Sep 6, 2022


  1. It helps transport calories across the stomach to the lower intestine, so it acts as a transporter & aids absorption.
  2. Maintains blood volume.


  1. Blood delivers oxygen to the muscles to create energy and offload waste (eg. Carbon Dioxide).
  2. Shunting blood to the skin to dissipate the heat we have generated through exercise (sweating).
  3. Blood goes to the gut to help with absorption.

During exercise as you get dehydrated the biproduct is we lose blood volume and this is where the body goes into competition for that blood because your muscles are calling out for oxygen, your skin is calling out for blood to dissipate the heat, and your gut it calling out for blood to help absorb the calories you are consuming.

Who Wins……….

The skin is the winner because we must get rid of the heat or there is a direct impact on your brain and organ function.  The higher the intensity of the workout, the more heat it will generate!  The muscles are second due to our motivation to keep exercising and finally the gut, so it becomes harder to absorb calories during exercise. So, when we get dehydrated and blood is going to the skin it increases our perceived effort for the same amount of work, we get a drop in economy, a drop in the absorption rate of the gut, and therefore a drop in performance.

Performance starts to decline after about 3-4% dehydration so this will be when you start to see a negative impact on your performance.


  • Heat & Humidity
  • Altitude
  • Individuality (Genetics, Fitness Level).

It’s important to note that you will be dehydrated by the end of a training session, we are not looking to retain hydration as it can be a risk of hyponatremia, but the mission is to not be too dehydrated.

So, if you are racing an Ironman, when you finish the bike you don’t want to be too dehydrated about 1% or so, so that when you start the run you are not too dehydrated so that you have more hydration to lose during the run rather than too dehydrated and lose performance.


The consequences of dehydration are plasma/blood volume dropping and becoming viscous (thick) and the heart then must pump harder, and this will cause you to experience performance decline, muscle weakness, and fatigue. 

Some signs and symptoms of dehydration are headache, confusion, and performance starting to drop off.  Then when hydration is more severe the signs can be dark urine and you stop sweating.


  • If less than 60mins then you can drink to thirst and plain water is fine.  **But women who are in their high hormone phase (the 2 weeks before your period) and post-menopause women, your thirst signal becomes dampened so you will need to set an alarm to remind you to sip fluid every 10-15mins and your hydration needs will change to a hydration product.**
  • Over 60mins it now becomes useful to aid your performance to use a hydration product (this is a solution that contains a small amount of sugar and salt, as sugar is the co-transporter for the sodium fluid to cross the intestinal barrier to keep that blood volume up), the amount you need is 10-12ml/kg of body weight/hour.

** For fluid to make its way into your bloodstream swiftly and efficiently it needs to be a lower osmolality than our blood.  If your blood is more concentrated than the fluid you drink, your small intestinal cells will let the fluid through the intestinal walls to add water to the bloodstream and lower the concentration levels, BUT if you take in fluid that is too concentrated, your intestinal cells will reverse course and pull water from the vascular spaces of your body to dilute the higher osmolality in your gut.  (Basically, water leaves the spaces where you want it and goes into your digestive system to dilute the fluid sitting in your gut.)  Which in the end leads to dehydrating yourself and triggering GI Stress. **

  • Over 75mins Hard Interval Sessions use a hydration product 10-12ml/kg of body weight/hour and sip frequently every 10-15mins.
  • Long endurance sessions use a hydration product starting early with the higher ratio of 12ml/kg of body weight/hour then taper down to the lower end of 10ml/kg of body weight/hour.

It is quite common to start your long endurance session not hydrating and get to an hour plus in and realise you have hardly drunk anything; this can lead to slipping over the 3% hydration and affect your performance.

  • For the sessions over an hour then calories will need to be consumed as well and these should be separate from your hydration.  The reason it is not a good idea to mix your calories with your hydration (like sports drinks) is that it makes the fluid highly concentrated, and it cannot be absorbed through the intestinal wall, yet.  So, your body has to redirect the fluid from the working muscle tissue to the small intestine and push the water across the intestine barrier to dilute this concentrated product so it can be diluted enough to get absorbed but meanwhile, you have pulled oxygen from the blood back towards your intestine and so will be problematic on your performance.

If you are going to use sports drinks for your nutrition, then remember this is separate from your hydration not a part of your hydration needs.


Sprint/Olympic again it’s 10-12ml/kg of body weight/hour sip regularly every 10-15mins.   Go towards the higher end if the weather is hot or course is particularly hilly or at altitude or if a female is in a high hormone phase.

Ironman/70.3 again same hydration amount but it becomes more of a focus to minimise loss so not going into the run less than 3%.  We will be absorbing less fluid on the run due to stress on the body like fatigue, it can be good to alternate between water down coke and water during the run as the sugars in coke are quick digesting, literally, as it hits your tongue, so if you have been suffering with GI Stress this could be a solution for you to get in some fuel.



Water supports your immune system and is critical for cellular health.  We need water to stay alive and maximise the performance of our bodies.  It contributes to recovery and helps the absorption of your daily calories.

It is important to restore your hydration daily as you are dehydrated when you finish your training sessions and rehydrating will facilitate recovery and get you ready for your performance in your next workout.

Signs that you are dehydrated in daily life are feeling tired in the afternoon, this can also show up as hunger and is when you can then reach for the sugary snack when actually you are dehydrated.  Alertness declines when dehydrated.   It is best to hydrate with sips throughout the day rather than guzzling a big glass of water in one go as this can cause a volume response – signalling your body to pee out more than you’ve taken in or GI stress.

Plain water does not have any transporters (sugar & sodium) and so unless you are drinking it with food can struggle for it to be absorbed and end up with the volume response mentioned earlier which can be the reason why you end up peeing a lot when just drinking plain water.  What you can do is add some maple syrup & salt (sea salt) to your water to give it those transporters.  The recipe is 1 teaspoon of maple syrup, a pinch of salt to 200ml of water (you shouldn’t be able to taste the salt or the maple syrup, it just tastes smooth), you can also add ginger to this if you like as well.

Other drinks that can help your daily hydration are tea, green tea, and coffee (be careful with caffeine as adenosine hormone builds up throughout the day to make you feel drowsy in the evening.  Caffeine is an adenosine decoy that floats through your bloodstream and binds to the adenosine receptors.  So now, instead of slowing down, your pituitary gland senses something is up and that you need energy and gives you a shot of adrenaline.  That’s fine early in the day but the half-life of caffeine is about 6hrs, so if you have a coffee at 3 pm you still have a shot of expresso effect kicking around at 9 pm and for some, it can be longer.  So, try avoiding caffeine from around 12/1 pm depending on what time you go to bed). 

So, there you have it, I hope you all now can see why being hydrated is important and start to implement it more in your daily lives as well as during your exercise and races.