Sodium: Essential Element for Top Performance in Sports

Sodium (lat. Natrium) plays a crucial role in the functioning of the human body. It helps maintain the body’s fluid balance and all cognitive functions. Therefore, it’s important to properly replenish lost sodium, especially during prolonged activities when its losses increase…

What does sodium do?

Sodium is an essential mineral that fulfills many important functions in the human body:

  1. Maintaining fluid balance: Sodium is the main electrolyte in extracellular fluids, such as blood and plasma, where it helps regulate the amount of water in the body and maintain the correct fluid volume​​​​.
  2. Supporting the nervous system: It is key to generating nerve impulses, allowing communication between nerve cells. This enables the proper function of muscles and the nervous system, including the transmission of signals between different parts of the body​​​​.
  3. Absorption and transport of nutrients: It participates in the absorption and transport of some nutrients, such as glucose and amino acids, across cell membranes​​​​.

A lack of sodium can negatively affect performance and overall body function in several ways:

  • Hyponatremia: Low blood sodium levels can lead to hyponatremia, a condition where too much water accumulates in the body relative to the amount of sodium. This can cause swelling, confusion, seizures, and in extreme cases, death​​​​.
  • Changes in blood volume: A lack of sodium can decrease blood volume, straining the heart and worsening the body’s ability to regulate temperature and transport oxygen to muscles​​​​.
  • Muscle cramps and weakness: Sodium is necessary for proper muscle function. Its deficiency can lead to muscle cramps, weakness, and fatigue, which can significantly affect athletic performance​​​​.

Given these roles, it’s important to ensure that sodium levels in the body are optimal, especially for athletes who may lose significant amounts of sodium through sweating during intense exercise.

Individual differences in sodium losses through sweat

The greatest losses of sodium and body fluids occur through sweating, by sweating. Therefore, it is necessary to correctly and timely compensate for these losses during physical activities or exertion.

Sweat rate

The amount of sweat a person sweats per hour, or how quickly one sweats, is called sweat rate. Several factors influence the sweat rate. In a cold environment or during less demanding activities, the sweat rate can be minimal, for example, only 0.3 liters of sweat per hour. Conversely, during intense exercise or in great heat, the amount of sweat can increase up to 2 liters of sweat per hour. The sweat rate therefore tells us how much fluid we should drink per hour. In English, sweat rate is called “sweat rate”.

Relative loss of sodium

Relative loss of sodium is the amount of sodium we lose when sweating out one liter of sweat, thus it is the concentration of sodium in one liter of sweat. During our measurements of sodium concentration in sweat we have encountered individuals losing merely 230 mg of sodium per liter of sweat up to individuals with extreme losses of sodium 2000 mg/l. Relative losses of sodium tell us how strong an ion drink I should drink.

Total loss of sodium

Total loss of sodium is a calculated value from the sweat rate and concentration. The number of liters sweated out is multiplied by the concentration of sodium in the sweat to obtain the total amount of sodium we have lost.

By comparing two extremes of relative losses and sweat rate, we can find that the total differences in losses of sodium and fluids between individuals are huge.

Practical example: A runner with a high relative concentration of sodium in sweat 1,600 mg/l at a higher sweat rate of 1.2 l per hour, will lose during a marathon run (3.5 hours) 6,720 mg of sodium and 4.2 liters of fluids. Another runner with a low relative concentration of sodium in sweat 300 mg/l at an average sweat rate of 0.5 l per hour, will lose during the same activity 525 mg of sodium and 1.75 liters of fluids. The total loss of sodium is thus more than 12 times lower.

If each of these runners wants to deliver a quality performance and speed up the following recovery, then he should use a completely different hydration strategy and definitely drink a different ion drink.


Sodium Losses through Sweat in the Population​
Sodium Losses through Sweat in the Population​​
Data processed and prepared by Iontmax, based on tests carried out during the year 2023.

What happens when sodium losses accumulate?

It is not possible to precisely determine what absolute loss of sodium through sweat begins to be problematic for an athlete. However, it is clear that when losses reach a certain level, it can very negatively affect performance, as well as subsequent recovery.

With increasing loss of fluids and sodium, the volume of blood in the body gradually decreases. This is because sweat is drawn from blood plasma. Reduced blood volume increases the load on the entire cardiovascular system, making it more difficult to pump blood to the skin for cooling the body, and also to the working muscles.

If such fluid losses are not sufficiently compensated for or if there is a significant imbalance between the fluids and sodium intake (e.g., hydration with pure water), other problems may arise, such as overall exhaustion of the body and muscle cramps.

A significant lack of sodium (i.e., electrolyte loss) prevents the brain from transmitting electrical signals that are key to proper muscle control. Without sufficient amounts of sodium, there can be disruptions to the nervous system and communication between the brain and muscles. This can lead to muscle damage and the occurrence of muscle cramps.

For short activities (up to 60 minutes), fluid losses can be compensated with ordinary water. For longer activities, when these losses start to accumulate, it is necessary to replenish the lost sodium, thus preventing an undesirable decrease in blood volume.

Hyponatremia is a condition that occurs when there is a dangerous reduction in the level of sodium in the blood. This condition can occur when sodium intake is insufficient compared to losses through sweat and excessive water intake.

Symptoms of hyponatremia include nausea, vomiting, headaches, dizziness, confusion, cramps, muscle weakness, and even loss of consciousness. In extreme cases, hyponatremia can lead to seizures, coma, or death.

Hyponatremia is a serious medical condition that requires immediate medical attention. Prevention involves adequate sodium intake and balanced hydration during physical activity, especially during prolonged and intensive exercise.

How should I replenish sodium during activity?

Because fluid and sodium losses are very individual, any general guidelines regarding sodium and fluid replenishment should be taken with caution. It’s about those: “Have our ion drink, 600 ml per hour and you’re cramp-free, our ion drink is the best.” – It doesn’t work like that.

An appropriate ion drink is, however, the best way to replenish fluid and sodium losses!

The best starting point for choosing the right ion drink is determining the concentration of sodium in sweat followed by calculating the sweat rate (the amount of sweat lost). These two basic pieces of information are absolutely crucial for proper hydration of the body.

  1. My sodium losses through sweat, or what exactly should I drink? We divide these losses at IONTMAX into 4 groups into low 500 mg/l, medium 1,000 mg/l, high 1,500 mg/l, and very high 2,000 mg/l. If you want to estimate your losses qualifiedly, try our Hydration Plan for FREE. If you want to measure your losses precisely, you can book a Sweat Sodium Concentration Measurement. Subsequently, based on the findings, we determine the level (“strength of the ion drink”) suitable for replenishing sodium and fluids. You will have your ion drink tailored to you.
  2. Sweat rate, or how much should I approximately drink? The sweat rate changes according to the conditions in which you perform the activity and ranges from 0.5 to 2 liters of sweat per hour. Fill in the form Hydration Plan for FREE, and we will prepare a hydration plan for you for free in which you will find instructions on how to easily determine your sweat rate.

The concentration of sodium in sweat is genetically determined, does not change significantly over life or only very little and definitely not abruptly. In most cases, therefore, only one measurement in a lifetime is sufficient.

Iontmax as the first in the Czech Republic offers non-invasive measurement of sodium concentration in sweat. You can learn all about this testing and measurement here: Measurement of Sodium Concentration in Sweat.

More about sodium intake you could find here:

Effects of Sodium Intake on Health and Performance in Endurance and Ultra-Endurance Sports

Training Peaks: Why Athletes Need Sodium


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