Magnesium, Potassium and Sodium for Athletes

A bottle can look like a hydration plan and still leave you under-fuelled, cramping, nauseous or fading late in a race. Magnesium, potassium and sodium for athletes are often discussed as one category, but they do not do the same job during endurance exercise. Sodium is the electrolyte you lose in the greatest quantity through sweat and the one that most often needs deliberate replacement. Potassium and magnesium matter too, but their best use is more nuanced than simply adding more to every bottle.

For runners, cyclists and triathletes, the aim is not to consume the longest electrolyte label. It is to match fluid, sodium and carbohydrate intake to the demands of the session, then use food and recovery nutrition to cover the wider mineral picture.

"Sodium is the variable most athletes ignore until it costs them. Potassium and magnesium matter — they do real work in the body — but they don't replace sodium's role in fluid balance during prolonged sweating. The mistake is treating electrolytes as one undifferentiated category and buying the product with the longest ingredient list. What matters is getting the right amounts of the right minerals at the right time, matched to what you're actually losing."
— Alistair Brownlee, Two-time Olympic Triathlon Champion and founder of truefuels

Magnesium, potassium and sodium for athletes: different roles

Sodium helps retain fluid in the body, supports normal nerve signalling and muscle contraction, and encourages drinking when it is included in a palatable sports drink. It is also the mineral most directly linked to sweat losses. In a long race, particularly in warm conditions, replacing some of that sodium is central to maintaining a workable hydration strategy.

Potassium works alongside sodium in fluid balance and electrical signalling within cells. It is essential to normal muscle and nerve function, but sweat losses are generally far lower than sodium losses. Most athletes can cover their potassium needs through a consistently good diet containing foods such as potatoes, beans, yoghurt, fruit, vegetables and grains. A sensible amount in a drink can contribute, but it is rarely the main lever on race day.

Magnesium supports hundreds of processes in the body, including energy metabolism, protein synthesis and normal muscle and nerve function. It has a deserved place in an athlete's overall nutrition. Yet it is not a fast-acting anti-cramp ingredient, and high doses during exercise can create the very problem athletes want to avoid: gastrointestinal distress. Magnesium is usually better treated as a daily nutrition and recovery consideration, not a reason to overload a race bottle.

That distinction matters. A well-executed endurance plan prioritises what the body is losing, what it can absorb under pressure, and what will stay down when intensity rises.

Start with sodium, not a generic electrolyte total

Two athletes can complete the same summer long run with very different sodium requirements. Sweat rate, sweat sodium concentration, duration, temperature, humidity, clothing, pace and acclimatisation all change the equation. White salt marks on kit, stinging sweat in the eyes and a very salty taste can suggest higher sodium losses, but they are clues rather than a precise diagnosis.

For many endurance sessions, around 300–600 mg of sodium per hour is a practical starting range. Athletes training or racing for several hours in heat, those with high sweat losses, and known salty sweaters may need 600–1,000 mg per hour or more. The correct figure depends on the athlete and conditions, not on the most aggressive number seen online.

Fluid intake must sit alongside this. Drinking large volumes of plain water while replacing little or no sodium can dilute blood sodium concentration. At the other extreme, taking concentrated sodium without enough fluid can be unpleasant and may not solve the problem you think it will. Drink to a planned range informed by your sweat rate and conditions, then test it repeatedly in training.

A useful field method is to weigh yourself before and after a representative session, accounting for fluid consumed. A modest body-mass loss may be acceptable, but a large drop indicates that your fluid plan needs attention. Do not chase a perfectly unchanged body weight at all costs. Overdrinking is a performance and safety risk too.

Use conditions to adjust the plan

On a cool 75-minute run, water and a normal meal pattern may be sufficient, depending on your pace and individual needs. On a three-hour ride in warm weather, sodium becomes a more deliberate part of every hour. On a marathon, an athlete who has trained with 700 mg of sodium per hour should not suddenly switch to plain water at every aid station because it feels simpler.

Think in hourly totals rather than isolated products. Add up the sodium in your drink, gels, chews and any capsules. Then compare that total with your fluid and carbohydrate plan. Precision prevents accidental under-dosing, but it also prevents doubling up.

Where potassium fits in a race plan

Potassium belongs in the system, but it does not need to dominate it. Sports drinks commonly provide modest amounts because potassium contributes to electrolyte balance and because athletes lose some through sweat. This is useful, particularly across long days of training or multi-stage events.

What potassium cannot reliably do is rescue a poorly built hydration plan. If you are losing large amounts of sodium, consuming extra potassium will not replace sodium's role in extracellular fluid balance. Likewise, a mid-race banana is not a substitute for a sodium strategy when the day is hot and the event is long.

Prioritise potassium across the full week. Eat enough total energy, include carbohydrate-rich whole foods, and do not treat race nutrition as the only source of minerals. If you use electrolyte products, choose a formulation with a sensible balance rather than one that turns potassium into a headline at the expense of sodium.

Athletes with kidney disease, heart conditions, or medicines that affect potassium levels should seek personalised clinical advice before using potassium supplements. More is not automatically better.

truefuels Active Hydration

390mg sodium, 150mg potassium and 25mg magnesium per sachet — the right minerals at the right amounts. No artificial sweeteners or preservatives. Formulated from GSSI and NIH sweat science to match what endurance athletes actually lose.

See Active Hydration →

Magnesium: valuable, but not a mid-race fix

Magnesium is frequently marketed as the answer to muscle cramps. The evidence is less tidy. Exercise-associated muscle cramps are often linked to fatigue, pacing, neuromuscular control and individual susceptibility. In some situations, inadequate fluid or sodium may contribute. A magnesium tablet swallowed at the first twitch is not a dependable solution.

For most endurance athletes, magnesium is best addressed through regular diet quality and, where appropriate, a well-tolerated supplement taken away from key training and racing. Nuts, seeds, pulses, wholegrains, leafy greens and cocoa all contribute. If your diet is restricted, your training load is high, or a clinician has identified low magnesium status, supplementation may be appropriate.

The trade-off is digestive tolerance. Some forms and larger doses can have a laxative effect, which makes them a poor experiment before a hard session, long run or start line. Never trial a new magnesium product during race week. Consistency beats novelty.

Build an electrolyte protocol that works under pressure

Your plan should be simple enough to execute when you are tired, hot and making decisions at pace. Start by defining the event conditions and your likely duration. Set a carbohydrate target, a fluid range and a sodium-per-hour target. Only then select the combination of drink mix, gels and other products that delivers those numbers without overwhelming your stomach.

For a 2–3 hour event in mild conditions, an athlete might use a drink providing 400–600 mg of sodium per hour, plus carbohydrate from drink and gels. In warmer weather or for a high-sweat athlete, that sodium target may rise while fluid intake rises with it. Potassium can remain a modest supporting component. Magnesium does not need to be pushed during the event if daily intake is already adequate.

Practise the plan at race intensity, not only on easy days. Gut tolerance changes when blood flow is directed towards working muscles, when the temperature climbs, and when carbohydrate intake approaches race-level targets. Test the exact product concentration, bottle size, aid-station routine and timing you expect to use.

truefuels approaches this as one system: fuel for carbohydrate delivery, hydration for sodium-led fluid management, and a protocol built around the conditions you will actually face. The point is not complexity. It is removing decisions from the hardest kilometres of the day.

Common mistakes that cost athletes late in the race

The first mistake is treating every electrolyte as interchangeable. Sodium is usually the priority during prolonged sweating; potassium and magnesium support the wider picture but do not replace it. The second is following a fixed plan regardless of temperature. A cool spring race and a humid summer race may require very different fluid and sodium intakes.

Another common error is relying on thirst alone after the session has become demanding. Thirst remains useful, but it may not be enough to guide a high-stakes long event, particularly when access to fluids is irregular. Finally, athletes often add several products without counting their combined sodium or carbohydrate. A precise plan can still be simple, provided you know what each serving contributes.

The best hydration strategy is the one you can absorb, repeat and trust. Build sodium around your sweat losses and the day's conditions, keep potassium and magnesium in their proper supporting roles, and rehearse the whole plan until it feels automatic when performance matters.

Electrolytes built for endurance — not marketing.

390mg sodium from Himalayan Rock Salt per sachet. No artificial sweeteners or preservatives. Formulated from GSSI and NIH sweat science to match real sweat losses.