Electrolytes: What They Actually Do, Dosage, and Whether They're Worth It

In a few short years electrolytes went from something handed out at marathon aid stations to a product marketed at anyone who breaks a sweat. The truth is duller: they are ordinary mineral salts your body loses in sweat, and in most cases food and water replace them fine. But there are specific situations where a supplement genuinely changes how a session feels, and it is worth knowing exactly which ones.

What electrolytes do, and what they don't

Electrolytes are minerals that carry an electrical charge in water, which is how nerves fire signals and muscles contract. Four matter for training:

• Sodium — the main electrolyte outside your cells. It holds blood volume and retains fluid, and it is by far the one you lose most in sweat.
• Potassium — works inside the cells, involved in muscle contraction and heart rhythm.
• Magnesium — a cofactor in over 300 enzyme reactions, including ATP production and muscle relaxation after a contraction.
• Chloride and calcium — chloride travels with sodium, and calcium is what physically triggers the fibre to contract.

What electrolytes do not do: they contain zero calories so they give no energy, they don't build muscle, they don't speed up metabolism, and they don't detox anything. If you're flat because you sleep 5 hours and eat 1,400 calories, powder in water won't fix it.

How much you actually lose

An average person loses 0.5 to 1.5 litres of sweat per hour in training, and over 2 litres in heat or on long runs. Sodium concentration varies enormously — roughly 200 to 2,000 mg per litre, averaging around 900 mg/L. Potassium runs about 200 mg per litre, and magnesium only 5 to 10 mg per litre, which is trivial next to the 300–400 mg you already eat daily.

Measure instead of guessing. Weigh yourself naked before training and again straight after, towelled dry. Every kilogram lost is roughly a litre of fluid. Example: 78.0 kg before, 77.2 kg after, and you drank 500 ml during — that's about 1.3 litres of sweat. Repeat it 2–3 times in different conditions and you have your real number.

When it makes no sense

If you train 45–75 minutes in an air-conditioned gym, eat normally and drink to thirst, you don't need electrolytes. A typical diet already delivers 3,000–4,500 mg of sodium a day, which is above every guideline out there. Buying a drink mix for a one-hour lifting session is money thrown away.

When it does make sense

• Training or running longer than 90 minutes, or longer than 60 minutes above 27 °C.
• A sweat rate over 1.2 litres per hour, or white salt marks on your shirt once it dries.
• Two sessions in one day with less than 6 hours between them.
• The first 1–2 weeks of a low-carb diet, when the kidneys dump extra sodium.
• After diarrhoea, vomiting, or a long sauna session.
• A restrictive diet under 1,600 calories where you cut out nearly all processed food — and the salt with it.

Doses: the actual numbers

• Sodium: 300–600 mg per litre of fluid for efforts of 1 to 2 hours; 600–1,000 mg per litre beyond 2 hours or if you're a salty sweater. DIY version: 1 litre of water + 1.5 g of table salt (about a quarter teaspoon) gives roughly 600 mg of sodium. For efforts over 90 minutes, add 30–60 g of carbohydrate per litre.
• Potassium: 150–300 mg per litre is plenty, and it's easier to eat — one banana has about 420 mg, 200 g of boiled potato about 800 mg.
• Magnesium: 200–400 mg of elemental magnesium daily, ideally in the evening. Citrate, glycinate and malate absorb far better than oxide. Above 400 mg from a supplement usually means diarrhoea. Daily requirement is 310–320 mg for women and 400–420 mg for men, and most of it should come from food.
• Rehydrating afterwards: drink 125–150 % of the weight you lost over the next 2–4 hours. Down 1 kg, drink 1.25–1.5 litres — and include sodium, or plain water mostly goes straight to urine.

If a drink mix hasn't made a visible difference over 2–3 weeks of the same training, it isn't making one at all.

Cramps: the unpopular truth

Cramps get blamed on electrolytes, but studies comparing people who cramp with people who don't mostly find no difference in mineral levels. The stronger link is neuromuscular fatigue: a jump in load, a new exercise, too many sets taken to failure. Before buying powder, check whether you've added more than 20 % to your total volume in the last 2 weeks, whether you sleep 7–9 hours, and whether you're eating 4–6 g of carbohydrate per kilogram on hard days. If cramps still show up in the final third of long sessions, trial 500–1,000 mg of sodium per litre for 3 weeks and judge from there.

More is not better

Drinking too much plain water — over 1 to 1.5 litres per hour for several hours — can dilute blood sodium below 135 mmol/L. That's hyponatraemia, and it's serious. Signs are headache, nausea, bloating, puffy fingers, confusion, and the clearest signal of all, gaining weight during the session. Equally, if you have high blood pressure, an extra 5 g of salt a day is not neutral.

When to see a doctor

• You take diuretics, ACE inhibitors or blood pressure medication — don't add sodium or potassium without asking first.
• You have kidney disease, heart disease, or a known arrhythmia.
• Cramps last longer than 4 weeks, hit at rest or at night, or come with tingling and weakness.
• Confusion, severe headache or vomiting after a long effort — that's an emergency.
• Diarrhoea or vomiting lasting more than 48 hours, especially with dizziness on standing.
• Palpitations or fainting during training, no matter how good you otherwise feel.

The short version

• Electrolytes replace what you lose in sweat — they give no energy and build no muscle.
• For gym sessions under 75 minutes, water is entirely enough.
• Weigh in before and after: 1 kg of difference is about 1 litre of sweat, and that number decides whether you need anything at all.
• The working dose is 300–1,000 mg of sodium per litre, and 1.5 g of ordinary salt in a litre of water gives about 600 mg.
• Magnesium 200–400 mg daily as citrate or glycinate; oxide mostly ends up in the toilet.