When you’re racing for two hours or more you’re right on the threshold at which good hydration practices start to become crucial if you want to perform at your best.

Here's some things to consider when thinking about your marathon hydration strategy...

How to start a marathon hydrated

When people talk about hydration, most of the time it's about what and how much athletes should drink during exercise. These are clearly important questions, but your performance is also massively influenced by how hydrated you are when you start exercising in the first place.

Once you begin sweating you're generally going to be fighting a losing battle against fluid and electrolyte loss, so starting off properly hydrated can be extremely beneficial. When you're properly hydrated you have a larger reservoir of fluid to draw from over time than if you're dehydrated.

Starting well hydrated has other benefits too. Optimal hydration maximises your blood volume and this helps general cardiovascular function and your ability to dissipate the heat produced by your working muscles. This reduces fatigue and enables you to maintain your performance for longer.

Despite the relatively obvious benefits of starting exercise well hydrated, a recent study of over 400 amateur athletes showed that around 31% of them were turning up to training sessions (and, in some cases, competitions) dehydrated!

Here are some tips to help you start well hydrated…

  • DON’T just drink lots of water in the build-up to the race. You can end up diluting your body’s sodium levels before you start, increasing the risk of a potentially race-ruining (and even dangerous) condition called hyponatremia. At best you’ll end up with a lot of fluid sloshing around in your stomach/bladder.
  • Drink a stronger electrolyte drink the night before the race to boost your blood plasma volume. Aim for drinks containing >1,000mg of sodium per litre, like our PH 1500 supplement.
  • Drink another bottle of stronger electrolyte drink about 90 mins before you start to top-up your blood plasma volume. Finish your drink >45 minutes before you set off to give your body time to fully absorb what it needs and remove any excess.
  • Adding additional sodium to your pre-race drinks (and meals) helps you absorb and retain more fluid in your bloodstream. This means you’ll have a bigger reservoir of electrolytes/ fluids to draw upon once the race begins and you start sweating some of it out. Having more blood makes it easier for your cardiovascular system to meet the competing demands of cooling you down and delivering oxygen to your muscles.

Read more about how to start hydrated.

What to drink during a marathon

How much should you drink?

Every athlete is different but, as a rule of thumb, very few runners can comfortably drink much more than 750ml (24oz) per hour - especially when running hard - so unless experience tells you otherwise, it’s unlikely you’ll need to drink more than that, especially if you got to the start line well hydrated.

What should you drink?

Personalising your hydration strategy could really make a tangible difference to your result.

That’s because everyone loses a different amount of sodium in their sweat and, if you don’t get replacing that right, you risk hydration-related issues like cramp, dehydration and hyponatremia.

Maintaining the sodium levels in your blood is crucial to performing at your best when you're working hard. Sodium helps you absorb and retain fluid, which keeps your blood volume up, reducing cardiovascular strain, fatigue and potentially helping you avoid cramping up.

Just drinking water when sweating over long periods dilutes your sodium levels, which can really impact your performance and could lead to hyponatremia, which can have some nasty consequences as highlighted in last year’s London Marathon where one runner ended up in a coma with the condition.

Of course, this is an extreme and rare example but it does highlight how bad things can get if you get your hydration strategy badly wrong.

How much sodium you lose is largely genetically determined and doesn’t change too much due to acclimation, diet etc. So, a ‘one-size-fits-all’ approach to hydration just doesn’t work.

Take the Fuel & Hydration Planner as a starting point for tailoring your hydration plan to your needs:

How to rehydrate properly after a marathon

You should be able to top up on the fluids and electrolytes lost in your sweat through the food and drink you normally eat in the hours after the race.

If you struggle with cramp, or feel particularly dehydrated, some more deliberate fluid intake and sodium supplementation might be helpful. Here’s some advice on how to speed up your recovery by rehydrating more effectively.

We hope you find this useful as you look for your best perform yet! If you have any questions about hydration at all, you can email our Athlete Support Team at hello@pfandh.com.

Enjoy your race!

Further reading