I thought I had hydration sorted – drink water, with an electrolyte, and I was set.
But after trying a sweat test from experts at Precision Fuel and Hydration, I realised I’d been overlooking a key area: sodium loss.
The sweat test itself was straightforward. I didn’t have to exercise; instead, the team placed electrodes on my forearm to stimulate sweat.
There was a slight tingling sensation, and once the sweat started collecting in a tube, I could see it happening in real time, then the results came in quickly.
The main takeaway from a sweat test is your sweat sodium concentration. Essentially, how much sodium is in each litre of sweat you lose. Determining your sweat rate is done by weighing yourself before and after a session and noting the amount of fluid consumed, which is useful for race preparation.
Once you have your sodium concentration and sweat rate, you can develop a hydration plan to detail how much fluid to consume, the strength of electrolytes needed, and the sodium concentration to aim for to replace what you lose through sweat.
I went along to Pearson Performance, SW14 8AG but there are testing locations across the UK.
The sweat test – what to expect
The test is a simple and stress-free test that requires no exercise. It takes about 30 minutes and allows you to better understand what your sweat is made of.
Two small electrodes are placed onto the forearm, a little way apart, and secured against this skin.
The sweat inducer turns itself off when it is finished.
The electrodes are removed from the subject’s arm.
The area below the red electrode is wiped using some clean dry gauze.
The small sweat collector is placed on the spot where the red electrode was, and fastened securely with the strap.
You will see the sweat collecting because there is some blue dye in the tubing. It will take between 5 and 20 mins to fill from a third to a half of the tubing which is enough to run the test.
The tube is then connected to the analyser using a syringe.
The highest stable reading is then taken.
What did I learn from my sweat test?
The key number that you will get from the sweat test is your sweat sodium concentration; that is, how much sodium is contained per litre of sweat that you lose. Knowing this number provides the basis for designing your individual hydration strategy.
The other piece of the puzzle is to understand your sweat rate in litres per hour. This will be individual to you, and will change based on the environment you are exercising in; for example, a warmer environment will increase sweat rate.
Working out your sweat rate is relatively simple Taking a body weight measurement before and after a session and accounting for the amount of fluid consumed and the duration of the session will give you your sweat rate in litres per hour.
If planning for a race, the sweat rate estimates should ideally be made in sessions that include race-pace work and in similar temperatures that are expected on race day.
And that’s it! Once you have worked out your predicted sweat rate and your sweat sodium concentration you can begin to develop your hydration plan together with one of our sweat test experts.
This will include how much fluid to drink, what strength electrolytes to use, and importantly the relative sodium concentration that you are aiming for because this is what matches the losses via sweat.
You can speak to the sports science team to really dial in your fuelling and hydration plan leading into any upcoming races.
Book a test, starting from £99 here.