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 don't do the same job, and picking the wrong one on race day costs you.
Here's the difference that actually matters, and how to use each one across a Hyrox block.
What "isotonic" actually means
Isotonic describes the concentration of a fluid, not what's in it. An isotonic drink sits at roughly the same particle concentration as your blood, around 280 to 330 mOsm/kg. That balance lets it empty from your stomach and cross into your bloodstream quickly, which is the whole point during exercise.
Most isotonic sports drinks carry two things: carbohydrate (usually 4 to 8 grams per 100ml) and sodium. The carbs give you fuel. The sodium helps you hold onto the fluid and drives 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 happens to hydrate. That's the key.
What an electrolyte drink is built for
An electrolyte drink is built to replace what you lose in sweat: sodium first, then smaller amounts of potassium, magnesium, and calcium. Most are low in carbohydrate or carb-free.
You lose a lot of sodium when you sweat, and the rate varies hugely between people. Research on sweat sodium puts typical losses somewhere between 400 and 1,500mg of sodium 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 continuous work, that adds up.
An electrolyte drink solves the salt problem without loading you with sugar. That's useful when you've already fuelled and you just need to stay topped up.
Our own Electrolyte+ sits in this camp. It leans on a calcium-heavy formula and includes Lion's Mane and Maca, and it's built for topping up rather than fuelling.
The Hyrox problem: one hour, mixed demands
Hyrox is roughly an hour of running broken up by eight functional stations. You're not sipping steadily like a marathoner. You're redlining, then transitioning, then redlining again.
That changes how you hydrate. A stomach full of sugary isotonic fluid while you're gasping through burpee broad jumps is a recipe for a stitch. But going in under-salted, especially in a hot hall, leaves you cramping by the sled.
So the answer depends on timing, not on which drink is "better."
Before the race
This is where carbohydrate earns its place. In the two to three hours before you start, an isotonic drink tops up fluid and tops off your fuel at the same time. Pair it with your pre-race meal and you 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 to 90 minutes don't need much 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 fluid at the water stations is plenty. The goal is to arrive at the start already hydrated, not to fix it 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 just makes you pee it back out. Adding sodium to your recovery fluid helps you actually retain what you drink.
How to choose, in one line
If you need fuel, reach for isotonic. If you need salt and not 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're solving 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 kilogram lost is roughly a litre of sweat. Do that a few times across different conditions and you'll know whether you're a heavy, salty sweater who needs to prioritise sodium, or someone who barely loses much at all. That one number tells you more than any label.
Consistency beats optimisation here. A hydration plan you actually follow on race morning beats a perfect one you improvise 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 going in under-hydrated or under-salted, which is a before-and-after problem, not a during-the-race one.
Are isotonic drinks bad because of the sugar? No. The carbohydrate is the useful part when you need fuel. It's only a problem when you drink a fuelling drink at a moment you needed a salt drink, or when you sip sugar all day out of habit.
Do I need potassium and magnesium too? Sodium is the electrolyte you lose in the largest amounts by far, so it does most of the work. Potassium, magnesium, and calcium matter, but chasing them at the expense of sodium is the wrong order of priorities.
Build for athletes who train with intent. Start with your sweat rate, then pick the drink that fits the moment.