Andy Blow, hydration expert and co-founder of Precision Fuel & Hydration, explains how to stay hydrated when you’re training and exercising in hot conditions.
At Precision Fuel & Hydration, we often get asked: how much should I drink?
Hydration can have a significant impact on an athlete’s performance, so understanding how to maintain your hydration levels before, during, and after exercise is crucial.
Proper hydration supports cardiovascular function, enables your body to dissipate heat created by your working muscles. In addition, it reduces fatigue; all helping your body work more efficiently.
When there are additional factors like heat to consider, you might need to adjust your hydration strategy. This is to account for your increased sweat losses…
Hydration is much more than just water
Before we look at how to stay hydrated, it’s important to understand that hydration is much more than just the amount of water we drink.
Your body is constantly aiming to maintain a balance between water and electrolytes. These are vital to many critical body functions.
It’s therefore important to drink enough fluid and sodium. This is to replace an adequate proportion of your sweat losses when exercising for sustained periods in hot conditions.
Your body wants to maintain homeostasis but drinking just plain water during long or particularly sweaty sessions can upset that balance as it dilutes the sodium concentration in your blood. So, your body’s solution to drinking too much plain water is to expel the excess water through urine. Therefore, it’s basically going to make you pee more.
Unfortunately, you’ll also pee out some of the electrolytes from your system. This further dilutes your blood sodium levels and impacts your performance (and wellbeing, in extreme cases).
That’s why it’s important to take on an appropriate amount of electrolytes – mainly sodium – alongside the water you drink. This ensures that more of that fluid is retained.
Sodium is the main electrolyte lost in your sweat. It plays a key role in how your body functions as it helps maintain fluid balance and cognitive function. For this reason, it’s important to replace the sodium you lose to some extent when your sweat losses really begin to mount up.
Impact of heat
Whether it’s training in the UK summer or travelling to a race abroad, the human body is simply unable to exercise as hard in the heat.
Athletes in the heat will commonly sweat between 1-2 litres per hour, but we’ve worked with athletes who lose more than this. For example, this includes a pro tennis player who sweated out 3 litres an hour in the heat!
Needless to say, it’s not possible (or advisable) to drink enough to replace 100% of your sweat losses. However, you’re aiming to drink enough to avoid losing more than ~% of your body weight by the end of a session.
There are tactics you can use to help optimise your approach to hydration in the heat…
Pre-hydrating
Consuming a strong electrolyte solution in the build-up to a race or training session will boost your sodium levels. As a result, it encourages your body to retain the water you drink, helping you to start fully hydrated.
The timings of a race day, particularly large events, can be vastly different to an athlete’s usual routine. This is why planning your hydration strategy is key in this scenario.
Athletes preparing for a hard session or race should drink ~500ml of a strong electrolyte drink the night before to encourage their body to retain fluid. This will boost blood volume.
On the morning of the session or race, it is recommended that athletes drink another bottle of strong electrolyte drink to top-up blood plasma volume. Ideally, this should be done 90 minutes before the start.
Aim to finish this drink 45 minutes before the event starts, to give the body time to process it.
Hydrating during exercise
For short sessions or races lasting less than ~90 minutes, drinking to thirst is likely to be adequate. You will lose fluid through sweating but can rehydrate afterwards to replace any fluid lost.
During sessions and events over 90 minutes, the need for fluids and electrolytes starts to become apparent for most people and the amount you will need to drink is largely driven by your sweat rate (i.e. how much fluid you sweat out). This can vary dramatically and will obviously be influenced by the heat you’re exercising in. Moreover, as you’d expect, you’ll want to drink more in hotter conditions.
When your body is working for more than two hours, it’s time to add sodium to the fluids you’re consuming.
During very long races, especially those in the heat, where total sweat losses can be significant over a period of many hours, personalised sodium supplementation starts to become important. This is especially true if you’re someone with a high sweat rate or high sweat sodium levels.
A one size fits all approach doesn’t work. Every athlete loses a different amount of sodium in their sweat, from as little as 200mg of sodium per litre to more than 2,000mg of sodium per litre. Moreover, how much you lose in your sweat is largely genetically determined, so it’s important to ensure that you’re using the correct strength of electrolyte to replace your own individual losses.
To personalise your intake, create a hydration plan according to your particular needs.
Hydrating after exercise
When your sweat losses have been fairly low and when you don’t need to perform again for a while, simply drinking and eating normally is usually enough to replace the fluids and electrolytes you lost.
However, when your sweat losses are high, or you have to restore fluid balance rapidly because you’re exercising again later that day, a more proactive approach to rehydration may be needed. This helps your body restore equilibrium in a short space of time.
The period following exercise is when the body is best placed to rebalance fluid and electrolyte levels.
Research shows if you want to rehydrate quickly in a situation where you have become quite dehydrated or need to be back on top form again very soon, then you should aim to drink about 1.5 times more fluid than you have lost. Additionally, you should include a strong sodium-based electrolyte in that drink to account for the salt loss too.
For more advice and information on fuelling and hydration, visit https://www.precisionhydration.com/performance-advice/
