Sweat Testing – Sodium Loss
In this two-part blog, Coach Jon Reilly investigates sweat testing: what is it, how does it work and do you need to do it? The first part looks at fluid loss, and the second one at sodium loss. Let’s find out more.
Read the first article to find out more about fluid loss.
Sweat sodium concentration testing
To calculate your sweat sodium concentration, we want to know how many milligrams of sodium are being lost per litre of sweat. Like sweat rate, sweat sodium concentration varies wildly from person to person. Some lose less than 200mg of sodium per litre of sweat, whereas others lose over 2000mg. Data from Precision Fuel and Hydration suggests the average athlete loses around 950mg of sodium per litre of sweat.
Unlike sweat rate, sweat sodium concentration changes very little with varying conditions; some studies suggest it is mainly genetic and doesn’t change much once you reach adulthood. Repeat testing shouldn’t typically be needed. However, some studies indicate that sweat sodium concentration increases as exercise intensity increases. It can fluctuate slightly with changes in the amount of sodium in your diet and thorough heat acclimatisation protocols.
It is possible to get an accurate estimate of your sweat sodium concentration with a non-exercise based sweat test. Precision Fuel and Hydration provide an easy and affordable testing option with instant, accurate results. They use a process called iontophoresis to elicit a maximal sweating response under a pad placed on your arm. Under the pad, your body will produce sweat as if you’re exercising hard in hot conditions, without any effort at all!
If you cannot partake in the non-exercise based test, it is possible to come up with a good estimation yourself by gauging your experiences of the following, do you often?:
Find a build-up of salt crystals on clothing and equipment
Find that sweat that gets into your eyes or cuts stings
Commonly gets head rushes after standing up quickly after exercising
Often experience muscle cramps during exercise
Feel ‘rubbish’ after doing exercises in the heat.
Crave salty foods after exercising in the heat
The more of these indicators you’ve experienced above, the more likely you are to be on the saltier end of the sodium concentration of sweat; Precision Fuel and Hydration have a free questionnaire based on the above that can help you develop your estimate further.
Do you need to test your sweat?
As we have seen, there are huge differences between the sweat characteristics of individuals. Everyone will have different hydration and electrolyte levels requirements on race day.
If you have suffered poor performance in an endurance event, it could be down to many factors. Still, as we have seen, endurance performance can be severely hampered by inadequate hydration once you start sweating. If you’ve not got a handle on how your body sweats in different conditions, it could be your hydration planning that is holding you back. If you have an endurance event coming up in a hot or humid climate, it may help to test your sweat.
What to do with the information
Now we know your sweat rate in different conditions and your sweat sodium concentration. We can combine the two to estimate the total amount of fluid and sodium you are likely to lose in your sweat per hour in different conditions. But what do we do with this information?
We can use this information to develop ‘ballpark’ figures for a hydration plan. If, after testing, you realise that you have a low sweat rate (sweating less than 1 litre per hour), you may well be able to simply ‘drink to thirst’ in your events, with lower strength electrolyte drinks. However, if you have a very high sweat rate (more than 2L/hr) and discover you have a high sweat sodium concentration (over 1000mg/litre), then with these figures, you will be losing around 2g of sodium an hour. Over a 15 hour IRONMAN, that would mean losing around 30 litres of fluid and approximately 30g of salt! (This is an extreme example).
For those on the higher end, the next question is, ‘how am I going to replace all that fluid and salt in my race’, quite simply you are not. Trying to replace everything you lose is not the aim. It would be very uncomfortable and potentially dangerous. Athletes should be able to tolerate a certain amount of dehydration. Traditionally it was believed that losing more than 2% of body weight through dehydration was detrimental to performance. Now, faster marathon finishers have been found to finish a little more dehydrated, losing more bodyweight than those who are holding good hydration levels. It is now believed that the sweet spot of body weight loss during an endurance event is likely to be between 2-4% loss for most athletes. So, the sweat figures are there simply as a guide to how to approach your hydration. If you lose a lot of fluid and sodium, then you need to have an aggressive approach to hydration, preload with electrolytes and pro-actively hydrate early in an event with strong electrolyte drinks. Avoid drinking plain water; this will dilute the sodium levels in your blood even further, exacerbating performance degradation.
Like all things, getting hydration right is all about practice. The more you can hone your hydration in training, the more on top of it you will be on race day. Having said that, when it comes to race day, you don’t want to be too prescriptive with precise volumes of fluid and milligrams of sodium. Triathlon is such a dynamic sport; have the figures in the back of your mind, but don’t be afraid to adapt your plan on the fly.
If you want to find out more about sweat testing or are unsure what to do with the data after doing some testing, speak to one of our Tri Training Harder Coaches who can help you refine your hydration strategy even further.
Jon has been coaching with his local triathlon club in Hertfordshire around his full-time job as an airline pilot for several years. Unfortunately, Jon lost his pilot’s licence for 11 months in 2019 due to being diagnosed with testicular cancer (read his story here). He used the time off from flying to complete his Level 2 and Level 2 BTF diploma qualifications as well as a L3 Personal Trainer qualification. With his new coaching qualifications under his belt, Jon was able to join Tri Training Harder as a coach in 2019. He has now recovered from cancer, started flying again and is training hard for the coming triathlon season.
Jon has a flexible approach to coaching and training, from his own busy lifestyle he knows how to balance training around family, friends and social commitments. Jon loves to utilise the knowledge gained on his Personal Trainer course and finds incorporating well-structured strength and conditioning sessions vital to triathlon performance.
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