When you run or train, you lose fluid and electrolytes - mainly sodium - through sweat. Replacing them helps you stay hydrated and supports normal muscle function on longer or hotter sessions. Sodium is the main electrolyte to focus on, with potassium and magnesium alongside. For most everyday runs, water and a balanced diet are enough; electrolytes earn their place as sessions get longer, hotter and sweatier.
Why runners lose electrolytes
Sweat is mostly water, but it also carries electrolytes - and sodium most of all. The longer and harder you run, and the hotter the conditions, the more you sweat and the more sodium you lose. Replacing fluid alone with plain water does not put back that sodium. That is the gap an electrolyte drink fills: it helps you replace both the fluid and the minerals you have sweated out, which supports hydration and normal muscle function.
How much do you actually lose? The numbers
Sweat losses vary enormously between people, but sports-science research gives useful ballpark figures:
|
What |
Typical range |
Source
|
|---|---|---|
|
Sweat rate during exercise |
About 0.5 to 2.0 litres per hour (rarely above 3.0 L/h) |
|
|
Sodium in sweat |
About 230 to 2,070 mg per litre (roughly 10 to 90 mmol/L), averaging around 1,150 mg/L |
|
|
Sodium lost per hour (endurance) |
Around 1.2 g per hour on average, with a very wide spread |
To make that concrete: a researcher's worked example had one athlete lose about 2.2 g of sodium over a 1 hour 45 minute session (GSSI). These are population averages with a big individual range, so treat them as illustrative, not a prescription - your own losses depend on your body, the intensity and the weather.
Sweat rates vary a lot - and so does the salt
There is no one-size-fits-all number, because sweat rate and sweat sodium both vary hugely between people. A few things shift them:
-
Heat and humidity raise your sweat rate.
-
Heat acclimatisation does the opposite for salt - as you adapt to training in the heat, your body conserves sodium and your sweat gets less salty (Baker 2017).
-
Your diet matters too: over a week or two, a higher-salt diet raises sweat sodium and a lower-salt diet lowers it (Baker 2017).
-
You may simply be a "salty sweater." If you finish a run with white salt marks or a gritty residue on your skin, cap or a dark shirt, you are likely on the higher-sodium end and may benefit more from replacing it. It is a rough self-check, not a lab test.
The electrolytes that matter for runners
-
Sodium. The priority. It is the main electrolyte lost in sweat and the one most linked to hydration on long efforts.
-
Potassium. Works with sodium in fluid balance and supports normal muscle function.
-
Magnesium. Involved in normal muscle function and energy metabolism.
A balanced electrolyte powder or tablet usually covers all three.
Before, during and after a run
-
Before. Start well hydrated. For an early-morning or hot session, an electrolyte drink beforehand tops up your fluid and sodium.
-
During. Mainstream guidance is to include sodium in your fluids for exercise lasting longer than about two hours, or any session that causes heavy sodium loss - and that threshold comes forward in the heat (ACSM position stand). For long endurance efforts, a version with some carbohydrate can also provide fuel.
-
After. Rehydrate with fluid and electrolytes to support recovery of your hydration after a sweaty session.
For short, easy runs in mild weather, water is usually fine - you do not need an electrolyte drink for every jog.
Important: do not over-drink
More water is not always better. Drinking far more fluid than you lose during long events - well past thirst - can dilute the sodium in your blood, a condition called exercise-associated hyponatremia (EAH). It is a real risk in marathons, ultramarathons and triathlons, especially events over two hours, and in its serious form it can be dangerous (Hew-Butler et al., Frontiers in Medicine, 2017). The safest approach the research points to is simple: drink to thirst rather than forcing large volumes, and include sodium on long, hot or sweaty sessions rather than relying on plain water alone.
Sugar-free or with carbs?
For short and moderate runs where you just want hydration, a sugar-free electrolyte does the job. For long endurance sessions where you also need energy, a version with carbohydrates provides fuel as well as electrolytes. Match the product to the session.
What about cramps?
Muscle cramp is complex and not fully understood, and it is not as simple as "low electrolytes = cramps." Electrolytes, particularly sodium and magnesium, play a role in normal muscle function, and staying hydrated and topped up is sensible for runners - but an electrolyte drink is not a guaranteed cramp fix. If you get frequent or severe cramps, it is worth speaking to a sports doctor or physio.
How to choose
Look at the sodium level (higher for long, hot, sweaty sessions; lighter for everyday), whether you want sugar-free or carbohydrate (hydration vs fuel), and the format - a powder you mix in a bottle, or tablets you drop in on the go.
This is a supplementary product and is not intended to diagnose, treat, cure, or prevent any disease.
Frequently Asked Questions
Do runners need electrolytes?
For short, easy runs in mild weather, water and a balanced diet are usually enough. Electrolytes become useful as runs get longer, hotter and sweatier - mainstream guidance points to sessions beyond about two hours, or sooner in heat - because you lose fluid and sodium through sweat that plain water does not replace.
How much sodium do runners lose in sweat?
It varies a lot, but sweat contains roughly 230 to 2,070 mg of sodium per litre (averaging around 1,150 mg/L), and endurance athletes lose on the order of 1 g or more per hour (Baker 2017; GSSI). Your own losses depend on your sweat rate, the heat and your physiology, so treat these as ballpark figures.
What electrolytes are best for running?
Sodium is the priority, since it is the main electrolyte lost in sweat, with potassium and magnesium alongside. A balanced electrolyte powder or tablet usually covers all three. For long endurance sessions, a version with carbohydrate also provides fuel.
Should I take electrolytes before, during or after running?
All three can help depending on the session. Start well hydrated, include sodium during runs beyond about two hours or in heat, and rehydrate with fluid and electrolytes afterwards. For short, easy runs, water is usually enough.
Can you drink too much during a run?
Yes. Drinking far more than you lose, well past thirst, can dilute your blood sodium (exercise-associated hyponatremia), which is a real risk on long endurance events and can be serious. Drink to thirst, and include sodium on long or hot sessions rather than relying on large volumes of plain water.
Do electrolytes stop cramps?
Not reliably. Electrolytes like sodium and magnesium play a role in normal muscle function, and staying hydrated and topped up is sensible, but cramp is complex and an electrolyte drink is not a guaranteed fix. See a sports doctor or physio for frequent or severe cramps.
Sugar-free or carb electrolytes for runners?
Sugar-free suits shorter and moderate runs where you just want hydration. A carbohydrate version suits long endurance sessions where you also need fuel.
