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It seems like a reasonably straightforward thing, but when you’re running ultramarathons, what you drink can be the difference between success and failure.

During a long race it’s important to ensure you’re replacing what you lose through sweat to ensure your body has all the resources it needs to keep you going right to the finish line.

We all sweat, but no two people sweat in quite the same way. Sweat rate - that is the amount of fluid you lose per hour - varies. And so does the concentration of electrolytes each individual loses in that sweat.

Being intentional about hydration is particularly important for heavy sweaters and for salty sweaters (those who lose a lot of electrolytes when they sweat). And it’s absolutely vital for people like me who tick both those boxes.

Although sweat contains a number of electrolytes, we are going to focus on the two that have the greatest impact on runners - sodium and chloride which go together to form salt.

Sodium chloride is important for runners because when we don’t have enough in our systems it can lead to muscle cramps, a loss of cognitive function and a reduction in blood volume.

This “thickening” of the blood is a shocker for runners because it means the heart has to work harder to pump blood around the body, the end result being a pretty dramatic fall in running efficiency. In other words, you’re having to work harder to run at a consistent pace as the sodium levels in your body fall.

Your body can’t manufacture sodium which means as sweat takes it out of your system, you need to replace it.

That means, for runs that last more than about 90 minutes, it’s not enough to just drink water. Only drinking when you are thirsty is no good - that just means you’re playing catch-up because you’re already dehydrated.

Mimicking someone else’s plan won’t work because we all sweat in our own unique ways. And just guessing how much electrolytes you need to take on isn’t a reliable hydration strategy either.

If all this seems a bit hopeless, don’t lose heart … there is a methodical way to approach hydration, and it’s a game-changer for long runs. To give yourself the best shot at success, you can use personalised data to create a race-specific hydration plan.

To build this you first need the data and that’s a two-step process. You need to calculate what volume of sweat you lose per hour when you run, and you need to take a sweat test to work out how salty that sweat is.

I wrote about both in more depth last week, but essentially you can do the first yourself but you’ll need to see the professionals for the sweat test. While there is an outlay for this, in my view it’s well and truly worth it.

Having done both, I know I lose 2.4 litres of sweat per hour, which is on the high side, and that sweat contains almost 1,200 milligrams of sodium per litre, which is also high. So now I have the data, what do I do with it?

The easiest step from here is to use a calculator and one of the best around is on the Precision Fuel & Hydration website. This calculator asks a number of questions and uses the information to produce a race-day plan.

Along with your sweat rate and sodium data, you can input the specific race you’re entering, the distance, the intensity you want to race at, your estimated finish time, your propensity for cramping, how hot you expect it to be on race day and basic data like age, weight and gender.

It uses this info to spit you out a race day plan that sets out how much sodium and fluid you’ll need to take on board each hour.

In the interests of research, I put this to the test using the Blackall 100, a notoriously hot race, as the example. (Please note, although it’s in my thoughts this is not me committing to this race … at least not yet!)

The sharp-eyed among you will note this plan suggests I drink between 450 millilitres and 750 millilitres of fluid per hour, when my sweat test showed I lose a lot more than that. The reality is you don’t need to replace all the fluid you sweat.

As long as you start the race well hydrated, your body will cope with becoming a little dehydrated over the journey. Plus, it’s hard to imagine actually stomaching 2.4 litres every hour. That amount of liquid sloshing around your stomach while running would be extremly uncomfortable.

It’s more important to ensure your sodium intake is adequate, because that’s the key ingredient to prevent your performance from dropping off later in the race. There are a variety of ways of ingesting sodium.

Using soluble tablets in your drink bottles is one of the easiest ways, but you can also take sodium capsules, salt chews or good, old-fashioned salt tablets. I’ve downed sachets of table salt during races in the past and you can also increase your sodium by eating real foods - like a handful of salted potato chips.

Of course, now you know what you need to take on board during the race, you need to figure out how you’re going to carry it all. For an ultra, I definitely need to wear a running vest with a decent-sized hydration bladder - 1.5 litres or even 2 litres.

But belts and even hand-held bottles may suffice for others. It’s also worth factoring aid stations into your planning because that’s where you’ll be able to top up with water. Many races will have an electrolyte drink on offer at aid stations, but given they’re mixed by volunteers the concentration ranges from barely a hint of added electrolyte to strong enough to leave you gagging.

So if you’ve gone to the trouble of working out what you need, you’re better off carrying the electrolyte with you in the form of powder, tablets, capsules or chews, and just grabbing water at the aid stations.

Finally, don’t leave all this until race day. Like everything else in running, and in life, you’ll get better with practice. So use the long runs in your training block to start experimenting with your race-day plan.

With a little science, a little effort and a little planning, you can take the guesswork out of one of the most important ingredients in a successful race day.

Upcoming Events

There are way too many events for me to list everything that’s happening around the country, but here is a selection of upcoming races (with a bias towards South East Queensland).

The Running Calendar website is a great source if you want a comprehensive understanding of what’s available around