Published on October 26th, 2017 | by adventuremag0
How salty is your sweat? (And what does that mean for performance?!)
By Cliff Harvey ND, Dip.Fit, PhD (c),
As an urban athlete, adventure racer, or raconteur-adventurer, you probably sweat…and you probably sweat A LOT.
And while the body is really good at regulating sodium (salt) levels in the body day-to-day, the whole situation changes when we start to sweat. Why? Because while the kidneys retain or excrete sodium to preserve sodium balance in the body, the concentration of sodium in sweat is fairly constant and differs markedly between individuals based on genetics. In other words, if you’re a ‘heavy sodium excretor’ you might lose a lot more sodium per litre of sweat than a ‘light excretor’, and so, when you’re active and sweating, this can lead to having either too much sodium or too little in the bloodstream, and this in turn can drastically reduce both mental and physical performance.
We all know how important it is to stay hydrated…
Becoming dehydrated will affect your performance faster than any other nutritional factor. And while there are plenty of experts saying that perhaps we’ve overdone it on the water lately (see Tim Noakes ‘Waterlogged’ for example), dehydration is still a known and real effector of performance.
Dehydration’s impact on heat regulation and various aspects of performance is measurable early in exercise, at a body weight loss of as little as 1% and as dehydration progresses, the effect on performance increases.1 A 5% loss of body weight in water can reduce work capacity by 30%, and a 2.5% bodyweight loss may reduce high-intensity work capacity by as much as 45%.
A study by Sawka and colleagues back in the 1980s graphically demonstrates this. They investigated the capacity of eight subjects to perform treadmill walking in very hot, dry conditions when they were hydrated or when dehydrated by a 3%, 5%, or 7% loss of body mass. All eight subjects could complete 140 minutes walking when adequately hydrated and 3% dehydrated. Seven subjects completed the walk when 5% dehydrated, but when dehydrated by 7%, six subjects stopped walking after an average of only 64 minutes. So, even for relatively low-intensity exercise, like walking or light tramping, dehydration clearly increases the risk of exhaustion and heat strain.
Average water loss is estimated at 2600ml per day. I have observed average water losses of approximately 100ml per hour with my athletes, which is roughly equivalent to this.
You’ll get a little from food (around 20% of your water requirement) and so a rough rule of thumb is to drink approximately 2.5 litres per day of water and take in anywhere between 100ml-1000ml for every hour of exercise (or more!). If you’re exercising for a long period of time or under extreme heat, it can be best to weigh yourself before and after training to help you estimate fluid losses.
So, we know that even small amounts of dehydration massively affect performance, and so, it’s imperative to regain the lost water weight between weigh-in and the event.
But many of us don’t know how much we need to ‘salt’
Many people don’t realise that they may have also lost large amounts of sodium in their sweat while they’re active. Conversely, some take high-dose sodium supplements even though they have lost little sodium
Sodium (salt) is a critical mineral in the body for the preservation of blood and cell volume and nerve conductivity. Human sweat contains sodium, along with other minerals in smaller amounts, including potassium, calcium and magnesium.
Blood sodium concentration during activity can be directly related to sodium intake.2 If you don’t replenish sodium properly, your performance could take a bit hit. Baker and colleagues have demonstrated that in athletes across various sports, there is at least a 43% difference between heavy and light sodium excretors3 while Lara and colleagues in a study of experienced runners, have shown a 250% increase in sodium sweat excretion for the highest versus lowest sodium excretors.4 That’s a big difference…and getting it wrong is not something you want to muck around with!
Sweat testing can tell you how much sodium you lose in sweat.
There are ways to measure the amount of sodium present in your sweat though. Based on technology used to measure sodium excretion in those with cystic fibrosis in a hospital setting, direct sodium testing is now available, under patent by UK-based company Precision Hydration (Nutrition Store Online and Elevate Coaching are the exclusive agents of this test in New Zealand). Baker (the scientist mentioned earlier) has suggested that sodium sweat testing is “a useful tool to estimate athletes’ sweat rates and sweat sodium loss to help guide fluid/electrolyte replacement strategies”.5
The great thing about the test is that it can be performed at rest so you don’t have to ‘work up a sweat’ in the lab, and you only need to do it once because sodium sweat levels are genetically predetermined.
And, once you know your level of sodium excretion, you can take the right supplement and replace the sodium that you’ve lost, to help you rehydrate effectively and to make sure you’re not sacrificing your performance.
- · Have a sodium sweat test performed to evaluate your sodium sweat excretion rate.
- · Take a low-sugar, sodium repletion product with sodium levels appropriate to your sodium sweat output.
H2Pro Hydrate by Precision Hydration
1. Murray B. Hydration and Physical Performance. Journal of the American College of Nutrition. 2007;26(sup5):542S-8S.
2. Hoffman MD, Stuempfle KJ. Sodium Supplementation and Exercise-Associated Hyponatremia during Prolonged Exercise. Medicine and science in sports and exercise. 2015;47(9):1781-7.
3. Baker LB, Barnes KA, Anderson ML, Passe DH, Stofan JR. Normative data for regional sweat sodium concentration and whole-body sweating rate in athletes. Journal of Sports Sciences. 2016;34(4):358-68.
4. Lara B, Gallo-Salazar C, Puente C, Areces F, Salinero JJ, Del Coso J. Interindividual variability in sweat electrolyte concentration in marathoners. Journal of the International Society of Sports Nutrition. 2016;13(1):31.
5. Baker LB. Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability. Sports Medicine. 2017;47(1):111-28.