Have you ever touched your face after a run and felt a gritty texture? Or looked down at your arms to find them dusted with white streaks? Those are salt crystals, clear signs that your body has been working hard to keep you cool.
When we run, our core temperature rises, and sweating becomes our primary cooling mechanism.
But while sweat helps prevent overheating, it also means we’re losing not just fluid, but essential electrolytes like sodium, potassium, magnesium, and chloride, minerals that play critical roles in muscle function, nerve signaling, blood pressure regulation, and overall performance.
For runners, staying hydrated isn’t just about avoiding thirst. It’s about maintaining the delicate balance of fluids and electrolytes that keeps our muscles firing properly, prevents cramping, supports endurance, and helps us recover faster.
Even mild dehydration or electrolyte imbalance can impair performance, elevate perceived exertion, and increase the risk of heat-related issues.
That’s why replenishing both fluids and electrolytes during longer runs, intense training sessions, or hot-weather workouts is key to running strong and feeling your best.
In this guide, we’ll break down everything you need to know to hydrate smarter and maintain optimal electrolyte balance—before, during, and after your runs.
What Are Electrolytes?
According to the National Library of Medicine,1National Library of Medicine – National Institutes of Health. (n.d.). Www.nlm.nih.gov. Retrieved June 3, 2024, from https://www.nlm.nih.gov/?_ga=2.248344513.798999400.1643050854-625113316.1641830008 electrolytes are “minerals in your body that have an electric charge. They are in your blood, urine, tissues, and other body fluids.”
The electrolytes found in our body are sodium, potassium, magnesium, chloride, phosphate, and calcium. We will discuss the most important ones for runners (in no particular order).
#1: Sodium
Sodium helps regulate proper fluid and electrolyte mineral balance so you don’t get dehydrated. It also assists with muscle contractions and nerve function.
#2: Potassium
Potassium is used in various vital bodily functions, such as regulating fluid and electrolyte balance, nerve signals, and muscle contractions. It also promotes glycogen storage and aids in the transportation of nutrients.
For runners, if we don’t have enough potassium, our muscles can’t contract properly, leading to cramping.
#3: Magnesium
Magnesium is used for energy production, metabolism, muscle and nerve contractions, muscle recovery, and general bone health.
It also helps avoid cramping.
Why Is Electrolyte Balance Important For Runners?
There is a common misconception that runners can stay sufficiently hydrated only with water.
Hydration isn’t just about replenishing fluid but also minerals. When we sweat, we expel not only water but heaps of crucial mineral electrolytes, too. That’s the grainy feeling on your skin that I mentioned before.
Specifically for runners’ needs, replenishing these electrolytes helps us avoid muscle cramping and fatigue, regulates our heartbeat, and keeps our body well-hydrated. As you can imagine, it also aids in performance.
If our body is functioning efficiently on a general-health daily basis, it will perform at its best while exercising as well. This is the goal.
Even a 2% decrease in body weight during exercise can result in impaired performance.2Latzka, W. A., & Montain, S. J. (1999). WATER AND ELECTROLYTE REQUIREMENTS FOR EXERCISE. Clinics in Sports Medicine, 18(3), 513–524. https://doi.org/10.1016/s0278-5919(05)70165-4
What Are The Consequences of Fluid and Electrolyte Depletion?
If you don’t consume enough electrolytes along with your fluid intake, you could not only experience the familiar runner repercussions such as cramping and stitches but any number of issues that can affect your health. These include:
- The body’s inability to regulate body temperature
- Confusion and poor decision making
- Dizziness
- Nausea
- Irregular heartbeat
- Fluid retention
- Dry mouth
- Gastrointestinal issues
These are some of the most common effects of dehydration, but we should also mention overhydration which is overhydrating without supplementing with the proper amount of electrolytes.
This overhydration results in a condition called hyponatremia, which can be very dangerous.
Hyponatremia
Hyponatremia is a condition caused by overhydration, in which the sodium concentration in the blood becomes dangerously diluted.3Clinical Journal of the American Society of Nephrology. (n.d.). Journals.lww.com. https://journals.lww.com/cjasn/Pages/default.aspx Without enough sodium, the body cannot properly regulate the amount of water inside and around its cells, leading to cellular swelling.
This condition has been documented in marathoners, especially during unexpectedly warm races, when runners, attempting to stay ahead of dehydration, drink excessive amounts of water.
Common symptoms of hyponatremia include nausea, vomiting, headache, confusion, fatigue, and muscle cramps. Because these overlap with dehydration symptoms, the condition can be challenging to recognize. In severe cases, hyponatremia can lead to seizures, loss of consciousness, or even coma.
I mention this because hydration isn’t just about drinking more; it’s about drinking smart.
Runners can avoid hyponatremia by balancing water intake with electrolytes, especially sodium. This ensures proper hydration without diluting the essential minerals your body needs to function well.
How Much Fluid Should Runners Drink During A Run To Stay Hydrated?
There is some new technology that actively measures your sweat and electrolyte loss in real time, such as the Nix Hydration Biosensor.
This wearable patch analyzes the composition of your sweat during exercise. It sends live updates to an app, giving you personalized alerts about when to drink and how much electrolyte replacement you need.
For endurance athletes, this is a powerful tool. Sweat rates and sodium losses vary dramatically from person to person. Some runners lose only a small amount of salt, while others are “salty sweaters” who shed large amounts of sodium per hour.
Understanding your individual sweat profile helps you replace the right amount of fluids and electrolytes, preventing both dehydration and overhydration while optimizing performance.
Of course, not everyone has access to this type of technology, which is why a simple DIY sweat test can still be incredibly valuable. By measuring your body weight before and after a run (and accounting for any fluids consumed), you can estimate how much fluid you lose per hour.
This gives you a ballpark figure for your sweat rate and helps you build a smarter, more personalized hydration plan to support your training and racing.
The Sweat Test: How To Calculate Fluid Loss
1. Weigh yourself with no clothes or shoes on.
2. Run for one hour at your race pace or training pace, ideally in the conditions in which you will race or often train. You want this data to be accurate for your daily training and/or race.
Note: During your run, do not consume or expel any liquid…so in simpler terms: no drinking or peeing! This will throw off your calculation. If you must drink water because of the weather conditions, you must take that into consideration when calculating your sweat rate, adding this fluid to the equation.
3. After your one-hour run, take off your shoes, clothes, and if necessary, wring out your sopping wet hair.
4. Weigh yourself again.
Now calculate your results.
Take your pre-run weight and subtract your post-run weight. This weight loss will be your sweat loss per hour while you run. Let’s take a look at examples using kilos and pounds:
Kilos:
50 kilos (pre-run weight) – 48.5 kilos (post-run weight) = 1.5 kilos = 1.5 liters per hour
Pounds:
125 pounds (pre-run weight) – 122 pounds (post-run weight) = 3 pounds = 48 ounces per hour
The goal is to get as close as possible to replenishing your fluid loss while you run; however, 80% is a more reasonable goal if you are a heavy sweater.
Measuring Electrolyte Loss
If you can’t perform a lab-based sweat test or use tech that calculates your electrolyte needs in real time, trial and error is a perfectly valid and effective approach. Like most aspects of endurance training, practice makes perfect.
Use your training runs as opportunities to hone your hydration and electrolyte strategy. Pay attention to how you feel in different temperatures, how often you crave fluids, whether you experience cramping, and how your energy levels and recovery respond.
Over time, these patterns help you dial in the right combination for race day or peak training periods.
There are many electrolyte-replenishment options to experiment with, including:
- Electrolyte tablets (e.g., Nuun)
- Salt chews (e.g., SaltStick FastChews)
- Electrolyte capsules
- Electrolyte powders you mix into a bottle
- Electrolyte beverages and sports drinks (e.g., Gatorade, Skratch, Tailwind)
- Energy gels, many of which also contain sodium and other key minerals
You can also track practical markers during your runs, such as:
- Feeling bloated or waterlogged (a sign you may be taking in too much fluid relative to sodium)
- Salt residue on your skin or clothing (a sign you may need more sodium)
- Cramping
- Unusually high thirst
In addition, you can use this general recommendation as a guideline for running in the heat which is to consume 300-600 milligrams of sodium per hour during prolonged exercise.4University, U. S. (n.d.). Maintaining Hydration: A Guide for Endurance Runners. Extension.usu.edu. Retrieved June 3, 2024, from https://extension.usu.edu/nutrition/research/maintaining-hydration-a-guide-for-endurance-runners#:~:text=As%20a%20good%20rule%20of
However, this number can vary greatly depending on the individual’s sweat rate and running conditions. If you are a salty sweater, you may need additional sodium intake compared to a person who is not.
You’ll know you have found your balance when you do not experience cramping or other dehydration symptoms during a race, run, or intense exercise session. You’ll likely also see improvements in your performance and recovery.
To start, use sources of fluid and electrolytes such as sports hydration drinks during your next run for over an hour. This will help significantly replenish the electrolytes you are expelling when you sweat.
You can choose drinks with or without carbohydrates, depending on your needs.
Sports drinks that contain carbohydrates help to increase water absorption into the bloodstream. You also won’t have to consume as many products, such as gels or gummies, because your sugar will come straight from your hydration.
If you try this out and are still cramping or feeling signs of dehydration, you may need to include additional sources of electrolytes, such as salt pills, into your regimen.
Most sports salt pill supplements contain sodium, potassium, calcium, and magnesium – precisely what we need to get back into our system.
Another option is to make your own DIY electrolyte drink by mixing your favorite fruits and veggies that are high in electrolytes. Take a peek at this recipe.
Other Factors That Affect Fluid and Electrolyte Levels
There will be other factors that will affect the amount of fluid and electrolytes you will need, such as:
- Weather:5Oliveira, R. A., Sierra, A. P. R., Benetti, M., Ghorayeb, N., Sierra, C. A., Kiss, M. A. P. D. M., & Cury-Boaventura, M. F. (2017, December 21). Impact of Hot Environment on Fluid and Electrolyte Imbalance, Renal Damage, Hemolysis, and Immune Activation Postmarathon. Oxidative Medicine and Cellular Longevity. https://www.hindawi.com/journals/omcl/2017/9824192/ The hotter and more humid conditions you run in, the more you will sweat and, in turn, need to replenish with sources of electrolytes.
- Duration: The longer the run, the more you will need to replenish.
- If your run is 30 minutes, you can get away with drinking before and after and not during.
- If you are running between 30- 60 minutes, water should be just fine.
- If your run is over 60 minutes, it is a good idea to bring a sports drink or DIY electrolyte drink along to replenish during your workout.
- Intensity: The higher the intensity, the more you will sweat, and the more you will need to replenish your fluid and electrolytes.
5 Tips For A Good fluid And electrolyte balance
#1: Hydrate Regularly
Don’t just think about hydration when you’re working out, but as a constant, day-to-day priority. Most adults can rely on roughly 2 liters (about 67 ounces) of water per day as a baseline for proper hydration, but athletes typically need more.
Many sports nutritionists recommend that runners consume 30–35 mL of fluid per kilogram of body weight per day (about 0.45–0.53 ounces of fluid per pound of body weight per day)—roughly 2–3 liters (68–101 ounces) for most athletes—plus additional water to replace sweat losses, especially when training in heat, humidity, or at altitude.
Many sports nutritionists recommend that runners consume 30–35 mL of fluid per kilogram of body weight per day (roughly 2–3 liters (68–101 ounces) for most athletes), plus additional water to replace sweat losses, especially when training in heat, humidity, or at altitude.6Sawka, M., Burke, L., Eichner, E., Maughan, R., Montain, S., & Stachenfeld, N. (2007, February 1). American College of Sports Medicine Position Stand. Exercise and Fluid Replacement. Medicine and Science in Sports and Exercise. https://pubmed.ncbi.nlm.nih.gov/17277604/
A simple strategy is always to carry a water bottle and sip consistently throughout the day rather than chugging large amounts at once. Aim for pale-yellow urine as a general indicator of hydration, and increase your intake on days when you’re training hard, spending time outdoors, or feeling dehydrated.
#2: Hydrate Before You Run
Aim to drink about 500 mL (17 ounces) of fluid with your pre-run snack roughly two hours before your run. This gives your body time to absorb the liquid, optimize blood plasma volume, and allow any excess to pass so you won’t feel sloshy when you start running.
Choosing something like juice can give you an extra boost of carbohydrates, fueling your muscles while also topping off hydration, effectively killing two birds with one stone.
If you tend to wake up dehydrated or are heading into a hot or long session, you can also sip another 200–300 mL (7–10 ounces) about 15–20 minutes before heading out.
#3: Hydrate During Your Runs
If your run lasts longer than 60 minutes, make sure to replace about 80% of your average fluid loss during the workout, based on your sweat test results.
Remember to hydrate with electrolytes, not just water. Sodium is particularly important for maintaining fluid balance, preventing cramps, and improving absorption.
Depending on your sweat rate and sweat sodium concentration, this may mean using sports drinks, electrolyte powders, salt capsules, or gels that contain electrolytes.
Your goal is to stay ahead of dehydration without overhydrating—balancing fluids and electrolytes is what keeps your body performing at its best.
#4: Replenish Your Fluid and Electrolytes After Your Runs
Just because you hydrated before and during your run doesn’t mean you’re done. Post-run rehydration is just as essential.
After you finish, replenish with a recovery drink that includes the key electrolytes you’ve lost, especially sodium and potassium.
A well-rounded recovery option should also provide protein (to repair muscle tissue) and carbohydrates (to restore glycogen levels), giving your body everything it needs to bounce back strong.
#5: Eat a Well-Balanced Diet
Eating a well-balanced diet, including water- and electrolyte-rich foods, can help replenish fluids and essential minerals lost during running. Here are some great options to support daily hydration and recovery:
- Fruit: Watermelon, strawberries, cantaloupe, peaches, oranges, bananas (potassium-rich), pineapple, kiwi, and tomatoes
- Vegetables: Cucumber, lettuce, spinach, kale, celery, zucchini, cauliflower, broccoli, bell peppers, and sweet potatoes (excellent potassium source)
- Other Hydrating Options: Soup and broth (especially helpful for sodium), skim milk or chocolate milk (contains sodium, potassium, and fluids), coconut water (natural electrolytes), yogurt, kefir, and electrolyte-enhanced waters
These foods not only help you stay hydrated but also provide key minerals like sodium, potassium, magnesium, and calcium that support muscle function, nerve signaling, and proper hydration balance.
From our daily hydration to our running-specific strategies, we need to attend to these details for the sake of our performance and, more importantly, our health.
For even more information on hydration, check out the following guide:
Hello,
Thanks for the great article and content in general.
I just have one note I noticed:
50 kilos (pre-run weight) – 49.5 kilos (post-run weight) = 1.5 kilos
where 1.5 should in fact be 0.5 because 50 – 49.5 = 0.5.
Have a great day and keep running!
BR,
Martin
Thanks Martin!!! Adjusted so the post-run weight is 48.5kg, now the maths flow 🙂
Thomas from Marathon Handbook