Electrolytes for running explained: how to hydrate properly during trail runs and races
- Atalen
- May 21
- 6 min read
Trail runners talk a lot about electrolytes, but in practice many people still guess their hydration strategy. Some drink far too much plain water and end up bloated or cramping. Others barely drink at all because they are scared of stomach issues or carrying too much weight.
Electrolytes for running explained properly means understanding a few key things: what electrolytes actually do, how much sodium you realistically lose, how heat changes the equation, and how to build a plan you can execute on race day.
For most runners, the goal is not perfection. It is finding a hydration strategy that keeps energy stable, limits gut problems and remains practical when you are tired, climbing and making decisions badly after 7 hours on the trail.
Quick answers
What are electrolytes for running?
Electrolytes are minerals that help regulate fluid balance, muscle contraction and nerve function. Sodium is usually the most important electrolyte during endurance running.
How much sodium do trail runners need per hour?
Most trail runners need roughly 300 to 800 mg sodium per hour. In very hot conditions or for salty sweaters, this can exceed 1000 mg per hour.
Can drinking too much water be dangerous during races?
Yes. Drinking large amounts of plain water without enough sodium can contribute to hyponatraemia, which is a serious condition linked to low blood sodium levels.
Do all runners need electrolyte drinks?
Not always. Short cool runs may require little or no electrolyte intake. Electrolytes for running explained endurance nutrition becomes more important as duration, heat and sweat loss increase.
What is the easiest way to test an electrolyte plan?
Test it during long runs in similar weather and terrain to your race. Track fluid intake, sodium intake, thirst, stomach comfort and post run body weight changes.
Are electrolyte tablets enough for ultra trail races?
Sometimes, but it depends on the rest of your nutrition. Sodium can come from drinks, gels, sports drink mixes, salty foods or capsules combined together.
Table of contents
What electrolytes for running actually means
Electrolytes are minerals that carry an electrical charge in the body. The main ones involved in endurance sports are sodium, potassium, magnesium and calcium.
For trail runners, sodium matters the most because it is lost in significant amounts through sweat and plays a major role in maintaining fluid balance.
When people say they “need electrolytes”, what they often really mean is one of these things:
They are dehydrated.
They have lost a lot of sodium through sweat.
They are drinking too much plain water.
They are underfuelled and blaming hydration.
Or sometimes they are simply tired and overheating.
This is why electrolyte discussions become messy online. A cramp is not automatically caused by sodium loss. Gut issues are not always caused by dehydration. Headaches during races can come from heat, fuelling errors, pacing or lack of sleep as much as hydration itself.
Electrolytes help, but they are only one part of the system.
Why sodium matters more than most other electrolytes during running
Sweat contains electrolytes, but sodium losses are usually far higher than the others.
Research shows sodium concentration in sweat varies massively between individuals, often ranging from around 200 mg to more than 2000 mg per litre of sweat. Genetics, heat adaptation and diet can all influence this.
That means 2 runners doing the same race in the same weather may have completely different sodium requirements.
A practical example:
Runner A
Sweat rate 600 ml/hour
Moderate sodium concentration
Estimated sodium loss around 400 mg/hour
Runner B
Sweat rate 1.2 L/hour
High sodium concentration
Estimated sodium loss around 1400 mg/hour
These runners should not use the same hydration strategy.
This is also why copying elite runners blindly is risky. Their sweat rates, pacing, body size and gut training may be very different from yours.
How much sodium and fluid trail runners usually need per hour
There is no universal number, but sports nutrition guidelines commonly recommend starting with:
Fluid - around 400 to 800 ml per hour
Sodium - around 300 to 800 mg per hour
Carbohydrates - typically 60 to 90 g carbs per hour for longer events
These numbers change depending on:
Temperature
Humidity
Pace
Body size
Sweat rate
Altitude
Technical terrain
Aid station spacing
Pack carrying capacity
Gut tolerance
A cool 2 hour forest run in the UK may need very little electrolyte support.
A 12 hour alpine ultra in 28°C heat is a completely different situation.
One common mistake is trying to replace 100% of sweat losses. This is often unrealistic and unnecessary during races. Small body weight losses are usually acceptable. Overdrinking can become more dangerous than mild dehydration.
How heat, altitude and race duration change electrolyte needs
Heat changes everything.
Sweat rate increases significantly in hot conditions, and runners often drink more aggressively because they panic about dehydration.
The problem is that thirst and hydration behaviour are not always perfectly matched. Some runners end up consuming litres of plain water while barely increasing sodium intake.
Long races also increase taste fatigue. Sweet drinks and gels can become disgusting after 8 hours. This often reduces total sodium intake accidentally because many runners rely heavily on drink mixes for electrolytes.
Altitude can also increase fluid losses indirectly through increased breathing and dry air exposure.
Practical adjustments that often help in hot races:
Increase sodium gradually before massively increasing fluid
Use multiple sodium sources instead of relying on one product
Keep some salty solid foods later in ultras
Separate carbs and sodium if concentrated drink mixes upset your stomach
Test higher sodium intake during training, not on race day
Common mistakes in electrolytes for running explained nutrition
Drinking only plain water
This becomes riskier during long hot races, especially for slower runners spending many hours on course.
Copying someone else’s hydration plan
Your sweat rate may differ massively from theirs.
Using extremely concentrated drink mixes
Very strong carb and sodium solutions can slow gastric emptying and increase stomach discomfort in some runners.
Ignoring sodium because “I eat enough salt normally”
Daily diet and race hydration are not the same thing.
Waiting until symptoms appear
Once nausea, dizziness or bloating appear, fixing hydration becomes harder.
Assuming every cramp is caused by electrolytes
Cramping is multifactorial. Fatigue, pacing, muscle damage and training load also matter.
How to test an electrolyte strategy before race day
This part matters far more than buying fancy products.
A simple field test can already teach you a lot.
Weigh yourself before and after a long run without changing clothes.
Track:
Fluid intake
Weather
Approximate sodium intake
How thirsty you felt
Gut comfort
Energy stability
Urination frequency
If you lose 1 kg after a 2 hour run despite drinking 1 litre, your sweat losses were probably much higher than expected.
You do not need laboratory precision to improve your strategy. You just need repeatable observations across different conditions.
Many experienced ultra runners gradually build different templates:
Cool weather
Moderate weather
Hot race
High altitude
Very long ultra
That is usually more useful than chasing a single “perfect” hydration formula.
Electrolytes for running explained trail running: practical examples
Example 1 - Cool 3 hour trail run in the UK
Conditions:
12°C
Moderate effort
Frequent refill access
Possible approach:500 ml fluid/hour300 to 400 mg sodium/hour60 g carbs/hour
This may come entirely from sports drink and gels.
Example 2- Hot mountain ultra
Conditions:
28°C
Exposed climbs
Limited aid stations
Possible approach:700 to 1000 ml fluid/hour700 to 1200 mg sodium/hour70 to 90 g carbs/hour.
This may require combining:
Drink mix
Salt capsules
Salty real foods
Water refills
Separate carb sources
Carrying constraints become important here. A runner may technically “need” more fluid than they can realistically carry between aid stations.
This is why practical execution matters as much as physiology.
How to apply this with Atalen
Atalen helps turn hydration theory into something usable during real races.
Instead of only tracking calories or carbs, you can build nutrition plans around actual hourly targets for:
Fluid
Sodium
Carbohydrates
Caffeine
You can compare products and foods by:
Electrolyte content
Serving size
Weight
Taste profile
Ease of use during effort
Practicality in heat or cold conditions
For example, you might realise that one drink mix provides enough sodium but becomes impossible to tolerate after 6 hours, while another combination works better with your gut and aid station strategy.
You can also:
Save hydration templates for different weather conditions
Adapt plans for different race durations
Log what you actually consumed
Track gut comfort and execution after runs
Review patterns over time
Use Strava connected activities alongside nutrition feedback
Over time, this becomes much more useful than relying on memory or guessing during taper week.
Conclusion
Electrolytes for running explained properly is less about finding one magic number and more about understanding your own response to heat, sweat loss and race duration.
Most runners benefit from having a basic sodium and hydration plan instead of improvising completely on race day.
You do not need laboratory testing to improve. A few consistent long run experiments already provide valuable information.
And honestly, the best hydration strategy is often the one you can still execute properly after 9 hours on tired legs while climbing in the heat.
Sources
American College of Sports Medicine Position Stand: https://journals.lww.com/acsm-msse/fulltext/2016/03000/exercise_and_fluid_replacement.22.aspx
International Society of Sports Nutrition Position Stand: https://jissn.biomedcentral.com/articles/10.1186/s12970-019-0289-4
British Dietetic Association Sports Nutrition Factsheet: https://www.bda.uk.com/resource/sport-and-exercise-nutrition.html
Precision Hydration Sweat Testing Resources: https://www.precisionhydration.com/performance-advice/hydration/
Consensus Recommendations on Nutrition for Endurance Athletes: https://bjsm.bmj.com/content/52/7/439
Institute of Medicine Dietary Reference Intakes for Electrolytes: https://www.ncbi.nlm.nih.gov/books/NBK545442/
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