Isotonic vs electrolyte drinks: which one belongs in your Hyrox kit
Walk into any supplement shop and the hydration shelf looks like one category. Isotonic drinks, electrolyte tabs, hydration powders, all promising the same thing. They do different jobs, and picking the wrong one on race day costs you.
Here's the difference that matters, and how to use each one across a Hyrox block.
What "isotonic" actually means
Isotonic describes how concentrated a drink is. An isotonic drink sits at roughly the same particle concentration as your blood, around 280-330 mOsm/kg. That lets it leave your stomach and get into your bloodstream quickly, which is the whole point during exercise.
Most isotonic sports drinks carry two things: carbohydrate (usually 4-8g per 100ml) and sodium. The carbs give you fuel. The sodium helps you hold on to the fluid and speeds up absorption. The American College of Sports Medicine has recommended this carb-plus-sodium format for endurance fluid replacement for years (ACSM position stand on fluid replacement).
So an isotonic drink is a fuelling drink that also hydrates you. That's the key.
What an electrolyte drink is built for
An electrolyte drink is built to replace what you sweat out: sodium first, then smaller amounts of potassium, magnesium and calcium. Most are low-carb or carb-free.
You lose a lot of sodium when you sweat, and the amount varies hugely between people. Research on sweat sodium puts typical losses between 400 and 1,500mg per litre of sweat, with some athletes well outside that range (sweat electrolyte research on PubMed). In a hot Hyrox venue with an hour of non-stop work, that adds up.
An electrolyte drink sorts the salt side and keeps the sugar low. That's useful when you've already fuelled and just need to stay topped up.
Our own Electrolyte+ sits in this camp. Each stick has 1500mg of electrolytes plus 500mg lion's mane and 500mg maca, and it's built for topping up.
The Hyrox problem: one hour, mixed demands
Hyrox is roughly an hour of running broken up by eight functional stations. You're redlining, then transitioning, then redlining again, which is a long way from a marathoner's steady sipping.
That changes how you hydrate. A stomach full of sugary isotonic drink while you're gasping through burpee broad jumps is a recipe for a stitch. Go in under-salted, especially in a hot hall, and you'll be cramping by the sled.
So the right drink depends on the timing.
Before the race
This is where carbohydrate earns its place. In the two to three hours before you start, an isotonic drink tops up your fluid and your fuel at the same time. Pair it with your pre-race meal and you'll walk to the start line hydrated and stocked. Our pre-race meal timing guide covers the food side.
During the race
Keep it simple. Most athletes finishing in 60-90 minutes need very little fluid mid-race, and heavy drinking between stations does more harm than good. If you drink at all, small sips of an electrolyte or light isotonic drink at the water stations are plenty. Aim to arrive at the start already hydrated so there's nothing to fix on the floor.
After the race
Now you're replacing losses. An electrolyte drink helps you rehydrate properly, because plain water dilutes your blood sodium and a lot of it goes straight through you. Adding sodium to your recovery drink helps you keep what you drink.
How to choose, in one line
If you need fuel, reach for isotonic. If you need salt with little sugar, reach for electrolyte. Most Hyrox athletes want isotonic in the hours before and electrolyte for topping up and recovering.
The mistake is treating them as interchangeable and grabbing whatever's nearest. They solve different problems.
A note on sweat rate
You can guess at this, or you can measure it. Weigh yourself naked before a hard hour-long session and again after, without drinking. Each kilo lost is roughly a litre of sweat. Do it a few times in different conditions and you'll know whether you're a heavy, salty sweater who needs to put sodium first, or someone who barely loses much at all. That one number tells you more than any label.
Consistency matters most here. A hydration plan you actually follow on race morning beats a perfect one you make up at 6am and forget.
FAQ
Can I just drink water for Hyrox? For a single hour-long race, if you arrive well hydrated, water is often fine during. The bigger risk is starting under-hydrated or under-salted, and you fix that before and after the race.
Are isotonic drinks bad because of the sugar? The carbohydrate is the useful part when you need fuel. It only causes trouble when you drink a fuelling drink at a moment you needed a salt drink, or sip sugar all day out of habit.
Do I need potassium and magnesium too? Sodium is the electrolyte you lose in by far the largest amounts, so it does most of the work. Potassium, magnesium and calcium matter too, and sodium comes first.
Start with your sweat rate, then pick the drink that fits the moment.