By MNRLS
6 minute read
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Start the race hydrated
What to drink during the marathon
After the finish
The marathon distance is the ultimate test for many runners, and getting your hydration right can often make or break your race day. In this simple, easy-to-follow guide, we break down a few key things to consider before your next race.
Start the race hydrated
When it comes to race-day hydration, most runners focus on how much to drink during the race. While that matters, for most of us, how we hydrate before race day has the biggest impact on performance.
Rather than overloading on fluids at the last minute and feeling bloated, the goal is to arrive at the start line already hydrated. This approach is outlined in this 2007 study on pre-hydration and performance.
The day before the race
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Drink fluids as you normally would throughout the day
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Add electrolytes to your fluids to support hydration
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Include a little extra salt in your meals
A simple check: you should feel normal, not thirsty, not heavy, and not constantly needing the toilet.
Race morning
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On race morning, drink to thirst rather than forcing fluids
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Include electrolytes with your fluids
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Ease off heavy drinking 45 minutes before your start time
What to drink during the marathon
How much fluid should you drink?
A practical starting range for all runners is 400ml-800ml per hour. You should test how much fluid you need during your run in the training leading up to your race.
The easiest way to achieve this on race day is:
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Small sips every 10-15 minutes if you're carrying water or a small drink at most aid stations
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Try and keep it consistent rather than random
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If your stomach feels sloshy then back off for 10 minutes, then restart with smaller sips
If you're having to use the bathroom multiple times mid-race, that is often a sign you are drinking more than you need.
Why electrolytes and sodium matter
For marathon efforts, electrolytes (and sodium in particular), play a huge role in maintaining hydration during the race. As we sweat, we lose both fluid and sodium. Replacing only water doesn’t match those losses and can contribute to issues like cramping, dehydration, and in rare cases, low blood sodium. Matching both fluid and sodium losses during the race helps support performance and reduce that risk.
The amount that we sweat varies from runner to runner, and the amount of sodium lost in that sweat is also highly individual. Although sweat loss is different for everybody, data shows that the average runner loses around 1 litre of sweat per hour, containing just over 800mg of sodium. For most runners, aiming for approximately 800mg of sodium per hour is a safe guide.
If you’ve hydrated well in the days leading up to the race and on race morning, electrolyte intake during the race becomes less important than it is for someone starting under-hydrated. Though it can still provide support, especially over longer or faster efforts.
A simple sodium target
Start here, then adjust based on your own long runs:
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Aim for 500–800mg of sodium per hour alongside your water
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In warmer conditions, increase this to 600–1000mg of sodium per hour
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Consider a sweat test if you’d like to tailor electrolyte intake to your individual needs
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If you’re unable to take electrolytes during the race, don’t panic, just focus on hydrating well with electrolytes in the days and morning before, then drink water at each aid station during the race
What happens if you only drink water?
If you are drinking large volumes of plain water, you can dilute blood sodium. That is the key risk highlighted in the 2015 consensus statement. Electrolytes do not make you invincible, but they make your hydration strategy more aligned with what you are actually losing.
If you want an easy way to build this in without overthinking labels, you can use an electrolyte drink as your base and top up with water as needed. If you want to try our approach, here is our electrolyte blend: MNRLS Electrolytes.
After the finish
After the marathon is finished, don't over complicate rehydration and recovery.
If you've hydrated with electrolytes pre-race and during, then:
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simply grab a drink at the race line
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eat a proper meal that includes salt
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keep sipping fluids steadily over the next few hours.
Electrolytes post-race will support recovery, so if you do feel particularly dehydrated then consuming an electrolyte supplement can help.
Sodium helps because it affects how much of what you drink your body actually keeps. It’s not just about how much you drink, but how much of it stays with you. Research from controlled rehydration studies shows that drinks containing sodium improve fluid retention and reduce urine output compared to plain water.
We hope you find this useful as you look to take on the marathon. If you’re looking for clean, great-tasting electrolytes to support training and race day, head over to our shop at mnrls.co.uk.
If you have any questions at all, drop us a message via Instagram at @mnrlsuk.