors to dehydration.

Who is at risk for dehydration? Athletes (adults and children)

Adult athletes are at risk for dehydration, especially during the summer months, for any activity lasting longer than 30-60 minutes. Without proper hydration, the body can quickly lose water and other essential elements running the risk of kidney problems or even death. Children, due to their smaller stature are at an increased risk of developing dehydration. For all athletes, once dehydration starts, the deterioration can be quick.

Signs and Symptoms for Dehydration:

Excessive sweating
Thirst (this is not a good indicator, usually when the thirst mechanism is activated, dehydration has already occurred)
Dark colored urine
Reddened skin
Weak irregular rapid heart rate
Low blood pressure
General weakness
Rapid and shallow breathing

How can you prevent dehydration? Drink when you are thirsty before, during and after exercise. Wear proper clothing, be heat acclimatized and avoid certain medications.

The best preventative measure to ward off the possibility of becoming dehydrated is to stay hydrated. An indicator of hydration is not always an output of large volumes of clear, dilute urine. The only good indicator is not something we can easily measure – the concentration of your blood plasma.

Runners vary individually in what their body requires to stay hydrated. Some may only need 14 ounces of fluid every hour, while others may need 26 ounces. Replacing lost fluids during exercise when the duration is longer than 60 minutes, is recommended. Consuming 16 ounces of fluid replacement every hour of exercise is a good rule of thumb to follow, especially during endurance events such as a marathon or half marathon. Replacing fluids post exercise allows the body to hold onto the balance it seeks to achieve as well as aiding in muscle recovery, especially when the fluids contain carbohydrates and protein. Choose a sports drink that contains carbohydrate, electrolytes, and a small amount of protein. Mixing your water with half sports drink, helps your body absorb the fluid better than water alone. The process of your body losing carbs and fat during exercise, affects your overall hydration calculations, which makes hydration calculators not an exact measurement of what your body needs. Listen to your body, experiment during training, and run safe.

Proper clothing can influence your cooling efficiency. It is best to go with light colored clothes as they reflect light and in turn remain cooler than darker clothing. Choose materials that wick away the moisture, which allows for better air circulation, thus facilitating more rapid cooling. Cotton is not a good choice because it does not wick moisture away from the body.

Heat acclimatization takes about 10 days. Adapting to the heat helps our bodies make the necessary adjustments to promote better cooling.

Certain medications can cause dehydration by interfering with sweating, kidney function and diuretic effect. Check with your physician before beginning any exercise program.

What is the treatment for dehydration? Rapid cooling, re-hydration and seek medical treatment

Understanding the cause of dehydration is the first step towards treatment. If heat appears to be the cause of dehydration, rapid cooling is recommended. Cooling can be achieved by loosening an individuals clothing and moving out of the direct sun. Ice can be used if available and should be applied to the athlete’s groin, armpits and neck.

Rehydration or replacing lost fluids is essential in correcting dehydration. Salt and water work together to allow our bodies to achieve a healthy balance. The salt acts to draw water through permeable membranes, which aids in the distribution of fluids throughout the entire body. Too much salt however, can have a reverse affect, and pull too much water through the membranes and can lead to further dehydration.

When dehydration is extreme, the body stops sweating to preserve the remaining blood volume. As a result, our core body temperature will increase to dangerously high levels, causing a heat stroke. Heat stroke is a serious medical emergency and requires medical attention. Individuals require medical attention to correct this degree of dehydration and it may take 48-72 hours under supervised medical care to correct heat stroke. Heat stroke is life threatening.

What is a method for calculating the amount of fluid a person needs during exercise?

Individuals vary, which why we recommend drinking to satisfy thirst. Here is a calculator which can be used as a baseline while you experiment during training to figure out your specific hydration needs.

Baseline fluid requirements for non-exercising individuals can be calculated by weighing the person in lbs and dividing that number by 2:

• Wt (lbs) divided by 2 = minimum daily requirement of fluid for a non-exercising individual represented in ounces
• Example: 140 lb male
140/2 = 70

70 ounces fluid replacement necessary for daily maintenance

Exercising individuals need to build on the minimum daily fluid requirement. A method for determining fluid replacement for an exercising adult is by weighing themselves before they run and weighing themselves again after they run. The change in weight represents the approximate amount of fluid necessary to achieve a fluid balance.

• Example: 140 lb male
Pre-exercise weight: 140 lbs

Post-exercise weight: 139 lbs

• 1lb of weight loss = approximately 16 ounces of fluid to be replaced
This is in addition to the minimum daily requirement.

On hot days, your body will require additional amount of fluids. An athlete’s performance diminishes every degree over 50 degrees fahrenheit.

What are the differences between using a sports drink vs. water during exercise?

For all activities lasting less than 1 hour, water alone is adequate. During prolonged exercise, anything lasting longer than 60 minutes, the fluid replacement needs to match the specific substances lost with the increased duration of activity. Sports drinks have the capacity of replacing the body’s depleted supplies while contributing to muscle recovery. Sports drinks provide several advantages over water specifically by providing electrolyte replacement, carbohydrates to fuel our working muscles as well as aiding in muscle recovery. Important features of sports drinks are taste, carbohydrate and sodium content.

Sports drinks have the potential of restoring electrolytes lost during exercise, while prompting the desire to drink. The added salt and pleasant taste of sports drinks trigger the thirst response, encouraging consumption of fluids which in turn reduces the chances of developing hyponatremia and dehydration.

Carbohydrates are the primary fuel that powers muscles during exercise. Sports drinks containing 6-8% carbohydrate provide the energy needed to improve our muscles capacity for work. Many studies have shown that athletes consuming sports drinks containing 6-8% (6-8 grams of carbohydrate per 100 ml of fluid) carbohydrate can exercise longer with less fatigue than athletes that drink only water. There is a fine line however between the correct amount of carbohydrate for optimal fuel and energy and too much carbohydrate which can lead to bloating and nausea. In addition, when the carbohydrate content is too high, the rate at which fluid is absorbed into the blood from the intestine is slowed due to the delay in gastric emptying which can impede re-hydration. The rate of absorption and gastric emptying (how fast the fluid moves through the stomach into the intestines) varies per individual. Variations in the guidelines may be necessary for those who have difficulty ingesting and digesting high volumes of fluids with increased percentages of carbohydrates. In addition, studies now show a very small amount of protein in your sports drink, will help the absorption rate and retention of your fluids.

Sports drinks contribute to muscle recovery. Muscle recovery depends on how well the body recovers its glycogen stores and repairs muscle tissues after exercise. Current research shows that carbohydrate replacement, along with protein, 30-60 minutes after exercise can have an enormous impact on an athlete’s next day performance. During this one hour period of time, athletes consuming sports drinks restore about 50% more of their glycogen than those who did not consume sports drinks or replace their lost carbohydrates with simple sugars. An added advantage of drinking sports drinks during the recovery phase is that typically athletes appetites are decreased, causing a deficit in nutrition and fluid. Re-hydrating with sports drinks post exercise may be a more palatable way to replace lost nutrition during a time of suppressed appetite which will in turn speed recovery

Ingesting carbohydrates during prolonged exercise delays fatigue and enhances performance. Water alone is appropriate when an activity is less than 60 minutes. Any exercise lasting longer than 60 minutes requires electrolyte and carbohydrate replacement to increase energy, aid in muscle recovery and maintain adequate hydration. Athletes need to be well fueled, well rested and well hydrated for optimal energy and performance.

Consuming sports drinks before, during and after exercise have proven benefits by replenishing muscle carbohydrate stores and restoring lost body fluids.