Sweat loss during exercise

running form Jul 07, 2021
man running and experiencing sweat loss during exercise

Have you ever thought twice about how much you sweat during exercise? If you’re a sweater, have you considered how salty your sweat may be, how much you lose in a single training session and how this could affect your overall performance?  

These are some of the key topics I discussed with Andy Blow from Precision Hydration when we sat down together for an Innerunner Masterclass.

WATCH the full masterclass here

Staying hydrated during exercise

Sweat loss and hydration are key players when it comes to how you feel during exercise, as well as how fast you’ll recover after a long run, ride or swim. Yet, many athletes underestimate these critical factors. 

While sweating cools down your core body temperature and allows you to compete in endurance events throughout the year (and seasons), the downside of sweating too much is that you need to drink regularly to compensate for fluid loss.

But the consensus on what to drink, as well as how much you should be consuming during exercise is mixed. “In the 1960s, general advice was to avoid drinking anything during a race or long run, but this changed in the 80s, when the medical community began warning people of the dangers of dehydration and encouraging athletes to drink as much as 1.2L of water per hour – during an exercise session,” says Andy.

Drinking too much water before, during or after exercise can drastically dilute your blood sodium levels, which can cause a condition called hyponatremia. This is where your body pushes water into your cells instead of releasing it. Remember, sodium is an electrolyte that helps to regulate the amount of water in and around your cells.

If your blood sodium levels are too low, you may suffer from:  

  • Headaches
  • Loss of energy
  • Slurred speech
  • Confusion
  • Nausea and vomiting
  • Muscle weakness and cramps
  • Seizures
  • Coma

Extensive studies have shown that many athletes go through varying stages of hyponatremia – even before a race, as they believe they need to “load up” on water prior to an event to avoid dehydration.

Professor Tim Noakes, Founder of the Sports Science Institute in South Africa, has been trying to change this narrative with advice to stick to the middle ground and just “drink to thirst”. Noakes’s argument is that when you get thirsty, you should simply drink water and maintain normal hydration levels.

“This may be fine for those who don’t sweat a lot, but when you sweat, it’s not just water you lose, but key electrolytes too,” explains Andy. Electrolytes are charged ions – that perform all sorts of functions in the body for life and performance.

Some of the main electrolytes you lose in your sweat:

  • Sodium
  • chloride
  • Potassium
  • Calcium
  • Magnesium

The role of sodium in the body

One of the most important electrolytes is sodium. Interestingly, this is the same compound as table salt, which is why you may notice tiny white salt crystals on your skin if you sweat a lot. The body can’t replenish lost sodium on its own – it needs to be replaced through diet or supplementation.

Sodium plays a critical role in the body, particularly during exercise. It helps to:

  • Maintain the correct blood plasma volume – which assists performance
  • Transmit nerve transmission signals and impulses
  • Enhance muscle movement and contractions (without cramping).

Sodium supplementation during exercise

In a study published in the Scandinavian Journal of Medicine & Science in Sports, scientists from the Exercise Physiology Laboratory at UCJC analysed the effectiveness of salt capsules during a Half Ironman. In addition to rehydration drinks, a group of triathletes were given 12 salt capsules, divided into three doses during the competition, with the aim of replacing 71% of the sodium lost through sweat.

Their results were compared with athletes (of the same age, experience, and previous faster race times), who only drank water and rehydration drinks, therefore only replacing around 20% of lost sodium.

Those who took the salt capsules finished 26 minutes faster, on average, than those who only replaced 20% of the lost sodium. Researchers believe that the additional salt intake helped to improve the athlete’s salt/electrolyte balance, which directly enhanced their performance and allowed them to race at their peak.

How salty is your sweat?

While some need to replace lost fluid and salt more aggressively, others don’t – and can afford a more relaxed approach.

“Everyone loses a different amount of salt/sodium in their sweat, from as little as 200mg per litre of sweat, to as much as 2,000mg/l, which is largely genetically determined,” explains Andy.

“This means that the amount of sodium lost can vary up to 15 times between seemingly similar individuals. Therefore, a 'one-size-fits-all' approach (or standard electrolyte drink) may not always work when it comes to hydration.”

Should you take in more sodium?

One of the best ways to find out whether you should be paying more attention to your sodium levels is to take Precision Hydration’s free, personalised online sweat test. It’ll not only tell you what your sweat rate is, but also suggest what type of electrolyte you should be drinking before, during and after a race to maintain your hydration and sodium balance.

I offer Precision Hydration’s advanced sweat test at my practise in Laguna Beach. The test will help you determine your genetic sodium loss per litre of sweat. It takes around 30-40 minutes, and you don’t need to sweat or exercise during the test.

When considering your sweat/sodium loss, you should also consider:

  1. Your work rate - how hard or easy your training sessions are.
  2. Your workout duration – how much sweat you lose per hour of exercise, usually measured in ml.
  3. Your clothing – is it breathable and does it allow sweat to sit on your skin or evaporate?
  4. Your environment - Studies show that if you train in hot, humid conditions for prolonged periods, there’s a good chance you’ll need to replace lost fluids and supplement with sodium to prevent hyponatremia.
  5. Your genetics - Some people simply sweat more than others, which is why a personalised approach is key. If you start sweating a lot and performing poorly during an exercise session, or you crave salty foods after a long run or race, there’s a good chance you’ve lost a sufficient amount of sodium per litre of sweat.

Check out this blog from Precision Hydration to help you determine how much sodium you could be losing in your sweat.

Everyone is different

Whether you look at your sodium/fluid loss during exercise, your running form and technique or your breathing patterns, the bottom line is – everyone is different and it’s important not to compare yourself to others. Get to know your body and focus on your journey so that you can feel your best and avoid injury and/or illness when you train.













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