Ep 15 - What is Sweat Testing and should you do one?

What is Sweat Testing and should you do one?

With so many bogus sweat testing places around, this episode is dedicated to explaining what sweat testing is and who it would be useful for.

I walk you through:

  • What’s involved in sweat testing
  • What’s being measured during a sweat test
  • Who Sweat Testing is best suited for
  • What to look for when doing a Sweat Test
  • What you actually do with the results

If you haven’t yet, make sure you go back and listen to Episode 14 with the sodium master Alan McCubbin for lots of nutrition gold when it comes to sodium and hydration for endurance athletes.

If you’re interested in understanding your personal hydration needs, book in for Sweat Testing with an Advanced Sports Dietitian today

Triathlon Nutrition Academy Podcast

Show Notes

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Episode Transcription

Ep 15 - What is Sweat Testing and should you do one?

00:04
Welcome to the Triathlon Nutrition Academy podcast, the show designed to serve you up evidence-based sports nutrition advice from the experts. Hi, I'm your host Taryn, Accredited Practicing Dietitian, Advanced Sports Dietitian, and founder of Dietitian Approved. Listen as I break down the latest evidence to give you practical, easy to digest strategies to train hard, recover faster and perform at your best. You have so much potential, and I want to help you unlock that with the power of nutrition. Let's get into it.

00:35
Welcome to the Triathlon Nutrition Academy podcast. Each week, we bring you evidence-based information to help you really nail the fourth leg of triathlon. No, it's not swim, bike, run, party. It's swim, bike, run nutrition!

00:36
So, I want you to put down that Google search and listen up as I help you unlock your true potential with the power of nutrition. If you haven't listened to last episode yet, I encourage you to go and do that. I chatted with Alan McCubbin, who's another Advanced Sports Dietitian, who I affectionately termed the "Sodium Master" because he has done so much work in this space.

00:58
And we talked about why sodium is even important in the first place. You know, why are there so many products that have extra sodium in them? Why are all the supplement companies trying to promote you to take and use more sodium? So where did that even come from in the first place? Are there any evidence-based guidelines to actually guide sodium replacement during exercise? What happens if we under or overdo our sodium replacement, among other things, and where does sweat testing fit into this whole picture. So, I would definitely encourage you to go back and listen to it if you haven't listened to it yet. It is nutrition gold!

01:54
Today, I wanted to explain to you what sweat testing is and whether it would be useful for you to do one or not. It is a service that I offer, to people in Brisbane. You must be around locally to do it, but lots of places do them. So, I'm going to actually give you some tips on what to look for to make sure you're not wasting your hard-earned cash on a bogus test.

What is sweat testing?

02:14
So, what we're trying to do is actually measure your sweat sodium concentration. So, we need to take a sample of your sweat while you're exercising to do that, and you know, measure what's in it. Plus, I always like to combine that with hydration testing. So, we're measuring how much sweat we're losing over a defined period of time as well. So, you can calculate your sodium loss, say per litre of sweat, along with how much sweat you're losing in mLs or litres per hour.

02:43
Now, the reason I only do sodium and sodium patches is because sodium is the main component of our sweat. We do lose small amounts of other electrolytes like potassium, calcium, magnesium, but very, very small amounts. And you can actually put patches on to test those things as well. But we don't really need to worry about them because we're never going to lose so much that it's going to be problematic.

03:06
In the lab, the gold standard for measuring sweat sodium concentration is a whole body wash down technique. And Alan explains that really well in our last episode if you want to go and listen to how that works. But that's only useful in a lab setting. And it's also only useful if you're on a stationary bike, it's difficult to do that on a treadmill running.

So in the field, we use sweat patches, and they're like a little band-aid that has a little cloth or material bit that actually collects the sweat sample. And then we wring that out and measure that. Now there are certain sites where you want to put the patch on, there's been a lot of research in the space of how to actually do sweat testing. So there's certain sites that we want to measure our sweat sodium, and then you can calculate from those sites with the right regression equations, we can actually calculate total body sodium based on what site was used.

03:55
So each site will measure your sweat sodium a little bit differently, we sweat differently at different sites, the rate of sweat is different, and also the sweat sodium concentration. So depending on where that patch gets put, you need to correct for total body sodium mathematically, to get what your total body sodium loss is.

04:14
In the field, I generally use two patches, you definitely need one, but I often do two as a backup. And I will often use both and get an average too. But in a research lab, where you’ve got unlimited resources and somebody's stationery and you don't have all the things in the field going on, then it can be common for people to put on five to sort of ten patches at different sites as well. But trying to do that in the field is just impossible. So typically just do two.

04:43
So what's involved when you sweat testing is you turn up you do a warm up and we put some patches on and then you go on exercise and then you come back we take them off and you analyse them. That's the simple version of what actually happens and there's so many things that you need to control for when we're doing sweat testing. So that's definitely the short, simple version. But there's a whole lot of science that goes into how to actually capture this information as accurately as possible.

05:11
And what we usually find is that individual's sweat sodium losses vary between sort of 20 millimoles/L to 60 millimoles/L. Now, there are outliers to that, obviously, but generally, your sweat sodium concentration will sit somewhere in there. And if it's outside of that, then it may be worth repeat testing, just to see if you did a test that wasn't particularly accurate for whatever reason.

05:40
What I really liked to do as part of sweat testing, which you should be doing is your hydration testing. Now I call it the same thing because I think that they go hand in hand. But hydration testing is where we're just trying to capture what your sweat rate is. So your sweat rate might vary anywhere between roughly 400ml/hour, up to 2.5-3L/hr. I've got a couple of guys that have done 3.5L/hour that’s their sweat rate, just insane amount of fluid coming out of your pores.

05:57
So the hydration components super important. We want to actually have an understanding of what your sweat rate is, and I think everyone should know that. Because you're going to sweat differently on the bike versus running. Generally, it's higher on the run because the intensity is higher. You also have evaporative cooling on the bike. So don't forget that. Even if it's still the air is still, you will still get some cooling by riding through the breeze. You also sweat differently in different environmental conditions.

06:46
So when you're doing sweat testing, you want to make sure that you're doing it in similar conditions to the event that you're lining up for. So you wouldn't do sweat testing in the height of summer for an event that is in the lows of winter. You want to try and replicate the environmental conditions of the race that you're doing the testing for. I like to do people's sweat testing, or at least just the hydration testing. So our sweat rate, I like to do that right across the season and the year so that you have an understanding of what your sweat rate is.

07:17
I think every athlete should understand that. And that's something I teach all of my clients how to do to actually go and do their own hydration testing themselves across different environmental conditions on the bike on the run, because you want to understand how much you sweat, because that's going to obviously help you know how much to drink during exercise, before exercise and after exercise to rehydrate. And your number is not always the same. It's always going to be different and will match the conditions.

07:50
I'm not going to get into the science of all the things that change your sweat rate. We might leave that for another episode. But there are a range of things that will actually affect what your sweat rate is your fitness, your genetics, a whole range of factors. So when you do a test that is not your answer your numbers for sweat rates and sweat sodium forevermore, it is for those conditions. On that day, at that pace, you know that intensity, how fit you are. And things like your pre-test diet also come into play there too. So there's a range of things that you want to control for and that will give you the most accurate results.


20:06
Let me know if this sounds like you. Do you feel exhausted by the end of the training week? Do you crave sweets in the afternoon and feel like you need a nap? Training for three disciplines can be absolutely exhausting if you haven't dialled in your nutrition. It can be frustrating when you can't quite piece together the solid race performance you know you're capable of and confusing when there's so much information out there. But you're not sure what's the right method for you.

My goal for you is to unlock your true potential and feel like a supercharged triathlete, firing on all cylinders full of energy and not only smashing quality training sessions, performing in every race too. If you're finally ready to start nailing your nutrition, join a powerful community of like-minded athletes in the Triathlon Nutrition Academy Program. Head to dietitianapproved.com/academy to check it out now. For less than the cost of a coffee a day, you will finally have a plan for your nutrition instead of winging it and hoping for the best.


Who is sweat testing best suited for?

09:30
So when it comes to sweat testing, who is it actually for? Who needs to go and do sweat testing? If you listen to last week's episode with Alan, you'll know that he's done some mathematical modelling to try and figure some of this stuff out. And his research shows that events sort of 10 hours or more, it's definitely important to have an understanding of what your sweat sodium concentration is and what your sweat rate is.

09:54
So if you're doing things like Ironman or ultra-marathons or 24-hour mountain bike events or anything that's sort of 10 plus hours, that's when it becomes important to really understand what your sweat sodium concentration is for that event. So trying to match the environmental conditions for that event. If you're doing something like a 24-hour event, and you're riding overnight, then you want to try and do some testing in cooler weather, to have a sense of what that might look like. And then doing some testing in the hot of the day around mid-day, so that you have a sense of scale of what your hydration plan needs to be across a 24-hour period.

10:31
You would do sweat testing for shorter events if you're having issues with something. So whether that's dehydration and the implications of that. It may not necessarily mean that you need sweat sodium concentration results, but you probably need to understand what your hydration needs are. If you've ever suffered from hyponatremia. So low sodium and it can be fatal. Or if you're somebody that vomits, has nausea, gets bloated, has issues with hydration and nutrition and exercising, or you're collapsing in events as well. If you're having issues, then it's just one of the pieces of the puzzle that you might need to investigate to figure out what's actually going on.

11:11
Now, like I said earlier, I think every athlete should understand what their sweat rate is. So every athlete should be able to do the hydration component of testing, to understand what's going on for them. It's something I teach all of my clients how to do, I set them up with Pro-forma to go and do some testing all the time and repeat it. And it's something I teach the Triathlon Nutrition Academy peeps to do as well, because I think it's so important. You need to understand what you're sweating like when you're exercising, whether it's a triathlon or a ride or run, and that's going to help you know what you need to carry, for one, you want to have the availability of the right amount of fluids for you.

11:55Also, what sort of gut training you need to do to be able to absorb the fluid that you're throwing at it so that you're not sloshing around in the tummy. And then, at the end of exercising, know how much you've lost roughly, to then work on rehydrating again to go hard for your next session. Because we know that dehydration affects performance. And the number that gets bandied around in the research is 2% body weight. But that's assuming that you turned up hydrated in the first place.

12:25
The number of people that come to sweat testing already dehydrated is mind boggling. So the 2% bodyweight rule is if you are turning up hydrated to start with, if you're already dehydrated, then it's no longer 2%. It's less than that. And there's thoughts around that percentage being a bit different for our longer events as well. So you might be able to weather maybe 3% to 4% dehydration for our longer endurance events, without it affecting performance negatively.

12:56
What to look for when you're doing a test?

This is really important because there is a whole heap of bogus testing out there, which is quite frustrating. And I really don't want you to waste your money doing tests. Because you'll get a number, whether that's accurate or not, is another story. So something you need to make sure of if you're trying to do sweat testing to understand your hydration needs for certain events, is that you do it outside in environmental conditions that are likely to match your race conditions.

13:25
We do sweat differently indoors compared to outside. So a lot of the research is done in the lab. And that's fine. They control the lab at a certain temperature and humidity. And that's what their data is reported on in in the results section like this is the sweat rates, sweat sodium concentration at this temperature and at this humidity. But for you, if you're trying to work out what you need for racing, then you should really do it outside to reflect race conditions, because you have got that evaporative cooling on the bike. And you might have a bit more evaporative cooling on the run as well depending on how fast you're going. But in the lab, they're going to sit you there with a fan in front of you. So that doesn't really represent what race conditions actually are.

14:05
The other thing you want to make sure of is you actually exercise while you're wearing a sweat patch. You're not just sitting there still. Now I've seen a few of these around. And Alan talked about them last week. It's putting a particular substance on your skin to drive sweat production. And I don't think there's any research in this space validating that for sweat testing in exercise situations. So just be mindful of patches like that. I don't know if there's any research studies to validate that as a technique. And to be honest, it's unlikely to actually reflect what your sweat sodium concentration is during exercise. You don't have your blood pumping; you haven't got your heart rate up. You don't have the evaporative cooling. There's a lot of factors in that that blow my mind about well one how it even happened in the exercise scenario when it's designed for cystic fibrosis.

14:58
So just be mindful of that, I've seen that lately. You also want to check that the practitioner that you're doing it with, it doesn't have to be an Advanced Sports Dietitian, it could be a physiologist, but you want to check that you're doing it with a qualified practitioner that is across the research around how to do it accurately. Because there are so many things that you can muck up when you're doing testing. It stresses me out doing sweat testing, because there are so many variables you need to control for to give you an accurate result. There's no point doing it if we're not going to get good data and I'm a stickler for doing things, right. So make sure you're doing it with somebody that knows what they're doing and please don't do a patch test that you've been sent in the post to do it yourself at home.

15:43
A lot of these exist, it's basically just money-making. There are so many things you need to control for to get an accurate sweat testing result. And you're unlikely to know all those things. And so you're more likely to F it up, I've been sent a number of reports from clients or people that have come to see me to actually get that data analysed. And to be honest, I kind of just say to them, Look, I don't know if that number is even right in the first place. So you're better off just repeating it. So save yourself the coin and actually do it with a qualified practitioner to start with.

16:11
And the most important thing to consider when you are doing a sweat test is that you actually get some application of that data for you in your situation, because a lot of places will just send you the number. Here's your sweat sodium concentration, here's your sweat rate. What is most important about doing the testing is how to then apply that to you and your situation or your event.

16:42
Do we need to replace all of it? Probably not. How much fluid do we need to drink to keep pace with our sweat loss, all of those things really need to be looked at by somebody that knows what they're doing to then apply that for you for it to be useful. Otherwise, it's just a number.

16:57
If you are interested in doing sweat testing, head to www.dietitianapproved.com/sweattesting, to register your interest or to book in for a test. And depending on where you are, there are probably other qualified practitioners around who can help you locally as well. I have had a couple of people fly in for sweat testing.

17:16
So there's that option if you are in Australia and want to fly for a sweat test, but there may be somewhere locally that can do a good quality sweat test for you as well. So definitely head to that webpage, if you are interested in doing it and you are a Brisbane local, otherwise send me a message and I can try and direct you around where to go in your area.

17:25
So I hope that's helped clear up a little bit of confusion around what testing actually is. I haven't gone into the details of how to do it accurately because there's no time for that. But just make sure that if you are interested in doing sweat testing, because you're doing endurance events, or you're having issues, that you find somewhere that does a good quality test, and gives you accurate results, because a lot of the testing will give you a number and whether that's accurate or not, we don't really know.

17:36
And then the most important thing is how to apply that information to you. There's no point just getting a number if you don't know then how to use it. I would look at starting to do your first test in the height of summer when it's nice and hot, because that's when your sweat rate is likely to be the highest. And I'd probably also start testing with the run too rather than cycling if you're a triathlete because your sweat rate is likely to be higher running than it is on the bike and then work backwards and do some really hot bike sweat testing so that you understand how to set your hydration up on the bike.

18:37
Say particularly for an Ironman, you want to be able to carry what you need and have a rough guide around how much you need to be drinking so that by the time you get to the run, you're not dehydrated, because you will have more success in an Ironman or a longer course event if you turn up to that run leg in the best possible state that you can.

So I hope that's helped. Send me a message if you need some more information about sweat testing or go to www.dietitianapproved.com/sweattesting if you want to have a look at the dates that we've got coming up on the calendar or send me a message if you need some direction with who to see in your local area as well. 


19:13
Thanks for joining me for this episode of the Triathlon Nutrition Academy podcast. I would love to hear from you. If you have any questions or want to share with me what you've learned. Email me at [email protected] You could also spread the word by leaving me a review and taking a screenshot of you listening to the show. Don't forget to tag me on social media at @dietitian.approved so I can give you a shout out too. If you want to learn more about what we do, head to dietitianapproved.com. And if you want to learn more about the Triathlon Nutrition Academy program, head to www.dietitianapproved.com/academy. Thanks for joining me and I look forward to helping you smash it in the fourth leg - nutrition!

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