Electrolytes are minerals — mainly sodium, potassium, magnesium, chloride and calcium — that carry an electrical charge when dissolved in water. They keep your muscles firing, your nerves talking and your fluid balance steady. Magnesium, for instance, contributes to normal muscle function and to a reduction of tiredness and fatigue; potassium contributes to normal muscle function and to the normal functioning of the nervous system. Those aren’t marketing lines — they’re EU-authorised health claims, meaning the evidence is solid enough to print on a label. Understanding what electrolytes actually do — and when you genuinely need to top them up — is more useful than reaching for a sports drink every time you finish a jog.
What are electrolytes, and why do athletes lose them?
Every time you sweat, you lose fluid — but you also lose a cocktail of dissolved minerals. Sodium and chloride make up the lion’s share of what leaves your skin; potassium, magnesium and calcium follow in smaller amounts. The exact mix varies enormously from person to person. Some people leave visible white salt rings on their kit after a long session; others barely notice any loss. Genetics, diet, heat acclimatisation and exercise intensity all play a role. That variability matters, because it means there’s no one-size-fits-all answer to “how much do I need to replace?”
Sodium is the electrolyte you lose most of in sweat, which is why it’s the main ingredient in commercial sports drinks. Worth being clear, though: sodium doesn’t have an EU-authorised positive health claim — at a population level most people already eat too much of it. The reason it appears in hydration products is purely functional: during prolonged, heavy sweating, the body does need to replace what it’s lost.
Do you actually need electrolytes — or will water do?
For most workouts, plain water is genuinely fine. If you’re exercising at moderate intensity for under an hour in reasonable weather, your body’s existing electrolyte stores are more than sufficient, and water is all you need. Reaching for an electrolyte drink “just in case” after a 45-minute gym session is unnecessary — and if that drink is a sugary sports beverage, it may add back more than you burned.
Electrolytes become meaningfully relevant in three situations:
- Prolonged exercise — roughly 60–90 minutes or more of sustained effort, where cumulative sweat losses add up.
- Hot or humid conditions — heat drives your sweat rate up significantly, accelerating mineral loss.
- Heavy or salty sweating — if you’re a “salty sweater” (you’ll know from the white kit stains), your sodium losses per litre of sweat are higher than average, and replacement matters more.
None of this requires a specially formulated drink. Many athletes in these scenarios simply eat real food with their water — a banana, a handful of salted nuts, a proper meal — and achieve the same effect. Whole foods bring their own electrolyte package.
The risk of too much plain water
Here’s a nuance that often gets missed: drinking excessive amounts of plain water during very long endurance events can actually be harmful. When you sweat heavily for hours and replace all that fluid with water but no sodium, the concentration of sodium in your blood can fall — a condition called hyponatraemia. Symptoms range from bloating and nausea to, in severe cases, something far more serious. It has been documented at major marathons where well-meaning runners drank large volumes of plain water. The takeaway isn’t to panic about electrolytes on your average training run — it’s to know that for multi-hour events, replacing some sodium alongside your fluids is sensible.
Electrolyte drinks: what to look for (and what to skip)
If you’ve decided an electrolyte drink is the right call for a session, here’s how to think about it without overcomplicating things:
- Mind the sugar. Many commercial sports drinks lean heavily on sugar for energy, which is useful for very long endurance efforts but excess for most gym or field sessions. Electrolyte tablets or low-sugar mixes dissolved in water tend to be a cleaner option.
- Check the magnesium. Magnesium contributes to electrolyte balance — a specific, authorised claim — and it’s often under-represented in cheaper products. Our magnesium for athletes guide explains why it deserves more attention than it usually gets.
- Don’t ignore potassium. It’s lost in sweat in smaller amounts than sodium, but potassium contributes to normal muscle function, so it’s worth having in any formula you choose.
- Real food works. Coconut water, milk, fruit and lightly salted meals tick many of the same boxes. You don’t always need a packet or a bottle.
Magnesium: the electrolyte worth knowing better
Magnesium sits in a curious position: it’s an electrolyte, it’s lost in sweat, and yet it’s the one most people don’t think about when they think “sports hydration.” The focus tends to go to sodium and potassium. But magnesium contributes to electrolyte balance, to normal muscle function, and to a reduction of tiredness and fatigue — three authorised claims directly relevant to training and recovery.
The broader context is that low magnesium intake is relatively common, particularly in people who train hard or eat in a calorie deficit. If your recovery feels sluggish and your muscles feel heavy even when hydration seems fine, it’s worth checking whether magnesium is part of the picture. Our dedicated magnesium for athletes guide covers intake, forms and food sources in full — it’s worth reading alongside this one.
Putting it together: a practical framework
You don’t need to obsess over electrolytes for every session, but a rough mental model helps:
- Under 60 minutes, moderate intensity: water is enough. Eat well around your session.
- 60–90 minutes, moderate-to-hard effort: consider an electrolyte drink or electrolyte-containing food during or after, especially in the heat.
- Over 90 minutes, high intensity, or in the heat: active electrolyte replacement during exercise is worthwhile — sodium especially, but magnesium and potassium too.
- Very long endurance events (several hours): a deliberate sodium strategy matters; drinking only plain water in large quantities is not the answer.
CapyFuel’s current range covers the other pillars of training support — from pre-workout to rest and recovery — but we don’t currently sell a standalone electrolyte product. This guide exists because understanding what your body actually needs, without the sales pitch, is more valuable than buying something you don’t.
Related: Magnesium for athletes · Vitamin D for athletes · Rest & recovery · Supplements for muscle gain.
Frequently asked questions
Do I need electrolytes for every workout?
Not usually. For sessions under 60 minutes at moderate intensity in normal temperatures, plain water covers you. Electrolytes become genuinely useful for prolonged exercise (roughly 60–90 minutes or more), in hot or humid conditions, or if you sweat heavily and lose a lot of salt. Most gym sessions and short runs don't cross that threshold.
What electrolytes are lost in sweat?
The main ones are sodium, chloride, potassium, magnesium and calcium. Sodium and chloride make up the bulk of what you lose, which is why they feature most in sports drinks. Potassium and magnesium are lost in smaller amounts but still matter — magnesium contributes to electrolyte balance and normal muscle function, and is often the most overlooked of the group.
Can drinking too much water during exercise be dangerous?
Yes, in specific circumstances. During very long endurance events — multi-hour runs or rides — drinking large volumes of plain water without replacing sodium can dilute the sodium in your blood, a condition called hyponatraemia. Symptoms range from nausea and bloating to more serious effects. For everyday training it's not a concern, but for prolonged events, replacing some sodium alongside fluids is sensible.
Is magnesium an electrolyte?
Yes. Magnesium is one of the key electrolytes lost in sweat, and it plays several roles relevant to athletes: it contributes to electrolyte balance, to normal muscle function, and to a reduction of tiredness and fatigue. These are EU-authorised health claims. It tends to get less attention than sodium or potassium, but it deserves a place in any serious conversation about hydration and recovery.