Why do we forget about hydration?

Uncategorized Dec 28, 2020

Why are electrolytes important for athletes? Why do athletes take salt tablets?

Difference between electrolytes and sodium:

Sodium is the main electrolyte that is lost in your sweat with fluids and plays a crucial role in maintaining your fluid balance. Often we use sodium and electrolytes interchangeably but it is sodium, in particular, we are talking about with regards to hydration status. 

It is true to say that sweat does contain other electrolytes such as potassium, calcium and magnesium that are involved in many processes but it is not crucial to replace these electrolytes during training and racing. Sodium is important as we all have individual sodium sweat rates so if you are losing a lot of sodium then you need to pay particular attention to losses and make a plan of how to replace them.

Why do we forget about hydration? 

Why is it that we stick to a plan with our training sessions for the day, planning out work, childcare and even who is cooking dinner; but often forget about something as simple as staying hydrated? 

It sounds simple, doesn’t it? However, it is very easy to get to the end of the day and not have drunk much more than a few cups of the good old Joe.  In fact, you may have already started the day on a back foot from the night before if you have not paid attention to rehydration after that late-night turbo session!

Remember the 3 Rs- Refuel, Rehydrate and Repair…..restock glycogen, take on fluids and possibly sodium (e.g electrolytes or salt tablets) and recover with protein and carbohydrates. 

How do we know we are dehydrated?

We have some very simple methods for determining dehydration. These are not fool-proof, but the simple Weight, Urine, Thirst points system is useful as a pitstop analysis; developed by the ministry of defence. 

  1. Measure your changes in weight before and after exercise to determine the % of weight loss for a particular exercise bout.  Studies suggest that we should always aim to avoid more than 2% loss of body mass due to dehydration, as this is the point at which aerobic endurance capacity on performance is negatively affected (1).
  2. By measuring body weight as soon as you get up; do you notice a drop in weight from normal?
  3. What about pee/Urine colour? Now the colour of pee can be affected by many things including certain medications, certain foods and being diluted by water in the toilet pan. Nevertheless, is the colour of pee very dark? 
  4. How Thirsty are you? Are you waking very thirsty?

The greater the number of “yes” responses the greater likelihood of you being dehydrated. Whilst useful, this is a little oversimplified and doesn’t give us the whole picture. It does however prompt us to start thinking a little more about hydration. 

It doesn’t mean however that simply “more is better”.  Over-drinking, especially without adding sodium (salt) or electrolytes is more likely to cause low sodium (salt) concentration in the blood (hyponatremia) which can cause just as many problems as dehydration itself.

Remember the 3 Rs- Refuel, Rehydrate and Repair…..restock glycogen, take on fluids and possibly sodium (e.g electrolytes or salt tablets) and recover with protein and carbohydrates. 

We need to be thinking about before, during and post-training.

How much fluid do we need and do we need extra sodium or different electrolytes?

Hydration is still poorly understood by some athletes and years on the fluid debate continues:  “drinking to thirst” vs “drinking to a plan”!

Whilst we would rarely encourage an athlete to match precisely the amount of fluid lost during training with their fluid intake whilst training (as there are other factors like glycogen depletion to consider), it is a good starting point for being aware how much is being lost and how much you may need to rehydrate with.

Why do we need to maintain hydration?

Simply put: as we become dehydrated this puts an extra psychological strain on our bodies with rising core temperatures, a reduction of plasma volume which increases heart rate and increased rate of perceived exertion (2).  

What can we do to stay hydrated or avoid dehydration?  

“Limit fluid losses during exercise to >2% of body weight” 

So what does this mean? Well, some studies (3) suggest that most athletes could consume between 0.4-0,8L per hour, but this is highly individual and needs to be practised, avoiding over-hydrating and hyponatremia. 

As previously mentioned, collecting this data at home will be an incredible place to start when it comes to getting proper hydration strategies implemented.  

The process is simple:

  1. Weigh-in before you train (with clothes or without), note the value on the spreadsheet
  2. Train for an hour
  3. If possible try not to pee in the hour of your session!
  4. Towel dry off
  5. Weigh in the same clothes / unclothed as before note the value on the spreadsheet
  6. Add to your original weight the weight of any fluids that you consumed and note this value down too!
  7. Calculate the difference between the weight pre-session + any liquid consumed during MINUS the figure at the end.
  8. The figure you have is the approximate amount of fluids you have lost - using 1kg= 1L approximately.

Why are electrolytes important for athletes?

Whilst collecting data across different activities in different environments helps us to understand how our bodies respond and how much fluid we lose, this only tells us half the story. What about the number of electrolytes you lose? 

We lose different electrolytes (potassium, calcium and magnesium), but the largest loss in sweat is sodium which helps us to retain fluid in the right spaces in our bodies. 

You could ask yourself a few simple questions about how much sodium (salt) is in your lost sweat. Sweat sodium losses vary hugely between individuals and are determined mainly by genetics. 

  1. Do you have white marks on your kit after training? (we don’t mean after a sea swim!)
  2. Does sweat make your eyes sting?
  3. Do you feel wiped out after training, unable to restore thirst? 
  4. Do you often feel a little “out of it” after or during long, hot training or races? 
  5. Do you crave salty foods after training?
  6. Do you get cramp regularly, especially in hot conditions? 

If you answer yes to many of the above you likely have salty sweat! The only way to really determine how much you lose and to personalise your fluid plan is to complete a simple sweat sodium test!  You can complete a Sweat Test at 4th Discipline, or if you’re in a different region have a look at the other Precision Hydration Sweat Test locations.  If you can’t make it to a testing centre fill in this simple questionnaire from the comfort of your own home.

Personalise your fluid plan

Once you have all your data you can really start to plan out how much fluid you should aim to drink in certain conditions at certain intensities and how much sodium you may need to be drinking; this may even include pre-loading and in recovery depending on the day.  (Following a sodium sweat test, you will find out how much sodium you lose and a suggested starting point to planning your sodium intake) Then it’s time to think about how this fluid plan fits into your fuelling plan! This is where it gets exciting! This part does take planning and comes back to the 3 Rs!  I will cover more details in a future topic. 

3 Rs- Refuel, Rehydrate, Repair 


  1. Sawka MN, Noakes TD. Does dehydration impair exercise per- formance? Med Sci Sports Exercise. 2007;39:1209–17
  2. Sawka MN, Coyle EF. Influence of body water and blood volume on thermoregulation and exercise performance in the heat. Exercise Sport Sci Rev. 1999;27:167–218. 
  3. Sawka et al 2007

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