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Staying Hydrated During An Ironman

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hydrating fuelling nutrition Ironman triathlon racing

Our friends from Precision Hydration, who help elite triathletes such as Sarah Crowley, Emma Pallant, Sarah Lewis, and Michelle Dillon, have put together this advice on staying hydrated during an Ironman so that you can race and finish strong and healthy. 

Starting well 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. Drinking a strong electrolyte drink to optimise your hydration status before an IRONMAN event can significantly improve your performance.

This is known as "pre-loading" and the practice has been widely studied in the last 20 years or so, both with astronauts and athletes. There's strong evidence that taking in additional sodium with fluids before you start sweating is effective in promoting increased acute fluid retention and in improving endurance performance, especially in the heat. 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.

But typical sports drinks – which generally contain 200 to 500mg of sodium per litre – simply don’t cut it when it comes to pre-loading as they're just way too dilute to make a meaningful difference to blood volume. The reality is it’s not vastly different from drinking water. Instead, look for supplements containing more than 1,000mg of sodium per litre, like PH 1500.

Aim to drink a 500ml bottle of strong electrolyte drink the evening before the race and another around 90 minutes before the swim start. Finish the latter around 45 minutes before you start to allow time to absorb. Be sure to drink the electrolytes in water you’d have drunk anyway so you don’t overdo it. Whatever you do, DON’T just drink lots of plain water before a race! You can end up diluting your blood sodium levels, increasing the risk of a race-ruining condition called hyponatremia.

swimming training hydration triathlon

Staying hydrated during the race

A full distance triathlon race is clearly too long to go without drinking, so you’re going to need to be knocking back a reasonable amount of fluids during the ride/run. The aim is to try to avoid under-drinking to the point that dehydration hampers your performance, whilst avoiding over-drinking, which can lead to hyponatremia.

But it’s not just about getting any old fluids in. Maintaining your blood sodium levels during a race is crucial to performing at your best, especially in the heat. As well as maintaining fluid balance, sodium plays an important role in the absorption of nutrients in the gut, maintaining cognitive function, nerve impulse transmission and muscle contraction.

A 2015 study found that athletes who adequately replaced the sodium lost in their sweat finished a 70.3 triathlon an average of 26 minutes faster than those who didn’t. Sodium depletion is also one cause of cramp and avoiding it could help you have a cramp-free race.

Top Tip: Have a bottle of water by your bike so you can rinse your mouth out before jumping onto the saddle.

cycling Ironman triathlon training racing

During a full distance race, you need to make a conscious effort to stay on top of your fluid and electrolyte replacement throughout the bike leg to avoid dehydration derailing your race later on. This is the best time to get fluids on board because you can carry/drink more easily than when running. Carry an electrolyte drink in your bike bottle(s) during the ride and/or carry some salt capsules for when your pre-mixed drinks run out.

Few people can process more than about 1 litre per hour on the bike, so that’s probably the upper limit of how much you’d need to carry. This is especially important to remember in a long distance race because the risk of hyponatremia from drinking too much is greater than in shorter events.

Most athletes will need to take in between 600ml and 1 litre per hour during a full distance ride. The exact amount depends on the conditions, your own sweat rate, and past experiences, so treat these numbers as a guide only.

Most athletes find they can take in less fluid per hour on the run than they can on the bike, which should give you an idea of the kind of volumes you might be able to tolerate. Experimenting within these guidelines, whilst learning to listen to your body, is the best way to work out how much you need to drink during a race.

Thirsty? Dry mouth? Don’t need to pee once during the last third of the bike ride? You may not be drinking enough. Try to respond to the early signs of thirst and not leave it too late. Bloated? Fluid sloshing around in your stomach? Need to pee more than 3 times? You might be drinking too much. Don't force fluids down if you don’t feel you need them.

Really thirsty? Walk through some aid stations to ensure you get enough fluid on board. A few seconds lost doing this is better than getting very dehydrated later on and risking a DNF! Dumping water or ice over your head at aid stations can also help when it’s very hot! The cooling sensation this triggers means your body has to sweat less to keep itself from boiling over.

water bottle sports supplement hydration triathlon

After the race

Most athletes will finish a long course triathlon dehydrated to some extent and you’ll need to replenish your losses before you’re ready to go again. Most of the time, just drinking water and eating as normal after the race is enough, but if you’re suffering with cramp, feel especially fatigued or you plan to train/race the next day, then a more proactive approach to hydration would be advisable.

In those cases, sip on a 500ml bottle of strong electrolyte drink in the hours after you finish. Research shows that drinks containing sodium enable better re-hydration as it allows your body to hold onto more fluid.

hydration electrolyte supplement

If you want to pick up some electrolytes that match how you sweat, just use the code SUNDRIED15 at to get 15% off your first order.

About the author: Andy Blow founded Precision Hydration to help athletes solve their hydration issues. He has a few top 10 Ironman/70.3 finishes and an Xterra World Age Group title to his name. He has a degree in Sport and Exercise Science and was once the Team Sports Scientist for Benetton and Renault F1 teams.

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