Some experts suggest to just drink water during exercise, we say “it depends”.

We have talked about hyponatremia before but to briefly remind you, it’s a condition that most often occurs in those who drink too much during exercise, as they struggle to excrete out the excess (your body slows down urine production when you’re active).

Hyponatremia is dangerous because, as more fluid enters the bloodstream, the body has to move some of it back out again to balance the sodium content. If the excess can’t be urinated out easily, fluid is forced into the intracellular space instead. This causes swelling of the cells. If this occurs in the brain it leads to headaches, confusion and even coma or, in extreme cases, death!

The advice we generally support is to largely drink to thirst during training and racing. Learn the signals that the human body has developed over millennia to tell you when you need to drink. Don’t listen to the latest marketing message that tells you to be drinking a fixed quantity every hour all day. We are all individuals and have individual needs. Learn to accommodate yours.

However, given the very nature of our business, we don’t think water alone will always provide you with everything you need to stay optimally hydrated while you are under stress and/or when you’re sweating a lot, as can happen frequently when you’re training and racing hard.

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A case-in-point is an article we came across recently from the British Medical Journal. It’s a discussion of a British Army infantry soldier who collapsed twice with symptoms of hyponatremia while on deployment, once in Saudi Arabia and again in Cyprus.

In short, the soldier presented with hyponatraemic heat exhaustion at the age of 24. They tested him using exactly the same protocol we use here at Precision Fuel & Hydration in our Advanced Sweat Test. His sodium loss rate was 81 mmol/l of sweat, that’s about 1658 mg sodium loss per litre of sweat. He was subsequently diagnosed with cystic fibrosis.

“Whoa!”, we hear you shout. That’s an extreme case and an extreme situation.

But is it?

After 4 years of sweat testing nobody has as much data on the athletic population as we do here at Precision Fuel & Hydration. We have conducted thousands of Advanced Sweat Tests on a wide variety of individuals.

What we know for a fact is that the soldier described in this document wasn’t a complete outlier, far from it. Our data shows that around 10% of all individuals we have tested to date have sodium loss rates ranked as “Very High”, right up there with this soldier. In fact, our most extreme sodium concentration measured to date was at 2300 mg sodium loss per litre of sweat. 

The really interesting thing is that many of the folks we’ve tested who turn out to have high levels of sodium loss in their sweat (or in some cases just really high sweat rates) seem to benefit dramatically from replacing larger quantities of it with the water they drink during exercise.

Additionally, our data indicates that the mean sodium concentration per litre of sweat is around 1000 mg, that’s about 2-3 times higher than the ‘hydration industry’ would have you believe when you look at the composition of most standard sports drinks.

We should point out at this stage that just because individuals present with high sodium loss rates does not automatically indicate they have cystic fibrosis — it’s more complex than that.

What it does indicate quite clearly is that for many athletes just drinking to thirst with water alone is not a sustainable strategy if you are trying to achieve breakthrough performances when sweat losses are high. Sodium balance is fundamentally important.

But what's your individual sweat sodium concentration? If you would like to find out then consider taking the Precision Fuel & Hydration Advanced Sweat Test.