I’m three months away from racing at the Ironman World Championships in Kona for the first time. My training is going great – but hydration has always been the limiting factor in my 140.6 races. Knowing that Kona is famous for the heat and humidity that destroys athletes, I’m ready to get serious about my racing hydration strategy. Lionel Sanders destroying himself in Coeur d'Alene, was another reminder that hydration is the difference between a decent finish and a DNF. So, to start my hydration journey, I needed a sweat sodium test.

Sweat Testing: Running on a treadmill collecting sweat

CAPTION: Sweat Testing: running on the treadmill collecting sweat from my forearm to figure out my sweat's sodium content.

Why is knowing about your sweat important?

Severe dehydration can kill you – and moderate dehydration can kill your performance in an endurance race. Not drinking enough in endurance sports – or drinking the wrong types of fluids – can bring your performance to a grinding halt. One key to sustained endurance performance is restoring your hydration through water and electrolytes – mostly sodium. If you know how much you sweat and how salty that sweat is, then you can tailor your drink so that is most efficient at replacing what is lost.

What is Sweat Testing?

There are several types of sweat tests, and two results you’re looking to find: how much do I sweat, and how much sodium is in my sweat. Sweat rate testing tells how much I sweat, and sodium content testing tells how much sodium is in my sweat.

Sweat rate testing

Figuring out how much you sweat (or your sweat rate) is an easy at-home project. You weigh yourself, work out, wipe yourself down, and then weigh yourself again. Your change in weight is how much sweat you lost. Of course, you’ll want to dive into the full protocol, and control for conditions similar to your race, but it’s an easy do-it-yourself test you can repeat for free. Here’s a great protocol from Runner’s World (there’s lots of similar protocols online). Be sure to test both bike and run. Swim is harder since we often accidently swallow water.

Sweat sodium content

Sodium content is different – you can’t do it without special equipment. The goal of sodium content testing is to determine the concentration of sodium in your sweat (how salty your sweat is). This is important because you need to replenish sodium to rehydrate. Without enough sodium, the water you drink won’t make it back into your blood – and you’ll stay dehydrated despite drinking water. Also, different from a sweat rate test, your sweat’s sodium concentration doesn’t change much – so you don’t need to retest often.

Once you know how much you sweat AND the amount of sodium in your sweat, you can then build a personalized hydration plan that should help decrease dehydration over long races.

What sodium sweat tests are widely available?

I’m an amateur athlete living in Atlanta, so I had to find a sweat test option that was publicly available (no support staff of doctors for me). I found three options, each with their own merits.

  • Gatorade Sweat Patches – currently selling online at two patches for $25, this seemed like a great option. In talking with a couple friends who had tried it, though, they had not had great success in using it. One hydration expert I spoke with at Precision Hydration recommended using them 6+ times to see if they produced similar results. Here’s an excellent article from Precision Hydration on the patches.
  • Elemental Altitude Sweat Test with a Horiba device – the Horiba device analyzes sweat and gives a sodium concentration. This is the option I chose, so all the details of this test are below. It requires that I run on a treadmill and produce a decent amount of sweat through working out, and retails for $100 (although discount information is below).
  • Precision Hydration Sweat Test with a Wescor device – Precision Hydration uses a device from Wescor that doesn’t require any physical exercise. You just sit there, put the device on your arm, and then it stimulates sweat and gives a sodium content reading. This is the easiest option, but also the most expensive at $150, and it is only offered at select Precision Hydration locations. The closest options to Atlanta as of Summer 2021 are 5+ hours away: Hilton Head, Memphis, or Orlando.

At first, I was concerned that Precision Hydration’s test might be more accurate than the Horiba machine. However, this 2013 peer-reviewed research article found that the results from the two machines were highly correlated. That tells me that for a race hydration plan – the cheaper test is just as good, although it just requires a little exercise.  Also, I really didn’t want a 10-hour round-trip drive if a similar test was available in Atlanta.

My experience sweat sodium testing

I was excited when I learned that sweat testing was available in Atlanta from Elemental Altitude in Dunwoody (right next to / inside of all3sports). When I emailed to book an appointment, I was told to bring running clothes to change into and to shave the insides of my arms. The shaving of the arms just helps with taking the patch off – eliminating the pain from removing a big band aid.

I arrived at Elemental Altitude, changed my clothes in the bathroom, and talked through the test with the guy who was giving me the test, Chuck. He explained that he would put a patch on each of my forearms, I’d run for a while on the treadmill. Afterward, we would squeeze out the sweat, and then measure its sodium content.

Chuck put on gloves, cleaned my forearms, and put on two big clear band-aid-like patches. Next, I was on the treadmill warming up.

One of the forearm sweat patches

CAPTION: One of the forearm patches, full of sweat and ready to be removed.

Now – here’s the one learning I’d share. The goal is to collect sweat – you don’t need to run at race pace effort. The race pace effort matters for sweat rate testing – where you’re going to wipe yourself down and calculate sweat rate. For the sodium testing, however, you’re just trying to collect a decent amount of sweat. My race pace running was unnecessary. I warmed up for about 10 minutes and then ran at race pace for 10 minutes. I could have run at a much easier pace – still sweating – and maybe run 5 more minutes. So, my suggestion for when you test is to be ok with an easier pace.

After running for around 20 minutes (and splashing sweat everywhere – I’m a heavy sweater), Chuck told me that was good, and I stopped. With gloves on again, he used some tongs to remove the two bandages from my arms. He then put each one into its own syringe and squeezed out a good tablespoon of sweat from each. That was somewhat nasty –like wringing out your shirt after a workout – yuck!

With the two sweat samples now in closed containers, Chuck got out the Horiba sodium concentration testing machine. He then calibrated it with two known concentrations (200mg of Sodium and 2000mg of sodium). That was cool to see. It took a few seconds, but soon the machine registered the 200 and 2000 numbers. Chuck cleaned the machine each time, and then once more before my samples.

Calibrating the sweat testing machine

CAPTION: Calibrating the machine, with my two sweat samples ready to be tested

My first sample registered 1100mg. My second, 1200mg. Chuck said that’s normal to have slight discrepancies, and that I could use 1150mg (per liter of sweat) in calculations. I’d want to restore about 60-70% of my sodium while racing, so each liter of fluid I consume should have around 800mg of sodium (1150 x 70% = 805 mg).

Chuck walked me through some hydration strategy ideas, and even suggested a few products to check out (SlayRX, Precision Hydration, and a few others). He also sent a follow up email with my result, a spreadsheet to use in planning, and answers to a few other questions I had.

After the test, I grabbed my towel that I’d brought, wiped down, and headed back to my car. It’s important to know that the facility does not have a shower, so plan on returning to your car sweaty.

How I'm changing my hydration (and nutrition) based on the results

Knowing my sweat’s sodium content is empowering to create a race-day hydration strategy. I know that for every liter of sweat I lose, I’m also losing around 1150mg of sodium. More importantly, I want to replace about 800mg of sodium in each liter of fluid that I drink. Over the next few weeks, I’ll test my sweat loss rate in at home several times in conditions like Kona (one benefit of Atlanta’s lovely heat and humidity).

Sample 1: Registering 1100mbg per 1 liter

CAPTION: Sample #1, registering 1100mg per 1 liter

Here’s what’s going through my mind now about creating a hydration plan. In the past I have sweated at the rate of about 1 liter per hour – so let’s say I get the same the results in my sweat rate tests. Now I know Gatorade Endurance, which is served on-course at many Ironman events, contains sodium at a concentration of 860mg per liter. That means that if I drank one liter of Gatorade Endurance each hour, I’d be close to my 800mg target. But if I sip water, I’ll want some extra sodium – either through salt tablets, drink additives, or sodium from my nutrition.

Sodium can come through food race nutrition as well. I’m a big fan of the Clif gel bloks - and the salted watermelon and margarita flavors both have a good amount of sodium per serving (100mg and 150mg, respectively, per 3 bloks). So, a liter of straight water and 5 servings of margarita Clif Bloks would get me close to the sodium I need – but would come with a hefty price of 500 calories per hour—too many.

So there’s still decisions and planning to make, but you can see that I’m trying to optimize for three numbers: 1 liter of fluid per hour, 800mg of sodium per hour, and a calorie goal (60-90 grams of carbs, or around 300-400 calories per hour). Prior to this test, I didn’t have that sodium number, and my performance has been impacted because of that. With all three numbers, it’s now just a matter of race-day logistics and practicing with my products of choice.

How can you get your sweat sodium content tested in Atlanta?

If you’d like to get your sweat sodium content tested like I did, you can email Elemental Altitude at info@elementalaltitude.com and ask to schedule your sweat test. If you tell them you heard about this test from me (Alex Fuller), then they’ll do the sweat test for $50 – an awesome deal for friends of all3sports. They also offer an at-home mail-in option. You take the samples yourself (it’s a straightforward procedure) and mail them in.

Elemental Altitudes also offers in-person FTP tests, as well as lactate threshold testing (blood test). I’m planning on doing a lactate threshold test soon, so be on the lookout for that article when I’m done.

Good luck testing – and may your hydration strategy help you achieve your personal best performance in your race!

After testing picture - sweaty

CAPTION: I was a happy, sweaty mess in the car afterwards - ready to plan my race day hydration and nutrition.


Article written by Alex Fuller.

Alex Fuller is the co-captain of the all3sports and Podium multisport triathlon teams. Based North of Atlanta, Alex has three young kids and does marketing full-time at UPS. Find him on Instagram @alexfullertri.

Alex Fuller - Team Captain



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