Sweat testing

In previous blogs we’ve discussed what sodium is and how it might be helpful during exercise. We’ve also discussed that the amount of sodium lost in sweat varies significantly from person to person. In this article, we’ll take a look at how to determine your sweat sodium losses, and key considerations if you choose to do the testing.

Sweat testing methods

What is a sweat sodium test?

A sweat sodium test is basically a way of collecting a sample of sweat and then analysing it to determine the sodium concentration (how many mmol or mg per L of sweat). There are a few different testing methods, and this is important because some tests, or even the way the test was conducted, will influence how well the sample collected reflects the sweat losses that will happen in a real training or competition scenario.

Sweat testing methods

In the perfect world, a sweat test would collect sweat from the entire body, because sweat rates and sodium losses differ from one body region to another. The perfect test would also not interfere with the normal function of sweat glands, by not covering them or preventing the natural air flow to the skin. Whilst a whole body washdown technique exists that meets these criteria, it’s very impractical, requires exercise conditions that don’t reflect real world sports, and can only be done on a stationary bike.

Instead, the preferred method in recent times for use in athletes has been sweat patches, applied to specific sites on the skin. These patches absorb sweat as it’s produced. It can then be extracted from the patch either by using a large syringe to plunger it out, or a special tube that can be centrifuged in a lab. The sweat sample is then analysed for the sodium concentration using specialised laboratory equipment. More recently, a pocket sized electrolyte meter for sodium has been found to be a valid substitute, and can be used in field settings. The sweat sodium concentration is then combined with the sweat rate to determine the hourly sodium losses.

Biometric sensors for sweat testing

Recent advances in biometric sensors and wearable devices have led to the development of patches that can self-analyse the sweat they collect. This saves on careful patch removal, sweat extraction and analysis, reducing the need for skilled technicians and expensive laboratory equipment. Disposable versions of these p