Sweat, Sodium, Electrolytes and Why Triathletes Should Care I talk to my bike…..it’s weird…...but much like Hockey Goalies talk to their posts, I like to give my bike a little encouragement and congratulations every now and then. We put in the effort together and the reward should be shared.

Now, if my bike could talk back, I’m almost 100% sure the first thing it would ask is: “Why are we always riding in the rain?” Needless to say, I sweat a lot.


Everyone sweats.  Sweating is a perfectly normal response by your body to help maintain a comfortable body temperature.  When you’re hot, you sweat to help cool your body down.  Some people sweat more than others and everyone’s sweat is different.

Not understanding your sweat can be detrimental to triathletes resulting in muscle cramping, fatigue, and the more serious dehydration and hyponatremia.

So, as the weather warms up it's important to not take your sweat for granted.

Ladies and Gentlemen, let’s talk sweat.

Sweat Rates

The first place to start is with your sweat rate - the amount of sweat you lose during an hour of exercise. Every pound of body weight that you lose during exercise is equivalent to about 16 oz of sweat (1000ml/kg). This is the key variable to understanding your Sweat Rate.

To figure out your SW, perform the following:

[(Pre-training weight (kg)) – (Post-training weight (kg))]*(1000ml) + (fluid consumed)/(training time)

Here is an example from a training session a few weeks back:

[82.5-81.9]*(1000ml) + 591ml / 1 hour =  1191ml (40.21oz)/hr

Your Sweat Rate is essential to ensuring you hydration strategies are not resulting in over or under hydration. Based on the above, I look to consume between 700-800ml/hr as replenishment. It is important to note that you don't need to replenish everything that is lost. Your body can handle some level of water loss and still preform at an optimal level, but it is important to replace some of those lost fluids.

Some tips when testing your SW:

  • Make sure you’re well hydrated prior to test
  • Towel off before post-training weigh-in
  • It goes without saying, but weigh yourself naked post & pre-test.
  • Take note of testing conditions – humidity, temperature, time of day, etc.
  • Test under different conditions for all three events to get an idea how your Sweat Rate changes.

What’s in your sweat and why it matters for Triathletes?

For short training session (under 60 minutes) fluid replenishment needs should be minimal to maintain high performance. Assuming you are well hydrated and fuelled, you should also be ok with just plain old water.  I use just water for anything under 60 minutes and have not issues, even as a big sweater.

As training sessions get longer and/or during events, the situation begins to change and you should start paying more attention to injecting more than just water, but also electrolytes.

The majority of your sweat is made up of water; however, your sweat also contains key electrolytes such as sodium and potassium, magnesium and calcium in smaller amounts. Each of these deserves their own article, but here is a quick snippet on why each is important


  • Sodium helps the body keep the right amount of water inside and outside your cells and in your blood. The amount of sodium in sweat varies individually between averaging 500mg sodium/lb sweat (but can range between 220 to 1,100 mg) If salt is not replenished, triathletes run the risk of developing hyponatremia, which canbe fatal. For salty sweaters I highly recommend The Math of salt loss.
  • Sodium levels vary greatly from person to person and are arguably the most important electrolyte to pay attention to. Salt tablets should be considered a must for triathletes, in my humble opinion.  I use NUUN Tablets for my sodium needs. Taste great and are easy to carry on bike and on runs.



  • Magnesium plays an important role in supporting chemical processes in the body including muscle contraction and relaxation and synthesis of proteins and fats. Deficits can lead to fatigue, reduced muscle twitches or cramps. It may also help in reducinglactic acid accumulation.


  • Calcium helps in the contraction of the heart muscle, is required in the process of muscle contraction and is needed to active the enzyme lipase which breaks down fat stores to produce energy.

So how much of these electrolytes are actually in our sweat? While I found varying numbers out there, common averages of the electrolyte content of human sweat are:

  • Sodium - 0.9 grams / litre
  • Potassium - 0.2 gram / litre
  • Calcium - 0.015 gram / litre
  • Magnesium - 0.0013 gram / litre

The concentration of the above nutrients differ widely, sodium has the most variability between individuals, which the remaining three being a little more consistent. Despite this, their replenishment over longer periods of time should not be ignored and are important to ensuring you are performing at your optimal level throughout the entire race.

Don’t Ignore Your Sweat!

It is hard to ignore and it shouldn’t be ignored! A few takeaways:

  • Calculate your SW for different events under different conditions
  • Pay attention to sodium, potassium, magnesium and calcium intake:
    • Develop a fluid replenishment plan that includes key electrolyte replenishment
    • Get your sweat tested if you want to get really specific
    • Take a multivitamin that contains key electrolytes
    • Use salt tablets/electrolyte mixes during longer training
    • Incorporate foods high in the respective minerals into your diet – bananas, potatoes, dark leafy greens, fish, and beans.

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