Surviving your training in a heatwave

Andy Blow, founder of leading sports fuelling and hydration company  Precision Fuel and Hydration, discusses how to stay hydrated and survive your training throughout the hotter months.

At Precision Fuel and 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 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, and 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 for maximum impact.

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, essential minerals (like sodium and potassium) that are vital to many critical body functions

It’s therefore important to take on the correct levels of both to properly hydrate; it’s the balance that’s key.

Drinking just water can upset that balance, diluting the body’s concentration of salt. Always wanting to maintain equilibrium, the body’s solution to this is to expel the excess water through urine. It’s basically going make you pee!

Unfortunately, this will also take with it some of the electrolytes in your system, further diluting your blood sodium levels and impacting your performance (and wellbeing, in extreme cases).

That’s why it’s important to take on an appropriate amount of water for you, but also electrolytes to make sure that water is retained.

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. For those with high sweat rates, they’ll be drinking less than they sweat and the result is dehydration.

Sweating with inadequate fluid replacement decreases plasma volume (which makes up about 55% of the body’s total blood volume), compromising cardiovascular function, impeding heat dissipation, and causing a steep rise in core temperature.

This will eventually diminish an athlete’s exercise capacity and could lead to heat related illness.

Adequate fluid and electrolyte replacement helps maintain plasma volume so that circulation and sweating are maintained at a good level, meaning your performance doesn’t suffer.


Consuming a strong electrolyte solution in the build-up to a race or training session will boost your salt levels, encouraging 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 which is why planning your hydration strategy is key in this scenario.

Athletes preparing for a hard session or race should take a strong electrolyte drink the night before  to encourage their body to retain fluid, which will boost blood volume.

On the morning of the session or race, 90 minutes before the start, it is recommended that athletes take another bottle of strong electrolyte drink to top-up blood plasma volume.

It is important 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, drinking is unlikely to be necessary. You will lose fluid through sweating but can easily rehydrate to replace any fluid lost and the low level of dehydration you’ll likely suffer will not be enough to impact your performance.

During sessions and events over 90 minutes the need for fluids starts to become apparent for most people and the amount required is largely driven by your sweat rate.

This can vary dramatically from person to person and depend largely on the intensity of the heat you’re exercising in.

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 massive over a period of many hours, personalised sodium supplementation starts to become critical, especially if you’re someone with a high sweat rate or high sweat sodium levels.

A one size fits all approach is tricky, and the best way to make sure you’re drinking the right amount for you, is to create a hydration plan according to your particular needs.

Hydrating after exercise

When your sweat losses have been fairly low (as is the case after many standard training sessions) and when you don’t need to perform again for a while, simply drinking and eating normally is usually enough to replace all 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 in that day, a more proactive approach to rehydration may be needed to help 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 need to drink about 1.5 times more fluid than you have lost, and you need to make sure there’s plenty of sodium either in or with the fluid to account for the salt loss too.

The reason you need to drink so much more than you sweated out is that you inevitably end up peeing some of it out (and perhaps continue sweating after you finish too).

Your drinks need lots of sodium in them to prevent your blood sodium level dropping too low, which would cause your kidneys to significantly ramp up urine production to rebalance your water and sodium levels.

Don’t waste your training

For athletes that put hard work and long hours into training, hydrating appropriately for the conditions helps avoid putting yourself at a disadvantage.

By starting the session properly hydrated, knowing what to drink during exercise and taking care to re-hydrate effectively, you not only reduce unnecessary discomfort, fatigue and muscle weakness, but also allow your body to realise its full potential.

For more advice and information on fuelling and hydration, visit https://www.precisionhydration.com/performance-advice/

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