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Sweat testing

Sweat testing measuring
Stu Bowers
14 Aug 2015

It may seem like nothing more than a byproduct but knowing the content of your sweat can improve your performance on the bike.

I can’t decide if I feel relieved or short-changed. Andy Blow, founder of Precision Hydration, is preparing me for today’s sweat analysis test and informs me it involves no physical exertion. Usually when Cyclist gets involved in a Lab Rat test, it ends up with us gasping for breath while slumped over a turbo trainer but, as Blow tells me, I can do this test sitting down in my jeans and t-shirt. 

‘But surely I need to be sweating?’ I ask, slightly baffled. ‘Don’t worry, you will,’ Blow insists with a smile, as he finishes setting up what looks like a lie detector in front of me. 

The easy option

Sweat testing pad

‘The test uses a process called iontophoresis,’ Blow says. ‘It’s basically a non-invasive way to get a chemical or a drug into your system, below the skin. At the most aggressive end of the spectrum is an injection, and the other end is a rub-on cream. This is somewhere in between and very effective, using a mild electrical current to deposit the chemical’s positively charged ions under the skin. The body’s response is that the sweat glands elicit a maximal sweating response. So directly under the pad you’re sweating as if you’re working as hard as you can in very hot conditions, without you even moving a muscle. Quite clever really.’

I can’t deny it sounds ingenious, although I’m still a bit disappointed I won’t be getting a workout. But Blow assures me this is the most effective method of collecting clean sweat samples without contamination, something that would prove very tricky during exercise. 

He cleans the surface of my skin with de-ionised water to remove residual deposits from previous sweating or any other contaminants. With the electrodes in position, all I have to do is sit tight for five minutes. Let the sweat-fest begin. 

Sweat testing collecting

The only thing I’m aware of is a slight tingling, a sensation like pins and needles. ‘Now for the clever part,’ says Blow, once the five minutes is up. He places a tiny disc directly over the spot where the positive electrode and chemical (pilocarpine) was located. Inside is a tiny coil of tubing that will draw up, via capillary action, a sample of my sweat. I watch it creep up the tube, appearing pale blue in colour due to a food dye used to make it more visible. 

‘And that’s pretty much it,’ says Blow moments later, as he verifies there’s now enough of my sweat in the tube to run the analysis. 

Your number’s up

The analyser measures the electrical conductivity of the sample, because electrolytes in sweat (mainly sodium) affect this significantly. The software then turns this into meaningful data.

‘We’re focusing on the sodium content,’ says Blow. ‘You have lots of electrolytes in your system, but in your blood in particular. Blood is where your sweat comes from and sodium is the predominant electrolyte. We apply a correction factor in the software to account for the presence of the other electrolytes. 10Mmol of sodium per litre of sweat would be really low; 100Mmol would be very high. The average we
see is around 40-45Mmol.’ 

Sweat testing

The whole point of the analysis is to help determine if a rider would benefit from taking on more or less electrolytes, based on how much they sweat and how salty their sweat is. Blow says, ‘There are people who sweat a high concentration of electrolytes but don’t sweat that much, so they may not have an immediate need to replace their losses, as they’ll be able to replace it through food. The high-risk group sweats lots and regularly (ie, they train a lot) with high sweat sodium content. That’s the triple whammy that can lead to issues, and it’s this group – which is around 20% of the 3,000 athletes in our database – that can benefit most from a more carefully considered electrolyte replacement strategy. Others can benefit too, but on a sliding scale depending on the variables. Generally the telltale signs are when the skin or clothing are caked in salt after exercise, muscle cramps, salt cravings and a general feeling of struggling in the heat.’

Blow also suggests people’s understanding of electrolyte replacement is often limited. An example of this is coconut water, which has recently been marketed as an ideal electrolyte replacement drink, but it contains very little sodium and a lot of potassium. So if you’re a high sodium sweater you could drink all the coconut water you like, but you won’t be replacing much of what you need. 

My sample shows a sodium content of 78Mmol – not super high, but definitely in the higher part of the scale. This equates to a sodium loss through sweat of 1,576mg sodium per litre. I’m well over the average which, combined with the fact I’m also a regular sweater, through frequent training and competing, puts me into the category Blow feels can benefit most from a more considered replacement strategy, or even some sodium pre-loading prior to hot events. 

Sweat testing machine

‘Training or competing in the heat, an athlete could easily expect to lose a litre of sweat per hour, and that’s conservative. Losses of up to three litres an hour have been seen in research,’ Blow says. ‘If the event time is also long then the sodium losses are potentially massive.’

I ask Blow if the high sodium content of sweat is potentially a knock-on effect from having a high salt content in your diet? ‘Concentration of sodium [in sweat] is predominantly genetically determined,’ he replies. ‘From our tests and experience with athletes it’s usually more the case that they have salt cravings as a result of high sodium losses, hence they add salt to food, not the other way around.’

So I should be considering a higher dose of sodium? ‘Your results certainly would point to that,’ Blow suggests. ‘If you were doing long rides in hot conditions you would be exposed to high risk and an inevitable effect on your performance. As you lose salt your blood volume drops, and therefore performance is compromised. Sodium replacement is not a performance enhancement – the best you can hope for is not to experience a performance drop-off. It boils down to trying to maintain your body’s homeostasis.’ 

Keeping tabs on salt

Sweat testing analysis

Most off-the-shelf electrolyte tablets deliver around 400-500mg of sodium, which is unlikely to be enough to replace my losses. Blow recommends I increase the sodium dose in my electrolyte drinks, but also warns me not to rely solely on the test numbers.

‘You have to be very careful not to completely outsource all the responsibility to science,’ he says. ‘It’s often considered as a “white knight” approach, claiming to have all the answers, but you still have to go out in the real world and find out if you see actual benefits. What we are trying to do is narrow down the playing field, but there’s still some trial and error. It’s a bit like a bike fit – you can apply the science but you still need to make sure this translates to the right level of performance out on the road.

‘The test enables us to prescribe a more suitable programme of electrolyte supplementation and help you achieve a greater understanding of how your personal hydration strategy works.’ 

For me, that means making some changes to my approach to exercise in the heat – and I certainly won’t be shying away from the salt mill next time I feel the urge to add a few shakes to my meal.

Contact: Precision Hydration

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