Sodium: the key role in athletic performance

Sodium: The Key Role in Athletic Performance – a guest post by Juli Brüning (Part 1/3)

Whether in endurance sports or team competitions, sodium is often underestimated but crucial for optimizing and maintaining athletic performance.¹ As the most important electrolyte lost through sweat during exercise, sodium helps ensure the body functions properly under stress. It regulates fluid balance, supports cognitive function and muscle contraction, aids in nutrient absorption in the gut, and is essential for maintaining blood volume.

Hyponatremia: DNF’s & Underperforming

Everyone knows the stories: athletes – from weekend warriors to elites – spend weeks or even months preparing, every detail perfectly planned, start line energy buzzing – only for the race to end in a disappointing “DNF” (Did Not Finish). A 2015 study found that gastrointestinal issues are the most common reason for DNFs, accounting for 35.6%.² Nausea, vomiting, stomach cramps, diarrhea, bloating – race day can quite literally fall apart. And it’s not just about incorrectly dosed gels, bars, or carb sources. An imbalance in fluid and sodium intake plays a major role here too.

The same applies to "underperforming" during a race: muscle cramps, elevated heart rate with reduced output, heavy legs, heat-related issues, or mental fog. Even without a DNF, the result falls far short of expectations.

The Basics: What does sodium actually do?

Our bodies are made up of 50–70% water. About one third of that is found outside the cells (e.g., in blood plasma) and makes up the extracellular fluid – from which sweat is produced. This is exactly where sodium plays a central role. It helps maintain blood fluid volume – essential for proper blood supply to the digestive system for nutrient uptake, for temperature regulation and sweating as a cooling mechanism, and for the transmission of electrical signals, especially in muscle contraction.³

Sodium helps the body retain more fluid. Less sodium = less fluid retention = faster dehydration.

So when you sweat, you’re not only losing water but also sodium – and if that isn’t replaced in the correct concentration, it can negatively impact your performance. This is especially true for long efforts or in warmer conditions – but even in short events, proper hydration is critical for peak performance.⁴

A sodium deficiency due to sweat loss or overconsumption of plain water can dilute the sodium concentration in blood plasma and lead to dangerous conditions like exercise-induced hyponatremia (critically low sodium in the blood).⁵

Our bodies can’t produce sodium or store it beyond a certain level. That means regular intake is crucial – especially for athletes with high sweat loss and salty sweat!

Sweat Sodium Concentration vs. Sweat Rate: Two Factors That Define Your Hydration Strategy

Sweat sodium concentration refers to how much sodium (and other electrolytes) you lose per liter of sweat. Other electrolytes like magnesium, calcium, and potassium are also lost, but in much smaller amounts. Sweat sodium concentration is measured in milligrams per liter (mg/L) and can be determined with a special sweat test.

Sweat rate, on the other hand, refers to how much fluid (sweat) you lose while exercising. This is influenced by environmental factors (temperature, humidity, wind), exercise intensity, and clothing. Sweat rate is measured in milliliters or liters per hour and can be estimated by comparing pre- and post-workout body weight.

Both sweat sodium concentration and sweat rate vary greatly between athletes.⁶ Unlike sweat rate, which fluctuates based on conditions, your sweat sodium concentration is largely genetic and remains relatively stable during adulthood. That means it usually only needs to be tested once.

To define your optimal hydration strategy, you need to answer two questions: How much do I sweat per hour (ml or L/h), and how salty is my sweat – i.e., how much sodium do I lose per liter of sweat (mg/L)?

Sweat sodium concentrations vary greatly among athletes:

Some lose less than 200 mg of sodium per liter of sweat
Others may lose over 2,300 mg per liter
The average is around 950 mg/L, as confirmed by large-scale studies.^7,8

These individual differences show why a "one-size-fits-all" hydration approach doesn’t work.

Athletes with low, moderate, or high sweat sodium concentrations:

Athletes measuring sweat sodium concentration Figure 1: Individual differences in sweat sodium concentration in athletes. Adapted from Asker Jeukendrup, mysportscience.⁹

The Sweat Test: How ‘Salty’ Are You?

There are some common signs that may indicate you’re a salty sweater:

Salt stains on clothing, running vests, race suits, caps, or on your face and eyebrows,
Salty-tasting sweat, stinging in your eyes or wounds when sweat gets in,
Frequent cravings for salty foods,
Recurring cramps after long/hard workouts in heat,
General underperformance in hot conditions, or
Extended recovery time after workouts and races.

No single symptom confirms you’re a salty sweater, but if several apply to you, it’s highly likely! Based on this, you can estimate your "saltiness" using the saltyness scale.

Figure 2: "Saltyness Scale" – Individual sweat sodium concentration. Adapted from Precision Hydration Ltd.

If you want to know your exact sweat sodium concentration, you can take a sweat test at a Precision Fuel & Hydration Sweat Test Center. This technology has long been used in medical diagnostics, such as for cystic fibrosis testing.

The sweat test is completely painless and non-invasive, done at rest, and provides an accurate reading of your sweat sodium concentration in mg/L. Based on the result, you’ll get a personalized recommendation for the right electrolyte strength in training and racing. A tailored hydration approach can make a huge difference in performance. Just look at top athletes like Hayden Hawks (HOKA), Robbie Britton (PF&H), Caitlin Fielder, Tabor Hemming (adidas TERREX), and in triathlon Emma Pallant-Browne. Side note: Hayden took 45 electrolyte capsules during his 2024 Western States podium finish – 11,250 mg sodium, customized to his needs. That shows just how important electrolyte balance is. Even without a sweat test, you can improve your hydration strategy using the symptoms and saltyness scale above. Pay attention to the sodium content in sports nutrition and electrolyte tablets (e.g., PH500 = 500 mg/L, PH1000 = 1,000 mg/L, PH1500 = 1,500 mg/L from Precision Fuel & Hydration). (More tips for practical implementation in the blog Part 2/3 on "The Optimal Hydration Strategy for Training & Racing".)

Optimal Sodium Intake:

Optimal sodium intake depends on your individual sweat sodium concentration, sweat rate, training intensity, and environmental conditions. A general rule is to match your drink's sodium concentration with the sodium you lose in sweat. For example, if you lose 1,000 mg/L, then aim for 500 mg of sodium per 500 ml of fluid – and scale the total fluid intake to match your sweat rate. You’ll find more on this in the upcoming blog on “Fluid Intake During Exercise”.

In summary, a balanced sodium intake is key for:

Prevention of dehydration and overhydration
Reduction of the risk of exercise-induced hyponatremia¹⁰
Relief from muscle cramps, particularly for athletes prone to cramps¹¹
Maintenance of efficient body cooling mechanisms, especially in hot conditions
Improvement of fluid retention and absorption
Prevention of performance declines and gastrointestinal issues caused by electrolyte and fluid imbalances

Too much salt can also be dangerous! Taking salt capsules recklessly can cause nausea, bloating, and edema (which can also occur with hyponatremia). In extreme cases, it can lead to intense thirst, which results in excessive fluid intake, potentially triggering hyponatremia. Stay mindful and listen to your body: If you're craving salt, slightly increase your sodium intake, but reduce it if you're craving plain water.

Conclusion

To personalize your hydration strategy, measuring sodium loss through a sweat test is ideal. Alternatively, questionnaire-based studies have shown that subjective assessments of sweat sodium content and rate can provide an initial guide⁷. While accurately measuring sweat sodium concentration is preferred, a well-informed estimate can serve as a great alternative if testing is not feasible due to cost or logistical reasons. Whether measured or estimated, an individualized hydration strategy is valuable for every athlete. It's important to remember that too much sodium intake can also be problematic. Sodium intake should therefore be adjusted individually and discussed with a nutrition expert or sports physician.

¹ Del Coso J, González-Millán C, Salinero JJ, Abián-Vicén J, Areces F, Lledó M, Lara B, Gallo-Salazar C, Ruiz-Vicente D. ‘Effects of oral salt supplementation on physical performance during a half-ironman: A randomized controlled trial’. Scand J Med Sci Sports. 2015 Feb 14. doi: 10.1111/sms.12427.

² Stuempfle KJ, Hoffman MD. Gastrointestinal distress is common during a 161-km ultramarathon. J Sports Sci. 2015;33(17):1814-21. doi: 10.1080/02640414.2015.1012104. Epub 2015 Feb 26. PMID: 25716739.

³ Hydration and cooling in elite athletes: relationship with performance, body mass loss and body temperatures during the Doha 2019 IAAF World Athletics Championships. Racinais S, Ihsan M, Taylor L, Cardinale M, Adami PE, Alonso JM, Bouscaren N, Buitrago S, Esh CJ, Gomez-Ezeiza J, Garrandes F, Havenith G, Labidi M, Lange G, Lloyd A, Moussay S, Mtibaa K, Townsend N, Wilson MG, Bermon S. Br J Sports Med. 2021 Dec;55(23):1335-1341. doi: 10.1136/bjsports-2020-103613.

⁴ Sanders B et al. Sodium replacement and fluid shifts during prolonged exercise in humans. Eur J Appl Physiol. 2001; 84(5):419-425.

⁵ Hiller WD. Dehydration and hyponatremia during triathlons. Med Sci Sports Exerc. 1989;21(5 Suppl):S219–21.

⁶ Baker LB. Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability. Sports Med. 2017; 47(Suppl 1):111-128.

⁷ Ranchordas, M.K., Tiller, N.B., Ramchandani, G. et al. Normative data on regional sweat-sodium concentrations of professional male team-sport athletes. J Int Soc Sports Nutr 14, 40 (2017).

⁸ Baker LB, Barnes KA, Anderson ML, Passe DH, Stofan JR. Normative data for regional sweat sodium concentration and whole-body sweating rate in athletes. J Sports Sci. 2016;34(4):358-68. doi: 10.1080/02640414.2015.1055291. Epub 2015 Jun 12. PMID: 26070030.

⁹ Jeukendrup, A. (JAHR). How much do you sweat and how much sodium do you lose? [Abb. 1]. Mysportsscience. https://www.mysportscience.com/post/how-much-do-you-sweat (zuletzt abgerufen am: 12. 03.2025).

¹⁰ Exercise-Associated Hyponatremia: 2017 Update. Hew-Butler T, Loi V, Pani A, Rosner MH. Front Med (Lausanne). 2017 Mar 3;4:21. doi: 10.3389/fmed.2017.00021.

¹¹ Horswill CA, Stofan JR, Lacambra M, et al. Sodium balance during U. S. football training in the heat: cramp-prone vs. reference players. Int J Sports Med. 2009;30(11):789–79.

Figure List:

Cover Image: SALTY Trailrunning.(https://www.saltytrailrunning.com/)

Figure 1: Individual differences in sweat sodium concentration in athletes.

Figure 2: "Salytness Scale" - Individual sweat sodium concentration.

Juli Brüning

Juli is a nutritionist (M.Sc.), Performance Nutritionist, and Ultra Trailrunner for the Craft Elite Run Team Germany. She supports athletes in all sports and nutrition-related topics and works as a Sweat Test Center and Athlete Support for Precision Fuel and Hydration.