Endurance · 3 min read
Sweat testing for athletes is advertised under at least four names, and they do not all mean the same thing. Here is what each term refers to, and which one you probably want.
By Chris Gkoufas, DVOTION Labs ·
This measures volume: how much fluid you lose per hour. It is done gravimetrically — body mass before and after with drinks weighed — or with a wearable sensor that reports the rate as you work, or both.
What it answers is how much you need to think about drinking. What it cannot answer is what to put in the bottle.
These two terms mean the same thing: measuring what is in the sweat rather than how much of it there is. In practice that means sodium concentration, because sodium is the electrolyte lost in quantities large enough to matter over an endurance session.
A composition figure on its own has the mirror-image limitation. Knowing your sweat runs at 1,800 mg/L tells you nothing about how much sweat there will be.
Used properly, these are the umbrella terms — both measurements together, converted into something you can act on. That is what makes them the useful ones to search for, and it is what the assessment at DVOTION Labs covers.
It is worth checking, because the terms are used loosely. A provider advertising sweat testing may be measuring only one of the two. The question to ask is whether you leave with both a rate in litres per hour and a concentration in milligrams per litre. If you only get one, you have half the picture and no way to work out the other half from it.
Both, in one session, at an intensity representing something you actually do.
The reason is arithmetic. Sodium loss per hour is rate multiplied by concentration, and there is no way to derive either from the other — they are independent, and the combinations of the two are what produce genuinely different plans for two athletes who look similar on paper.
No, and the distinction matters. A sweat chloride test is a clinical diagnostic procedure used in the investigation of cystic fibrosis. Sweat testing in a performance context measures sweat rate and sodium concentration to inform hydration strategy, and is not a diagnostic test of any kind.
No. It helps, because prior threshold or heart-rate data makes choosing a representative intensity more precise, but the assessment stands on its own and the intensity can be set from your training data instead.
Around 60 to 90 minutes in total, of which up to an hour is the exercise itself.
The measurement is identical — rate and concentration are what they are regardless of who you are. What differs is the intensity it is taken at, which should represent something you actually do, and what the result is used for. Someone training for a hot marathon and someone doing an hour in a temperate gym get the same numbers and quite different plans from them.
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