We had a lot of discussion about fluid and electrolyte loss after running in the heat today. My fingers were starting to swell. That is a danger sign for me. Let me summarize what I know about it.
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.
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.
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.
| 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.
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.
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 long race. If blood sodium falls to less than 2,500 mg/liter, the result can be death. That, fortunately, is very rare.
Many athletes, like runners, 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.
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.
Dale Ruth
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