Fluids, Electrolytes and Optimal Race Performance 

Dehydration, electrolyte imbalance, muscle cramps, and heat stroke are four good reasons why every athlete should understand the basics of fluid physiology. Quite simply, what you don’t know can be deadly. Let’s look at some facts and myths about balancing fluids and minerals correctly, and racing responsibly for the conditions.

Fluid Balance Basics

Q: I have heard that drinking as much water as possible the day before a race is a good way to make sure your body is fully hydrated for racing. Is this true? 

A:  The amount of fluid and sodium the body retains is carefully controlled by the kidneys. In order to maintain a certain level of sodium in the bloodstream, the kidneys will release extra water as urine if the sodium level becomes diluted and falls. Excessive amounts of sodium-free fluids such as water will ultimately mean more trips to the bathroom and may cause sodium levels to fall too low if a large volume of water is ingested over a short time period. The kidneys will gradually begin to retain more sodium so that balance is restored. This gradual readjustment works fine while the athlete is at rest. During exercise, however, sodium loss may be significant. Symptoms of sodium depletion (known as hyponatremia) include excessive fatigue, bloating, confusion, and disorientation. Blood levels of sodium that drop too low can lead to coma, seizures and death.  

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Q:  I read that additional sodium in the days leading up to an event may be a good way to stockpile levels so you're not depleted on race day. 

A:  Most athletes get plenty of salt (or sodium) in their usual daily diet. However, during periods of acclimatization to hot temperatures, sodium losses may be higher than normal. To ensure adequate sodium intake to cover losses in sweat, eating salty foods or adding table salt to foods is recommended. This does not mean you have to go crazy with the salt shaker the night before a race. A sodium load can rapidly increase fluid retention and may cause heart failure in susceptible individuals, as well as significant bloating. Research has shown that optimizing fluid reserves the day of the race can be done by consuming a meal with sodium about four hours before a race, followed by a beverage with a high sodium level about two hours before the onset of exercise.  

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Q:  If the race is “on,” can I assume it is safe for me to participate?

A:  Races are rarely cancelled due to the weather, and that includes a heat wave. If you haven’t been training in the heat, then your sodium loss will be about 50 percent higher than if you were acclimated to high temperatures. And if you are not in shape for the race and have not been training in the heat, you will lose almost twice as much sodium per liter of sweat. Being trained and acclimated for conditions is a critical factor when it comes to tolerating exercise stress in a hot environment. Race responsibly, and know your limits. 

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Q:  Does pickle juice relieve muscle cramps because it is high in sodium?   

A:  A 2 ½-ounce dose of pickle juice brine has been shown to reduce the duration of muscle cramps. Why it works is still a matter of debate. However, studies have shown that the sour tasting juice does not change plasma sodium levels. Researchers speculate that the effectiveness of pickle juice in providing relief is possibly due to the effect of a nervous impulse stimulated by the vinegar on tired muscles.

Q:  Do I get muscle cramps during exercise because of low sodium or potassium levels?

A:  Despite the popular theory that exercise-induced muscle cramps are caused by sodium or potassium deficits, recent studies have suggested otherwise. The actual cause of muscle cramps is still hotly debated. But in a recent study on Ironman triathletes, researchers found there was no difference between athletes who cramp vs. non-cramping in pre-race or post-race serum electrolyte concentrations and body weight changes. Several studies have found that the development of muscle cramps was associated with faster actual race times, a history of muscle injury, or a history of previous muscle cramps. 

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Tips for Racing in Hot Weather

• Start exercise well-hydrate.
• Know how to dress for the weather.
• Consider alternate cooling strategies (besides sweat) such as an iced t-shirt, wet hair, or visor.
• Have a fluid and sodium-replacement plan.
• The longer the race, the greater the risk for sodium depletion.
• During exercise a sports hydration drink is the best choice. It should contain:
  
  • 180 mg – 200mg sodium per 8 oz
  • 20 mg – 50 mg potassium per 8 oz
  • 12 g – 24 g carbohydrate per 8 oz

• Practice drinking during exercise. A sloshing stomach indicates too much fluid is being consumed at one time. Drink smaller amounts more often.  

This joint position statement is authored by the American Dietetic Association (ADA), Dietitians of Canada (DC), and American College of Sports Medicine (ACSM): 

“Dehydration (water deficit in excess of 2-3% body mass) decreases exercise performance; thus, adequate fluid intake before, during, and after exercise is important for health and optimal performance. The goal of drinking is to prevent dehydration from occurring during exercise and individuals should not drink in excess of sweating rate. After exercise, approximately 16-24 oz (450-675 mL) of fluid for every pound (0.5 kg) of body weight lost during exercise.”

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Pre-Event Guidelines

4 hours before event

Eat a pre-race breakfast that is high carbohydrate, moderate fat and protein. Include some salty foods or add salt if using an unsalted food such as natural oatmeal or hard- boiled egg.  

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Some breakfast ideas:

1 cup instant oatmeal + ½ cup milk 647 mg sodium

English muffin +1 Tbsp peanut butter 273 mg sodium

Spinach, feta and egg white wrap 900 mg sodium

Cottage cheese, ½ cup 480 mg sodium

Cornflakes, 1½ cups 400 mg sodium

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To start hydrating, 4 hours before:

Use sport drinks, water or juices of choice

Drink 2-3 ml per pound body weight Example: 150 lb adult = 10 – 15 oz 

If no excess fluid is eliminated within 2 hours, then continue to drink more fluids. Aim for another 5 - 10 oz over the next hour.  

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To ensure optimal hydration, in addition to above, 2 hours before drink fluids with a higher sodium content:

Example:  5-oz tomato juice or V-8 juice = 480 mg sodium

       1/2 cup chicken broth = 480 mg sodium

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Photo by Hannah Coleman on Unsplash

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About the Author

Donna Marlor, MA, RD, CSSD

Donna Marlor is a registered dietitian (RD) specializing in nutrition for endurance exercise and weight management. She offers motivational coaching and behavioral skills training to change eating patterns. Donna has a successful private practice as a consultant to the U.S. Olympic Education Center in Marquette, MI, and works with many individual athletes from novice to elite. A former collegiate alpine and cross country racer, Donna has a personal interest in sports.

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