Independent supplement ratingsUS and Canada · Updated weekly
A ratings desk for a category that has spent thirty years grading its own homework.
A ratings desk for a category that has spent thirty years grading its own homework.
Two numbers decide it, and one of them is close to unpredictable. The best model built on 1,944 sweat tests explains under a quarter of the difference between people.
The short answer: a hard, sweaty hour costs most people somewhere between 400 and 1,600 mg of sodium, and heavy salt sweaters can lose well over 2,000. The range is that wide because one of the two numbers involved is close to unpredictable — the best model anyone has built explains under a quarter of why you differ from the person next to you.
Sodium loss is two numbers multiplied together:
sweat rate (litres per hour) × sodium concentration (mg per litre) = sodium lost.
Sweat rate for an adult training hard runs roughly 0.5 to 2.0 litres an hour, depending on intensity, heat, humidity and body size. Sodium concentration in sweat runs roughly 200 to 2,000 mg per litre, and around 800 mg/L is a reasonable working average.
Multiply the low ends and you get 100 mg — a rounding error you would replace at dinner. Multiply the high ends and you get 4,000 mg, which is more sodium than many people eat in a day. Same hour, same gym.
Our electrolyte calculator runs this for your session length and sweat rate.
In 2022, researchers pooled 1,944 sweat tests from 1,304 people and tried to predict sweat sodium concentration from everything you might reasonably expect to matter. (Baker et al., 2022)
What did not predict it, in any model: age group, race or ethnicity, relative humidity, how long the session lasted, hydration status going in, fluid balance during it, and — this one surprises people — how much sodium you eat.
What did, weakly: energy expenditure, season of the year as a proxy for heat acclimatisation, exercise mode, sex, body mass. Warmer months went with lower sweat sodium, which is acclimatisation doing its job.
And the punchline: together, those models accounted for 17% to 23% of the variation. Four fifths of the difference between two people sweating side by side remains unexplained by every obvious variable.
So when a brand tells you what you need, it is describing an average that may not resemble you. Two honest signals beat any calculator: white crusting on a cap or dark clothing after a session, and a persistent salt taste on your skin. Those are your own concentration showing up on the outside.
Most training does not require replacing sodium during the session.
There is a risk on the other side, and it is the one the category never mentions: drinking large volumes of plain water during long efforts dilutes blood sodium. That is hyponatraemia, and it hurts endurance athletes rather than gym-goers, but it is the reason "just drink more water" is not universally good advice.
Once you have a number, the labels stop being marketing and start being arithmetic. The five electrolyte products in our ranking carry between 55 and 1,000 mg of sodium a serving — an eighteen-fold spread inside one category.
A product at 1,000 mg covers a genuinely hard hour on its own. A product at 55 mg does not meaningfully replace sodium at all, whatever else it does well. Neither is wrong; they are answers to different questions, and only one of them is usually the question being asked.
We took the same five products through the other calculation — what a gram of sodium costs you — in the sodium math on electrolyte labels. The cheapest sodium came from the most expensive stick.
Two sessions of weighing will tell you more than any article, this one included. Run the numbers through the calculator, then see which products in the ranking actually reach them.
Educational only, not medical advice. If you have high blood pressure, kidney disease, or take medication affecting fluid balance, sodium intake is a clinical question — ask your doctor before adding it deliberately.