How to Properly Hydrate Before Race Day

By Andy Blow | 4 Minute Read

For most athletes, pre-competition hydration routines tend to have one main goal, avoiding dehydration (remember we've addressed this topic in before when we discussed how much dehydration you can tolerate before your performance starts to suffer.)

This is understandable. Dehydration has been proven to hamper performance and sweat rates can easily exceed the body’s ability to absorb fluid, so starting an event ‘topped up’ makes logical sense.

However, avoiding dehydration should not be your only concern, there's a bigger picture to consider when optimising your pre-competition hydration strategy.


Human beings are not camels.


We cannot store up vast quantities of fluid for use later on. Once we're fully hydrated the body has to ditch any excess fluids. Many athletes believe peeing a lot is a good thing because we’ve all been told time and time again that producing clear urine in large quantities is a sign of ‘good hydration’.

As a result, many athletes just start drinking a lot more in the build up to an event. Ironically, this is most often the case with athletes who tend to suffer with hydration related issues during races. Those who struggle with cramps or headaches have more of a tendency to overcompensate, as they are conscious they must not become ‘dehydrated’. But, simply drinking more and more fluid pre race won’t solve any of those issues; in fact it could make them worse.

Pre-competition hydration is actually a bit of a balancing act. Having a better understanding of the science behind this will help you figure out a hydration strategy that works for you and gets you to the start line in good shape. So, let's dive in...

Glass of water 
Image by Steve Johnson via Stocksnap ©


Body Fluid Balance


Your body is roughly 65% water and this is mainly held in two places...

1. Nearly 2/3 of it is found inside your cells (intracellular fluid),

2. With the remaining third outside the cells (extracellular and interstitial fluid).

Of the extracellular fluid, roughly 20% (around 5 litres in the average adult) is in your blood. However, since you are a living, breathing, peeing, sweating, drinking, metabolically-active human being, your exact hydration level is in constant flux.

Your body does an amazing job of maintaining an optimal fluid balance by shifting fluid around internally, peeing out any excess, and by making you thirsty when you need to take more in.

This means that, in the days running up to your event, as long as you aren’t massively dehydrated to begin with or sweating excessively, all you need to do is to listen to your body and drink thirst. If you learn to read your body’s signals, you're unlikely to arrive on the start line significantly dehydrated. Take five minutes to read this blog, 'How to tell if you're dehydrated', if you have no idea what you are looking for.

Most of the issues over-drinking creates are related to the fact that body fluids are not just water but are a very salty mixture containing electrolytes.


The importance of electrolytes


Electrolytes are crucial for performing a host of bodily functions including cellular communication, nerve impulse transmission and muscle contraction. So their relative concentrations have to be regulated very tightly to allow them to do their jobs properly.

The main electrolyte found in extracellular fluid is sodium, which needs to be held at a concentration of around 135-145mmol/l in your bloodstream for everything to function optimally in the body. I've written more about why sodium is so crucial to athletes here.

Essentially, what happens if you drink too much is that you begin to dilute this critical level of sodium in the blood, potentially arriving at the start line depleted of electrolytes. In extreme cases this can lead into a dangerous condition called hyponatremia...


Avoiding Hyponatremia


You've probably already heard about hyponatremia. It's had a lot of press in recent years. The condition most often occurs in those who drink too much during exercise, as they struggle to pee out the excess (your body slows down urine production when you’re active).

Hyponatremia is dangerous because, as more fluid enters the bloodstream, the body has to move some of it back out again to balance the sodium content. If the excess can’t be urinated out easily, fluid is forced into the intracellular space instead. This causes swelling of the cells. If this occurs in the brain it leads to headaches, confusion and even coma or death!

If you haven't seen it already, we talk about the dangers of hyponatremia and how to avoid it in more detail here. In summary though, drinking to thirst is the best way of preventing hyponatremia. 

Precision Hydration cap
Image by Andy Blow (©)


How to Properly Hydrate Before Race Day


So, now you understand some of the science behind hydration and what can happen when things go wrong, let's talk about how to get things right...

1. Avoid over-drinking. Urine colour and thirst are the most helpful indicators of how hydrated you are.

If your pee is dark in colour and/ or low in volume, chances are you're somewhat dehydrated.

If it's crystal clear and you're in and out of the loo every 5 minutes, you're probably overdoing it.

2. Increase sodium intake in the last couple of days before the event.

The extra sodium will increase fluid uptake into the bloodstream, by helping to ensure sodium levels are not diluted. It'll also increase thirst causing you to naturally drink a little more.

You can increase sodium intake by adding electrolyte supplements to the water that you’re drinking or by putting additional salt on your food. Just bear in mind that most sports drinks are actually relatively low in sodium (at around 400-500mg/l) and that you generally need something stronger than that (around 1500mg/l) to actively pull more water into the bloodstream and keep it there effectively. 

If you're keen to get a bit geeky and dig a little more into the science of pre-loading with sodium then get the kettle on and dive into this blog I wrote about it.

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