Electrolytes: The Hydration Detail Everyone Skips

You track your protein, you plan your training week, you have opinions about sleep. The one thing nobody plans: what leaves your body with every drop of sweat. Because water alone is only half the hydration story. Get this detail right and long sessions feel different; get it wrong and you'll hit walls you end up blaming on everything else.

What electrolytes are – and why sodium runs the show

Electrolytes are charged minerals: sodium, potassium, chloride, magnesium and calcium. They're the signaling system of your body. Muscle cells and nerves only fire because these ions build up and pass on electrical charge – and they're what pulls water to where it's needed. Without them, the whole concept of hydration stays theory.

Sweat is, for the most part, water and salt. And not all electrolytes are lost in equal amounts. Sports science is unusually clear here: sodium is the mineral you lose in the largest quantity in sweat – and the one with the biggest impact on your fluid balance. Reviews in Sports Medicine and Current Sports Medicine Reports have described this consistently for years. In active people, sweat sodium concentration typically lands between 10 and 70 millimoles per liter, with huge variation between individuals.

That sounds abstract until you do the math: lose two liters of sweat in a session at a middling 40 millimoles of sodium per liter, and you've given away roughly 1,800 milligrams of sodium. More than one and a half grams of salt, gone, in a few hours – and that's the moderate version.

What an hour of training actually costs you

How much you sweat varies wildly. Somewhere between half a liter and two liters per hour is normal territory for trainees. Normative data from the Journal of Sports Sciences, gathered from over 1,300 athletes, shows endurance sports with the highest rates outside American football: around 1.2 to 1.3 liters of sweat per hour, and with it roughly 50 millimoles of sodium per hour. Team and ball sports sit a bit lower, but in the same range.

Two things turn a heavy sweater into someone who should think about this deliberately. First: the more you sweat, the higher the sodium concentration of that sweat tends to get. You lose twice. Second: sweat saltiness is individual and partly genetic. People with salty sweat recognize themselves by the white rings left on their skin after a run. If you see those, you're losing an outsized amount of sodium.

Then there's the actual reason sodium matters so much in sport: it holds water in. Drinks with sodium stay in the body better; water without salt rushes straight through. That's not marketing, it's physiology – and it's the lever your hydration hinges on.

When water is enough – and when it isn't

You can relax about the short stuff. The American College of Sports Medicine says it in its position stand on fluid replacement, year after year: for exercise under an hour in moderate conditions, water is completely sufficient. An electrolyte drink adds nothing plain water doesn't already do. Only for sessions beyond an hour does the ACSM recommend adding sodium to your fluid – roughly 0.5 to 0.7 grams per liter – because it makes the drink more palatable, keeps fluid in the body better and, in certain cases, guards against blood sodium dropping too low.

The German Nutrition Society (DGE) puts numbers on it: an optimal sports drink for longer sessions contains 400 to 1,100 milligrams of sodium per liter plus four to eight percent carbohydrates. And it names the threshold where sodium really starts to matter – that's when your sweat rate exceeds 1.2 liters per hour and the effort runs longer than two hours.

Translated, that means: an hour of strength training, a run around the block, the weekly gym routine – all water territory, as long as you eat normally. Only when the session gets long, the heat arrives or you belong to the heavy sweaters does the game change. And here's the honest side note: those neon sports drink bottles simply aren't necessary for most people's everyday lives. They're sugar first – for normal movement, water is the healthier drink, and systematic reviews agree.

The real danger is the opposite: too much water

Here's the paradox, and it's exactly why this topic earns its place. The classic failure mode in endurance sport isn't too little water – it's too much. It's called exercise-associated hyponatremia (EAH): drink more hypotonic fluid during a long effort than your kidneys can excrete, and you dilute your blood sodium. The concentration falls, and symptoms range from bloating and headache to genuinely serious courses. The consensus documents in sports medicine – including the third international EAH consensus statement – are unambiguous and recommend drinking to thirst, especially in long events. Chugging fixed volumes on a schedule, thirsty or not, is yesterday's advice.

The practical consequence: at a long race or a hot tournament, don't drink on a program – follow your thirst. And if you sweat a lot, make sure the drink carries sodium. Plain water through hours of heavy sweating is exactly the combination that drags blood sodium down.

Cramps: the honest section

Here comes the part that's supposed to save everyone's day – or isn't. The popular equation "cramp equals electrolyte deficiency" doesn't survive contact with the data. Sports physician Martin Schwellnus worked this topic for years and dismantled the once-dominant electrolyte doctrine: exercise-associated muscle cramps are multifactorial, and the best evidence points at fatigued muscles and disrupted coordination between nerves and muscles – not salt in your sweat. Studies on runners and even on Ironman triathletes found no consistent electrolyte differences between athletes with and without cramps. Stronger predictors included a history of cramps and your pace.

To be fair, there's the historical counter-evidence: in the classic heat-worker studies of the 1920s and 30s – miners, steelworkers, ships' stokers – salty drinks massively reduced cramp rates. But that's a different context: extreme heat, extreme sweat losses, stretched over days. In normal training, don't read every cramp as an electrolyte emergency. Check load, sleep and hydration first – then the minerals.

Your electrolyte game plan

Everyday life is simple: if you eat normally, your meals cover your sodium needs. Research finds no evidence that athletes need an extra daily salt ration – a 2025 review on sodium intake for athletes states exactly that, soberly. Normal food reliably covers the baseline.

The interesting part happens around long sessions. During: for more than 60 to 90 minutes of sweating, or in heat, choose a drink with sodium. After: replace fluid and salt together, so the water actually sticks. An isotonic drink with electrolytes and magnesium – FitLine's Restorate – refills fluid and minerals after a sweaty session and is noticeably easier on the stomach than the fifth sugary sports bottle.

And a self-test that tells you in five seconds where you stand: white rings on your skin after training? Then you're a salty sweater, and you should pay extra attention to sodium on long sessions. No rings, short sessions, mild weather? Then water is your best friend – and you can tick this topic off for now.

Electrolytes aren't hype. They're the detail that turns plain water into actual hydration – exactly when the session demands it. Long, hot, sweaty: add sodium. Short and easy: water's fine. And if a cramp shows up anyway: check load, sleep and pace before you reach for the salt shaker.