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Why sodium is crucial for maintaining your performance.


You can't get filthy without getting sweaty. That’s why we’ve teamed up with Precision Hydration to bring you a series of articles aimed at helping you stay properly hydrated when you’re out doing what you love. PH have personalised the hydration strategies of a long list of elite athletes such as Downhill MTB World Champ Tracy Moseley and World Solo 24hr Single speed World Champ Steve Day, so you’re in good hands.

Hydration advice is not all we’ve hooked you up with. Take PH’s online Sweat Test to get a free personalised hydration plan with advice on what, when and how much to drink when you’re out sweating and they’ll send you afree £10 voucher to use to get electrolyte supplements that match how you sweat.

Right then, the first blog in our #GetFilthyGetSweaty series talks you through why replacing the sodium you lose in your sweat is so important if you want to perform at your best…


Well, sodium plays a number of important role s in your body. It aids in the absorption of nutrients in your gut, maintaining cognitive function, nerve impulse transmission and muscle contraction. But, from an athletes point of view at least, perhaps the most critical function it plays is in helping you maintain a fluid balance in your body.

Sodium is the main electrolyte found in your blood. Your blood makes up 15-20% of the extracellular fluid in your body (about 5l in the average adult), so much of your body’s total sodium reserves are found here.

What that sodium does is help you absorb and retain more of the fluid you take in and this boosts your blood plasma volume. The more blood you have, the less strain on your cardiovascular system as it works to deliver oxygen to your muscles and dissipate heat to cool you down when you’re working hard. Basically, sodium’s pretty important if you want to maintain your performance when it counts.


When you go to the toilet and when you sweat, you lose sodium from your body. Because the body can’tmanufacture sodium or store it beyond a certain point, you need to consume it every day to keep your levels topped up.

Sweating is the main way athletes lose sodium and fluids during exercise. That's why those of us who train regularly have different needs when it comes to replacing sodium than those who don't.

The thing is, everyone loses a different amount of sodium in their sweat, from as little as 200mg of sodium per litre of sweat, to as much as 2,000mg/l. And everyone sweats at different rates, which means that your net sodium losses could be as much as 10x higher than the person next to you on the start line.

And, in a lot of cases, those losses are many times higher than someone who is not sweating on a regular basis. This is why the standard government guidelines for sodium consumption should be viewed cautiously by athletes who train a lot. It's more than possible to lose the 2,300mg of sodium recommended by the existing government guidelines in just 1 hour of exercise, if you’re sweating heavily and you're sweating out lots of sodium.

I personally lose about 1,842 mg/l - which puts me firmly in the ‘salty sweater’ camp - and I often suffered from cramp and other hydration-related issues in hot climates as a result.


Your blood volume is gradually reduced as your sweat losses increase because sweat is drawn from your blood plasma. This increases the strain on your cardiovascular system, making it harder to pump blood to your skin (to cool you down) and to your working muscles. This obviously has a negative impact on your performance.

Other issues like a general feeling of fatigue, a loss of concentration and even muscle cramps can also be experienced if losses are allowed to go uncorrected for long enough. If you’re someone who suffers from cramp after you’ve been sweating for a while, keep your eyes peeled for a future blog on the causes of cramp in our #GetFilthyGetSweaty series.

Up to a certain point, taking in plain water is enough to mitigate sweat losses. But, as those losses start to mount up, you need to replace sodium too to avoid your blood becoming diluted. This is a potentially disastrous condition called hyponatremia , which can certainly ruin your race.


Because sweat/sodium losses are so individual, any generic guidelines on the replacement of sodium and fluid should always viewed with suspicion.

How much salt you lose in your sweat is genetically determined and doesn’t vary much at all, even given factors like diet and acclimation to a new environment. This means that, whilst you can only find it out by getting Sweat Tested, you only need to get tested once.

At Precision Hydration we have an exercise-free Advanced Sweat Test that tells you exactly how much you lose and creates a personalised hydration plan around that. We also offer a free online Sweat Test that helps you get started with personalising your hydration strategy through some good old fashioned trial and error in training. If you take that via the links in this blog, we’ll send you a free £10 voucher so you can try some of our multi-strength electrolyte supplements.


Your sweat only contains small amounts of potassium, calcium, and magnesium. It’s mostly made up of water and sodium. That’s why it tastes salty and you sometimes get those white, salty marks on your kit after a sweaty workout.

These other electrolytes do have a role to play but it’s sodium that’s crucial to staying properly hydrated and, because how much we lose in our sweat varies so wildly from athlete to athlete, it’s the electrolyte that needs more consideration than the others (unless you’ve got a specific deficiency in one of those).

So, if you’re looking for ways to improve your performance during the off-season, optimising your hydration strategy could be something to look at and I hope this helps.

Train hard,

Andy Blow has a degree in Sport and Exercise Science and was once the Team Sports Scientist for Benetton and Renault F1 teams. He founded Precision Hydration to help athletes solve their hydration issues. He also has a few top 10 Ironman and 70.3 finishes and an Xterra World Age Group title to his name.

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