Electrolytes explained: sodium, cramp and what actually helps

Electrolyte marketing has turned a fairly narrow physiological question into a shelf full of products. The underlying facts are simpler: you lose sodium in sweat, the amount varies enormously between riders, and the link between that loss and the cramp you got at kilometre 140 is far weaker than the industry suggests.

This piece separates the three things that get conflated — what electrolytes do, why cyclists cramp, and what is actually worth drinking.

What electrolytes actually do

Electrolytes are minerals that carry an electrical charge in body fluid — principally sodium, plus chloride, potassium, calcium and magnesium. They govern how fluid is distributed between your blood and your cells, and they're central to how nerve signals travel and how muscle fibres contract.

Sodium is the one worth thinking about on a bike, for one reason: it is by far the most abundant electrolyte in sweat. Potassium and magnesium losses in a normal ride are small relative to what you carry and what you eat. If a drink's headline feature is its magnesium content, that is a marketing decision, not a physiological one.

How much sodium you actually lose

Here is the number that makes generic advice useless. Whole-body sweat sodium concentration in athletes runs roughly 10 to 70 mmol per litre, with local measurements spanning about 10 to 90 — a sevenfold to ninefold spread between individuals. Two riders side by side in the same conditions can lose wildly different amounts of salt.

Notice the range: somewhere between roughly 200 mg and 2,200 mg of sodium an hour depending on who you are and how hard the day is. That's why a fixed recommendation — "one tablet per bottle" — is meaningless. It is either too much or too little for almost everybody.

The cramp question

Exercise-associated muscle cramp is the reason most riders buy electrolytes in the first place. It is also the claim with the weakest evidence behind it. Two competing explanations have been argued over for decades, and they make different predictions.

The current weight of evidence leans towards the neuromuscular explanation. Reviews of the field conclude that dehydration and electrolyte depletion, on their own, do not explain most cases of cramp — and the strongest predictors are a prior history of cramping and riding harder or longer than you're trained for. That is an uncomfortable message, because it means the fix is mostly training and pacing, which nobody can sell you in a sachet.

Some honesty is required here, though: this is not settled. A subset of riders with very high sweat sodium losses do seem to respond to sodium, and the literature is mostly observational. If salt tablets have reliably worked for you over years, the evidence isn't strong enough to tell you you're wrong. It is strong enough to say they won't work for most people.

The risk that goes the other way

Over-drinking is the failure mode that actually hospitalises people. Exercise-associated hyponatraemia — blood sodium below 135 mmol/L — is caused predominantly by drinking more fluid than you lose, which dilutes the sodium in your blood. Mild cases feel like bloating, nausea and a headache; severe cases cause confusion, seizures and, rarely, death.

The international consensus on this is blunt: the primary prevention is not drinking to a schedule. Riders who force fluid down because a plan says 750 ml an hour, regardless of heat or effort, are taking the one risk in this article that can genuinely end a day in hospital. Drinking to thirst is, for the overwhelming majority of amateur riders, both safe and sufficient.

So what should you actually drink?

If you want your own number rather than a range, the crude home method still works: weigh yourself naked before and after a hard hour, add back the weight of anything you drank, and the difference is roughly your sweat rate. It won't tell you your sweat sodium — that needs a proper test — but it tells you whether you're a 0.5 L/h rider or a 1.8 L/h rider, which is most of what matters. Our cycling hydration strategy guide has the full protocol.

The unglamorous conclusion

• Sodium is the electrolyte that matters on a bike. The rest are largely along for the ride.
• Your losses are individual to a degree that makes generic dosing advice worthless.
• Electrolytes are unlikely to cure your cramp. Fatigue and pacing beyond your preparation are the better-supported culprits.
• Carbohydrate does more for long-ride performance than any electrolyte formulation — see fuelling long rides.
• Don't over-drink. It is the only mistake here with a serious downside.

If cramp keeps ending your long rides at the same point, the most productive thing you can change is usually the preparation rather than the bottle: more time at the duration and intensity the event actually demands. That's a training problem, and building towards it gradually — which is what Moveee's adaptive plans do as your real rides come in — will do more than any sachet.