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On this sequence of weblog posts we’ve mentioned what sodium is, what it does within the physique, the way it’s misplaced in sweat, and tips on how to quantify these losses. On this publish, we’ll focus on tips on how to determine if sodium wants changing throughout train, and whether or not a focused method is critical or not.

Sodium decision chart

Why do we have to substitute sodium?

As mentioned in a earlier publish, sodium consumed throughout train might have advantages when it comes to:

  • enhancing the style of drinks

  • sustaining blood sodium focus and osmolarity

  • growing blood quantity retention

Presently there’s minimal if any proof that sodium alternative can really enhance train efficiency, not less than train of lower than 4 hours.

Observe that for the explanations described above, the primary doesn’t require sweat sodium testing, merely ‘season to style’. The second purpose is the place quantifying sweat sodium losses is perhaps doubtlessly useful. So when does it matter?

Predicting sodium alternative wants

We don’t at present have laboratory research to inform us how a lot sodium wants changing throughout train. Nonetheless, a mathematical components initially developed for managing water and sodium steadiness in hospital sufferers has been validated efficiently throughout train. In a just lately printed examine, this components was used to estimate how a lot sodium wanted to be consumed to keep up a gentle blood sodium focus (and due to this fact doubtless osmolality as effectively). As seen within the graph beneath, this modelling confirmed clearly the 2 fundamental components that decide the necessity for sodium alternative throughout train:

  • The extent to which sweat fluid losses are changed (i.e. fluid consumption as a % of sweat losses)

  • The sweat sodium focus, which varies within the graph from very low (460 mg/L) to very excessive (1840 mg/L).

Sodium blood concentration infographic

These two components virtually completely decided the % of sweat sodium losses that want changing to keep up a secure blood sodium focus. The extra aggressively fluid is changed, the higher want for sodium. Likewise, these with the next sweat sodium focus have been extra prone to profit from sodium alternative.

What does this imply in the actual world?

Fluid alternative throughout train is designed to forestall dehydration, which is usually outlined because the lack of a sure % of physique weight in fluids. However relying on sweat charge and the length of train, the % of sweat losses that want changing to attain this can fluctuate. Larger sweat charges and longer durations of train enhance the % of fluid losses that want changing to forestall a sure degree of fluid loss. And this helps us decide when focused sodium alternative is perhaps useful, or when the sweat testing course of is pointless.

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In train of lower than 2 hours, the quantity of fluid that wants changing to forestall dehydration is prone to be low, except the sweat charge is extraordinarily excessive. Within the instance above if somebody sweats 0.9 L/h for two hours, they might want to substitute roughly 20% of their fluid losses (a really small quantity of fluid). There could also be different causes as effectively why athletes can’t devour a big share of their losses. There’s a restrict to how a lot fluid will be virtually consumed and tolerated throughout train. There could also be restricted alternatives to drink, and it’s tougher to tolerate massive portions of fluid. So even when athletes have a really excessive sweat charge, it’s unlikely they’ll have the ability to substitute far more than 50% of their fluid losses.

Which means that in these conditions sodium alternative is pointless to keep up a secure blood sodium focus. Sweat sodium testing is due to this fact unlikely to be of worth, and as an alternative athletes in these sports activities can merely select their sodium based mostly on style preferences.

Do I need additional sodium?

The state of affairs could be very completely different for ultra-endurance sports activities, nonetheless. A comparatively decrease sweat charge, however with a very long time for fluid losses to build up and higher alternatives to drink and tolerate fluids, implies that changing a higher % of fluid losses is each needed and doable. It’s in these eventualities that sweat testing and focused sodium alternative could also be extra useful. Bear in mind although from the earlier weblog publish that sweat sodium focus varies from day-to-day, and so very exact sodium alternative is prone to be neither needed or doable.


Presently, the one outlined function for offering a focused quantity of sodium throughout train seems to be to keep up a secure blood sodium focus and due to this fact osmolality, for any given fluid consumption. Because of the nature of sweat losses, blood sodium focus will solely fall when athletes are required (and do) substitute the bulk (>70%) of fluid losses to forestall dehydration, and entire physique sweat sodium focus is above common (>40 mmol/L or 1g/L). Solely in ultra-endurance train is that this prone to realistically happen – in all different instances athletes can merely season to style on the subject of sodium consumption throughout train. On condition that the diploma of fluid alternative is without doubt one of the fundamental determinants of sodium alternative wants, athletes ought to first estimate their sweat fluid losses and alternative wants, earlier than deciding if sweat sodium testing and focused alternative is definitely needed.


  1. Baker LB et al. Quantitative evaluation of serum sodium focus after extended operating within the warmth. J Apply Physiol. 2008; 105(1):91-99.

  2. McCubbin AJ. Modelling sodium necessities of athletes throughout quite a lot of train eventualities – Figuring out when to check and goal, or season to style. Eur J Sport Sci. 2022; DOI: 10.1080/17461391.2022.2083526.

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