I got my sweat tested – was it worth it?
If you didn’t know what you were in for heading into a turbo session, the programmers at Zwift let one of their infamous blue loading screens give you a hint.
“Turn your fan on now”
Sure, things are going to heat up, but this warning lulls the uninitiated into a false sense of sweaty security. A fan?! I don’t need a fan. No, I need an industrial size, wind-tunnel-like-power air conditioning unit. A towel wouldn’t go amiss either. Whilst there are no doubt exceptions, the sweat levels we cyclists achieve (particularly training indoors) is in a league of its own.
The importance of rehydrating and restoring electrolyte levels depleted through sweating is relatively common knowledge. It’s second nature to drop a tab, or scoop of electrolyte powder into your bottles before heading out, and many people consider their bases covered. However, compare one product to another and you will see sodium levels alone can vary from 250mg to 1000mg, not to mention the additional sources of magnesium or potassium. Although they are lost in smaller volumes to sodium, they still need to be rebalanced, and there are some electrolyte drinks that don’t include them at all! In addition to this, the composition and volume of sweat varies person to person, and will be largely affected by the external environment and intensity of the session.
Poor hydration (or rehydration), leading to electrolyte imbalance, takes its toll on your performance – you stand to suffer muscle cramps, impaired nerve signalling, and reduced transport of glucose, all decreasing your output.
Considering the number of variables at play, the approach each person needs to take is unique. Understanding exactly what those needs are and meeting them accordingly has the potential to hugely enhance your performance. So in the endless pursuit of marginal gains and science, I underwent a sweat test to see if it was worth getting such specific data on the perspiration problem.
What happens in a sweat test?
A spectrum of options fall under the umbrella term of a ‘sweat test’, from the physically demanding to the relatively passive. Luckily for me, mine swayed to the latter. After answering some basic questions about my overall health and fitness, two electrodes were attached to the inside of my forearm and a barely detectable current was passed through them in order to stimulate sweat production.
After around 10 minutes, the electrodes were replaced with a single collection disc. Inside the collection disc is a coil of fine tube, at the end of which is a blue dye to colour the sweat as it is taken up into the tube, without affecting its composition. Depending on the individual, I was told this could take anywhere from 15 minutes up to an hour to get a sufficient volume of sweat to run through the machine. For the first (and only) time, I counted myself lucky to be a naturally very sweaty person, and within 15 minutes we were ready to run the main part of the test.
Carefully extracting the tube coil from the collection disc, and in turn my sweat from the tube using a syringe, it was passed through a machine several times in order to evaluate its sodium content per litre.
What did I learn?
I can’t say the results were any grand surprise. I was deemed a ‘Low Salty Sweater’, which sounds more like an item of itchy knitwear than anything scientifically significant. Whilst I sweat a lot in volume, I never get white or yellow staining on my kit, nor salt crystals forming on my skin as I cool down – two of the main indicators of a higher sodium content. Per litre of sweat, I lose 614mg of sodium, so on the assessment scale I was presented with my result on the very far left, the opposite end being those who lose up to 2000mg of sodium per litre! What I wasn’t aware of was that the general composition of your sweat doesn’t change in any significant way after infancy, and is essentially genetically predetermined. So this value is near impossible to change, meaning you only need to ever do the test once.
Was it worth it?
Without the level of technology that was used in this test, there was no way (that I’m aware of) that I could easily establish the composition of my sweat at home. In this sense, the 614mg value that it provided me with is undeniably helpful. Yet I walked away feeling like I wanted and needed more information to make any kind of tangible change.
The onus is left on the individual to find out how much you actually sweat, which I was told was very easy to do at home. Simply weigh yourself before you exercise for an hour, and again afterwards, remembering to subtract the weight of any fluid you drank during the process. The result could be anything from 0.5l/h (low sweat volume) up to 3l/h (very high sweat volume) in the most intense conditions. Doing this, I learn I’m on the other end of the sweat spectrum, losing a massive 2 litres of sweat in 60 minutes spiralling into one of Watopia’s volcanos. I wasn’t asking for that towel under poetic licence.
Again, the data was easily collected, but ultimately doesn’t have as much value as it may seem. It’s representative of my sweat production on this particular effort, and naturally I will sweat more per hour trying to speed up Alp du Zwift than I do in one hour of a 5 hour endurance ride. Repeating it after different efforts would, at most, give me a rough ball park to aim for in terms of the electrolytes I add to my bottles going forward, but nothing precise. Better would be a device that would assess sweat rate and composition over an extended period of time, gathering more accurate data and providing a more precise picture of how the body sweats in different conditions.
As I briefly mentioned at the beginning, sodium isn’t the only electrolyte lost through sweat – magnesium, calcium and potassium are lost too, despite being in smaller concentrations, the impact that they have can still be significant. The test was only able to assess sodium, and when many electrolyte sources have just as varying levels of these other minerals, I feel it was somewhat lacking to omit them.
Given the data I received from the test, versus what I could roughly assess myself (the saltiness and volume), I wouldn’t necessarily consider it any significant gain to have the test done. A combination of common sense, trial and error and your bathroom scales, you could end up with a comparable or even better outcome.