Maintaining proper electrolyte levels in endurance athletes is critical to performance.

by Kevin Setnes and Karl King

Kevin Setnes is an ultra runner, regular contributor to Ultra Running magazine and coach. Karl King developed SUCCEED products for endurance athletes. For more information, go to


Recent debates about the need for electrolytes raise many interesting questions and points. Too much or too little? What is right for you? Are there dangers to watch out for? These are valid questions; but there aren’t any yes or no answers.

Fact: Maintaining proper electrolyte levels in endurance athletes is critical to performance. There should be little debate here. Understanding an individual’s requirements is another matter.

Every athlete needs to understand his or her nutritional needs. Some things are basic: the need for fluids, the need for calories, and the need to pace yourself according to your abilities. Each athlete’s success will largely be determined by how well he/she understands his or her needs and abilities when attempting to go long distances.

Moderation should be one of the golden rules of all ultradistance athletes. Practice it in everything you do, until you fully understand your personal needs as an athlete. With electrolyte replacement, you need to know your fitness level, your sweat rate, the weather conditions, and the content of the replacement you are taking. Practice your electrolyte replacement in training, and continue electrolyte replacement in ultracycling events.

Hydration and Electrolytes

We’ve been told for years how important it is to drink during long distance events to avoid dehydration that degrades performance and can ultimately lead to a DNF or even collapse.

What we seldom hear is that we need to pay just as much attention to our electrolyte stores during an ultradistance event. Electrolytes are those salts which play a major role in the biochemistry and physiological processes of the human body. While dehydration is a serious problem, we see many cases of DNFs and death-march experiences because of electrolyte imbalance. You will enjoy your event far more if you take care of your electrolyte needs, as well as your hydration.

Let’s review where fluids are in the body, and their amounts. 60% of body weight is water. 40% of the body weight is inside body cells. 15% is in the space around the cells, and 5% is in the blood. Although the weight of the blood is minor, its water and electrolyte content are critical for good performance. Athletic performance suffers greatly with increasing dehydration.

Water is lost through: the skin/sweating, the lungs/breathing, urination, defecation (possible diarrhea ), vomiting and wounds. Except for the lungs, all those routes are also pathways for loss of electrolytes. The amounts of electrolytes lost in sweat and urine vary depending on fitness, body electrolyte content and acclimation to heat levels. Vomiting and diarrhea can lead to large electrolyte losses and are serious problems during an ultracycling event.

Weight Loss Consequences
0 to 2 % beginning thirst, performance loss at 1.8%
2 to 3 % thirst, 7% performance loss
3 to 6 % cramps, strong thirst, 20% performance loss
> 6 % severe cramps, heat exhaustion, coma, death

Sodium and Potassium

These are the major body electrolytes. The fluid in body cells is high in potassium; 90% of the body’s potassium is inside the cells. Other body fluids are high in sodium.

Fluid Sodium Content Potassium Content
Blood 3,100 – 3,330 mg/L 137 – 200 mg/L
Sweat 575 – 1,725 mg/L 155 – 200 mg/L

The major route for sodium loss is sweat. Because potassium is held inside the cells, it is not lost at high rates provided there is adequate sodium in the body.

Normal sweat rates can range from 0.75 to 2 Liters/hour, depending on conditions such as temperature, humidity, pace, clothing, and the degree of heat acclimation the rider has. A rate of one Liter/hour is not uncommon for an acclimated cyclist. At that rate, typical electrolyte loss rates by sweat are 1,300 mg/hr for sodium, and 230 mg/hr for potassium.

Electrolyte Imbalance

The body is sensitive to the amount of sodium in the fluid outside the cells, and in the blood. If the blood sodium level falls much below normal, a serious condition called hyponatremia is the result. The typical symptoms are: headache, muscle cramps, weakness, disorientation, apathy and lethargy. Those are often seen in the latter stages of an ultra. If blood sodium falls to less than 2,500 mg/liter, the result can be death. That, fortunately, is very rare.

The body has mechanisms to retain sodium when it is faced with sodium losses, but there is only so much compensation that can be done. If you keep sweating without replacing the salt losses, the eventual result will be electrolyte imbalance.

Because an athlete will be losing/ingesting both water and salt during an event, the situation can be complex. The body is sensitive to the ratio of sodium to water; the ratio can be raised or lowered depending on the rate of intake, and loss of both sodium and water. It is possible to see athletes in the same event who are suffering from different forms of electrolyte imbalance.

Many athletes, like triathletes and cyclists, will drink too little water and suffer dehydration. The athlete’s body usually cannot absorb water from the stomach as fast as it is sweated out of the skin, so most of them end up with some dehydration in an event. Some back of the pack cyclists may have enough time to drink more water than they lose, especially if they are moving slowly. Most ultracyclists will not fully replace the sodium they lose and have a deficit. Some of these athletes may take electrolyte supplements, some may use a sports drink with electrolytes, some may take salty chips or pretzels, and some may take no electrolytes at all.

Some may drink a mineral-free water in the latter part of the event and get dilutional hyponatremia even though they were fine earlier.

Since most distance athletes are not physiologists or biochemists, we won’t get deeply into the science, but let’s look at what commonly happens in an ultracycling event when insufficient electrolytes are taken.

Early in the event, sweat rates and sodium loss rates are high. Urination amounts may be high too. As sodium levels fall, the body increases the level of the hormone aldosterone that influences kidney function to slow sodium loss. As exercise continues and sodium is lost, blood pressure may fall. The body produces the hormone vasopressin to help maintain blood pressure. If exercise continues, with more water and electrolyte losses, performance begins to suffer and athletes slow down. Since sodium is important for the absorption of food and water from the digestive tract, what the cyclist eats and drinks is not absorbed. Nausea results. Even the sight of food may make one want to retch. This is your body’s way of telling you “Don’t bother because I can’t process it even if you force yourself to eat.” If you drink, the water won’t be absorbed well and will slosh around in the stomach. What is absorbed cannot be retained and will soon be urinated out.

As the level of sodium in the blood decreases, the ratio of sodium to water decreases to dangerous levels. As a defense mechanism, water will be moved from the blood into the spaces around body cells. That is why hands and feet can swell after many hours of competing.

Loss of water from the blood stream is equivalent to further dehydration, causing additional loss of performance. Such conditions lead to a DNF or misery all the way to the finish line.

A plan to avoid the problems

First of all, you can reduce your tendency to lose sodium by what you do when not training or competing. You can reduce the amount of sodium in your daily food. That will increase the level of aldosterone so that your body retains sodium better. Choose less salty foods. Use Morton Lite Salt in your salt shaker. That will reduce sodium and increase your potassium intake ( as will eating fruits and vegetables ).

If you expect to compete in the heat, get heat acclimated as soon as possible. That will reduce your sweat rate under hot conditions.

While you train, stay cool so that your sweat rate is lower. Wear light clothes, keep your jersey wet, and/or put ice on your neck.

Consume supplemental salt or electrolytes during the event. Most sports drinks have sodium levels that are fine for shorter distances, but inadequate for longer distances. Most gel products have insignificant amounts of sodium.

To satisfy your needs in a hot event you can take sodium in different forms. The simplest is table salt (a pinch per hour ). If an aid station has salt and boiled potatoes, you can dip a potato into the salt before eating it. V-8 and tomato juice are also good sources.

You can use an electrolyte replacement supplement, but check the sodium content. Some riders take salt tablet such as Thermotabs. Some athletes use Stamina Electrolyte Tablets but those are not a good source of sodium or potassium (they are a good source of calcium and magnesium ). Some athletes use SUCCEED! Buffer/Electrolyte Caps that are formulated specifically for ultradistance athletes such as cyclists, triathletes and runners to supply sodium, buffers and sufficient amounts of potassium.

As always, you need to drink. Don’t wait until you are thirsty; the human thirst mechanism is too slow and inaccurate. As the adage goes: Eat before hunger, drink before thirst.

When you finish a long training ride or event, you will usually have a deficit of water, calories and sodium. You will have a much smoother recovery if you replace all of those promptly. Soon after finishing, you can take an electrolyte supplement, 200 calories of carbohydrates and drink water until you are no longer thirsty, and are urinating again. In the days that follow, you will probably find that you have more energy and fewer aches and pains if you have promptly replaced water, carbohydrates and sodium after your long ride.