The importance (for fighters) of sweat testing and electrolyte replenishment when cutting weight

The importance (for fighters) of sweat testing and electrolyte replenishment when cutting weight

By Cliff "The King of the Cut" Harvey 

Fighters (and other athletes) routinely cut weight in the final days before an event to be able to compete at the ‘top end’ of their weight class and thus, have a relative weight advantage over their opponent. I guess it’s the old story…everybody gets tired…but big guys don’t get small!

Hell, I’ve done it, and I’ve helped hundreds of fighters to do it over the years too. And while extreme weight cuts (greater than 5% of bodyweight) could be considered excessive and possibly detrimental to performance (and health…) smaller cuts can be effective and safe…. if done correctly.

Two of the key considerations when recovering from a cut, before your fight, is you’re a) hydration status and b) your electrolyte (esp. sodium) status.

This is because the way we ‘cut’ is basically to sweat out a few extra kilos on the day of the weigh in.

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 people don’t realise that they may have also lost large amounts of sodium in their sweat and that this may not have been adequately replaced by the food you’re eating between weigh-in and fight.

Sodium (or salt) is a critical mineral in human physiology for the preservation of blood volume, cell to blood volume homeostasis and neuroelectric conductivity. Human sweat contains sodium, along with other minerals in smaller amounts, including potassium, calcium, and magnesium.

Blood sodium concentration in the short-term serum sodium concentration is directly related to sodium intake.1 If you don’t replenish sodium properly, your performance will take a hit…meaning that you may take a few more hits too!

Interestingly everyone has different sodium excretion rates in sweat. So, you might excrete a lot more than the next guy, and so, even if you aim to replenish sodium after a weight cut, you still may not get it right. For example, Baker and colleagues have demonstrated that in athletes (n=367) across various sports, there is at least a 43% difference between heavy and light sodium excretors2 while Lara and colleagues in a study of 157 experienced runners have shown a 250% increase in sodium sweat excretion between the highest and lowest sodium excretors.3 That’s a big difference…and getting it wrong is not something you want to muck around with!

Sweat testing

There are ways to measure the amount of sodium is 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 Precision Hydration. Nutrition Store Online are the exclusive agents of this test in New Zealand. Baker (the scientist mentioned earlier) has suggested that “sweat testing can be a useful tool to estimate athletes’ sweat rates and sweat sodium loss to help guide fluid/electrolyte replacement strategies”.4

The great thing about the test is that we can perform the test at-rest so you don’t have to ‘work up a sweat’ in our 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 on the mats, in the ring, or the cage, by coming in sodium-depleted.

Sign up for a sodium sweat test here



  1. 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.
  2. 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.
  3. 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.
  4. 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.



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