Why sodium plays such an important role in exercise

February 16th 2022

Why sodium plays such an important role in exercise

Your body consists of water by around 50-70 %. One third of that water exists outside of your cells, in extracellular fluids like blood - two thirds inside of your cells.

The main electrolyte in this extracellular fluid is sodium and much of your body’s total sodium reserves are found here. This makes it rather salty and the total volume of extracellular fluid in your body is directly related to the amount of sodium you have on board at any given time. So, more sodium equals more fluid; less sodium means less fluid.

As well as maintaining fluid balance, sodium plays an important role in the absorption of nutrients in the gut, maintaining cognitive function, nerve impulse transmission and in muscle contraction.

Most of the sodium we consume is in the form of sodium chloride, or the common table salt found in food and drinks. Our bodies can’t produce or store it beyond a certain point, so we depend on consuming it daily to keep our sodium levels up.

The main way athletes lose sodium and fluid is sweating. It is important to notice that everyone loses a different amount of sodium in their sweat. Some sweat so much that they get salt rims on their clothing after training. Others have very little sodium concentrations in their sweat. The average concentration ranges between 200 to 2300 mg/l sweat.

Serious sodium loss

It’s obviously not possible to nail down the exact point at which sodium (and fluid) loss through sweating becomes a problem for an athlete. But it must be logical that when losses reach a certain point, the effects can be detrimental to your performance and in the worst case even to your health.

Your blood volume is gradually reduced as your sweat losses increase – that’s because sweat is drawn from your blood plasma. The thicker your blood gets, the harder it is for it to flow through your veins, to your skin and to your working muscles.

Other symptoms such as fatigue and muscle cramps are also a consequence of a further loss or an imbalance between sodium and fluid.

That’s why consuming plain water can be counterproductive, as it dilutes the sodium concentration even further and leads to hyponatremia.

Sweat and especially sodium loss quantity is so individual, that it’s impossible to give recommendations that solve the problem. The two main parameters that should be measured are the total amount you sweat and your sweat sodium concentration.

The sodium concentration in your sweat is largely genetically determined and varies when your performance level increases.

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