And what to do about it to improve performance and recovery. 

When you sweat during exercise, you don’t just lose water; you lose sodium and other key electrolytes.

After a long run or intense training session, you may have noticed white, salty streaks on your skin or clothes. This is evidence that your body loses more than just water when you sweat.

The problem is that most athletes only replace fluids, not sodium and electrolytes. Failure to replace sodium and electrolytes, especially during intense or prolonged exercise, can cause fatigue, muscle cramps, dizziness, or more serious conditions.

This article explains how much sodium you lose in sweat and how to replace it to improve performance and fast-track recovery. 

What you will learn:

  • Why sodium (and other electrolytes) are essential for athletes 

  • How to calculate your sweat rate to improve performance and recovery

  • When to use electrolytes and sodium supplements

Why is sodium important for athletes?

Intense exercise and warm or hot and humid weather induce sweat production. Sweat contains water and electrolytes, including sodium. Water and sodium must be replaced to establish normal total body water [3].

A mismatch between sodium and fluid balance can cause many problems, including exercise‑associated hyponatraemia (EAH). This is when you drink too much water and not enough sodium, defined as a plasma sodium concentration below the normal range during/after exercise [2]. 

Symptoms of EAH include:

  • Nausea

  • Headache 

  • Fatigue 

  • Dizziness

  • Vomiting 

  • Bloating


More severe symptoms may cause confusion, agitation, seizures, or even a coma. Excessive water intake during exercise dilutes blood sodium levels. Athletes participating in longer events, like ultra marathons, are usually more at risk of EAH symptoms, both mild and severe.

How to calculate sodium loss in sweat? 

Endurance athletes may benefit from a sweat test to determine the concentration of sodium in their sweat.

The higher the concentration, the more sodium you lose and therefore the more sodium you should replace with a proper hydration strategy.

You can do a sweat test, whereby you measure the amount of sodium lost during exercise using a sweat patch or a sweat sample, allowing you to tailor hydration and electrolyte replacement to your individual needs.

A sweat test can help you determine if you’re a salty sweater. It can also give you much more accurate fluid and electrolyte intakes to fuel your performance.

However, while sweat patches are an option, conducting a sweat test by yourself can be difficult. Therefore, for the most accurate results, I would recommend working with a professional sports nutritionist or exercise physiologist. 

How much sodium do you lose in sweat per hour?

Sodium loss is highly individual. One athlete may lose 230mg/hour while another may lose an excess of 1,000mg/hour.

Your sweat rate and concentration of sodium determine how much you lose.

Hot and humid temperatures increase sweat rate, causing greater fluid and sodium losses (as well as other electrolytes).

To ensure proper hydration to support performance and recovery, a sweat test can determine how much sodium you lose per hour of exercise in a variety of conditions, allowing you to tailor your hydration and sodium/electrolyte replacement strategy for the best results.

What about other electrolytes?

During exercise, you don’t just lose water and sodium. You also lose other key electrolytes, including:

  • Magnesium 

  • Potassium

  • Calcium 

These electrolytes are essential for supporting proper muscle and nerve function as well as regulating fluid balance [1]. They also play key roles in fatigue management and help sustain endurance and speed up recovery after exercise.

To sustain proper hydration and fluid balance during exercise, use SLT07. It perfectly mimics the ratio of electrolytes in human sweat with added sodium to ensure rapid rehydration while preventing muscle cramping.

If you’re a particularly salty sweater or are participating in a longer event, like an ultra endurance cycling event or run, consider SLT+, which is made for demanding conditions and hot climates to support performance and promote faster recovery.

For more guidance on when to take electrolytes (before, during, and after exercise), see our practical guide with advice from a qualified sports dietitian.

Do you need electrolyte drinks or tablets?

Jena Brown, an endurance dietitian and owner of Victorem Performance Nutrition in Brenham, Texas, explains that your daily diet and fueling plan influence how much sodium and electrolytes you need.

“Athletes who consume more processed foods typically get higher sodium intakes and may need less from electrolyte mixes, while those following a whole-food-focused diet naturally get less sodium and may benefit from additional supplementation.” 

However, don’t use this as an excuse to follow a diet made up of exclusively processed foods. Fuel for performance.

Most athletes are likely to benefit from electrolyte supplementation, especially during long runs, rides, or other exercise that exceeds 75 minutes, and definitely exercise that lasts upwards of 4 hours.

Taking electrolytes during exercise is even more important for long and multi-day events. An electrolyte imbalance or deficiency increases fatigue and reduces recovery ability.

Key takeaways

  • When you sweat, you don’t just lose water; you lose sodium and other electrolytes 

  • Failure to replace sodium and key electrolytes can lead to a fluid imbalance, causing muscle cramps, fatigue, dizziness, and other more serious symptoms

  • Sodium plays a key role in proper hydration, muscle function and nerve signalling

  • Consider taking electrolytes before, during, or after exercise to support your performance and recovery

  • Conduct a sweat test with a sweat patch or laboratory test to find out how much water, sodium, and other electrolytes you lose during sweat 

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References

  1. Lindinger, M.I., 1995. Potassium regulation during exercise and recovery in humans: implications for skeletal and cardiac muscle. Journal of molecular and cellular cardiology, 27(4), pp.1011-1022.

  2. McCubbin, A.J., 2025. Sodium intake for athletes before, during and after exercise: review and recommendations. Performance Nutrition, 1(1), pp.1-22.

  3. Shirreffs, S.M. and Sawka, M.N., 2011. Fluid and electrolyte needs for training, competition, and recovery. Journal of Sports Sciences, 29(sup1), pp.S39-S46.