Why Electrolytes Matter in Endurance Performance

The Speed Read

When we discuss electrolytes in endurance sports, we typically mean sodium, potassium, magnesium, and chloride. They are more than just “salts.” They’re essential minerals that keep your muscles firing, your nerves functioning, and your hydration in balance. We can lose these in large amounts during endurance exercise; understanding how to replace electrolytes can be the difference between finishing and collapsing.

Electrolytes: The Unsung Heroes of Performance

Carbohydrates, water, and electrolytes are the key pillars of endurance performance. Electrolytes are minerals that carry an electric charge in the body. They regulate muscle contraction (including the heartbeat), nerve signalling, fluid balance inside and outside cells, and pH levels in the body.

When you sweat, you lose both water and electrolytes, especially sodium. The more you lose, the greater the risk of cramps, fatigue, dizziness, or even hyponatraemia (dangerously low blood sodium). For endurance athletes, electrolyte replacement isn’t optional — it’s performance-critical.

The Science of Sweat and Sodium

Not all sweat is equal. Sweat rates range from 0.5 L/hour to more than 2.5 L/hour depending on body size, intensity, environment, and genetics. Sweat sodium concentration also varies widely: some athletes lose 400 mg sodium per litre of sweat, while others lose over 1,500 mg/L (Baker, 2017).

This means two athletes can finish the same race in the same heat, but one will be in far greater electrolyte debt than the other.

“My sweat contains a high concentration of sodium per litre (over 1,500 mg). I could lose 2.5 litres of sweat per hour in humid conditions, which meant I was losing nearly 4 grams of sodium per hour, equivalent to around 10 grams of salt. If I hadn’t managed electrolytes carefully, I wouldn’t have been able to finish, let alone compete.”

Research shows that even moderate sodium losses impair performance. Sodium helps the body retain fluid, so without it, water intake alone [dilutes] blood sodium further and increases the risk of hyponatraemia (Hew-Butler et al., 2015). Replacing both fluids and sodium is therefore critical.

Why Electrolytes Matter for Endurance Athletes

Electrolytes maintain hydration balance by facilitating water absorption in the small intestine and promoting the body’s ability to retain fluid (Sawka et al., 2007). They reduce the risk of cramps and neuromuscular fatigue, although cramping is a multi-factorial phenomenon; sodium and magnesium are central to muscle firing and relaxation.

They also support energy delivery by helping regulate carbohydrate transport and utilisation. Without balance, fuel uptake is impaired. And beyond performance, chronic low sodium from repeated long sessions without replacement can compromise blood pressure regulation and overall health (Hoffman & Stuempfle, 2014).

In short, electrolytes are as essential as carbohydrates for going the distance.

Practical How-To: Using Electrolytes in Training and Racing

The right electrolyte strategy depends on session type, duration, and environmental conditions. For short, easy sessions in cool conditions, water is usually enough, though a low-dose electrolyte drink can support day-to-day hydration. For moderate sessions in temperate conditions, electrolytes are advantageous when the sweat rate is high or the intensity is sustained.

At truefuels, we label our solutions with the quantity of salt they contain. The electrolyte and high-salt performance gels both contain 1 g of salt, or approximately 400 mg of sodium.

For long endurance sessions over 90 minutes, electrolytes are essential and should be paired with carbohydrate fuelling. There is debate about exactly how much sodium we need to replace, but to me there doesn’t seem to be a disadvantage to trying to replace [the majority] of the sodium that we lose. I aim to replace about 1 g of salt for each litre I lose in sweat. You could adjust this higher if you’re a salty sweater, or lower if you’re a light sweater with low sodium concentrations. In hot and humid environments, sodium needs may exceed 1,000 mg/L ([2.5 g of salt/L]) — use electrolytes in every bottle, don’t rely on water alone. For hot races, I would “pre-load” with sodium the day before and on the morning of the race.

Even shorter interval sessions in the heat benefit from electrolytes, as the combination of high sweat rate and dehydration risk makes sodium crucial. And on multi-session days, electrolytes between workouts accelerate rehydration and recovery so the second session doesn’t suffer.

Building an Electrolyte Routine

A simple framework works for most athletes. Start hydrated — aim for pale straw-coloured urine in the morning. In hot conditions, add electrolytes to water the evening before key sessions to boost sodium stores. During long or hot sessions, combine electrolytes with carbohydrate every hour. After training, replace the fluid lost in sweat with around 1 g of salt per litre to improve retention. Above all, practise consistently. Just like gut training with gels, the electrolyte strategy must be rehearsed in training, not left to race day.

Personally, I take electrolytes during every session. If I am using Carbohydrates because the session is intense or long, I get them from the performance gel and an electrolytes sachet in my other bottle. For a low-intensity session, I’ll often go out with two bottles with an electrolyte sachet in each. They taste great, and I get the minerals I need.

Conclusion: Small Minerals, Big Impact

Electrolytes might not get the same attention as carbohydrates or protein, but in endurance sport, they’re just as important. They keep your muscles firing, your hydration balanced, and your performance steady.

By understanding your sweat rate, practising in training, and using electrolytes intelligently across different sessions and conditions, you can remove one more variable from race day. Don’t leave your hydration to chance. Make electrolytes part of your fuelling strategy, and be your best.

References

Baker, L.B. (2017). Sweat testing methodology in exercise science: A review. Sports Medicine, 47(Suppl 1), 111–128.

Casa, D.J., Stearns, R.L., Lopez, R.M., Ganio, M.S., McDermott, B.P., Yeargin, S.W. and Maresh, C.M. (2010). Influence of hydration on physiological function and performance during trail running in the heat. Journal of Athletic Training, 45(2), 147–156.

Hew-Butler, T., Rosner, M.H., Fowkes-Godek, S., et al. (2015). Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference. Clinical Journal of Sport Medicine, 25(4), 303–320.

Hoffman, M.D. and Stuempfle, K.J. (2014). Hydration strategies, electrolyte balance, and exercise-associated hyponatremia. Sports Medicine, 44(Suppl 1), 79–87.

Sawka, M.N., Burke, L.M., Eichner, E.R., Maughan, R.J., Montain, S.J. and S