Developed with an Olympic champion and performance nutritionists
Tom DigbyOlympic Champion 2024 · Co-founderRowed the men’s eight in Paris. Built the formula around what three hours of work actually costs you.
Gareth NicholasPerformance nutritionistSet the sodium, potassium and magnesium doses against real sweat-loss data rather than taste.
Hélène de FrancePerformance nutritionist · Olympic medallistSigned off the formulation for athletes who are subject to testing.
Informed Sport certified✦Batch-tested for banned substances✦Made in Germany✦Zero sugar✦Sixty-day money-back guarantee✦7,000+ athletes✦4.8★ on Trustpilot✦Informed Sport certified✦Batch-tested for banned substances✦Made in Germany✦Zero sugar✦Sixty-day money-back guarantee✦7,000+ athletes✦4.8★ on Trustpilot✦
Reason 01
You went out faster than you trained
This is the most reliable predictor there is, and almost nobody wants to hear it. When researchers followed 210 Ironman triathletes, what predicted cramping wasn’t dehydration and it wasn’t falling sodium. It was going harder than their own normal — and having cramped before.
The mechanism is the same every time. A muscle pushed past what it’s conditioned for fatigues, the nerves controlling it misfire, the relax signal stops arriving, the fibres lock. That’s why cramps arrive late — and why pace, not your bottle, is top of this list.
Run the first third slightly too easy. If you finish strong, you paced it right.
Reason 02
Your training load jumped
The second-biggest lever, and the one most often pulled by accident. A big week after a quiet month, a new hill session, a first long ride of the season — the fibres get asked a question they haven’t rehearsed, and they fatigue earlier than your fitness suggests they should.
This is why cramping clusters in two places: early season, and in the three weeks after someone decides to get serious. Both are load jumps. Neither the cause nor the fix is glamorous, which is presumably why you’ve read ten articles about electrolytes and none about calf raises.
Build gradually, and lift. Strength work raises the fatigue threshold of the exact fibres that lock up.
Reason 03
The effort was longer — or on a surface — you’ve never rehearsed
Duration matters independently of pace. A muscle held in a repeating contraction cycle for three hours behaves differently from the same muscle at ninety minutes, even at identical effort. If your longest run is 25km and you’re racing 42, the last 17 are being run by a system with no reference for what it’s doing.
Surface counts too, and almost nobody plans for it. Train exclusively on treadmill or grass and a road or track race is a shock to a muscle that has never absorbed that much ground force.
If the race is longer or harder underfoot than anything you’ve done, plan for the last quarter to be a different sport.
Intermission
Three to go — and only one of them you can fix this week.
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Reason 04
Heat and fatigue stacked on the same day
Neither is the cause alone. Together they lower the threshold at which everything else goes wrong. A hot race raises sweat rate. A short night raises perceived effort at every pace. A hard week going in means you start already partway to the fatigue that triggers the misfire.
This is why your cramping is inconsistent — why you can race the same distance twice and only lock up once. It isn’t random. It’s a threshold, and the conditions decide how close to it you start.
Taper properly and sleep the week before, not just the night before. Both are anti-cramp equipment.
Reason 05
You went in on an empty tank
Low glycogen means earlier fatigue. Earlier fatigue means earlier misfire. That’s the whole chain, and it’s why fuelling belongs on a cramping list at all.
Carb-load across the 48–72 hours before a long race, and take 60–90g of carbohydrate per hour during it. Most age-group athletes take roughly half that and describe the last hour as the wheels coming off, without connecting it to what they didn’t eat.
We don’t sell carbohydrate. We’re telling you anyway, because an article about cramping that skips fuelling to reach the electrolytes faster is an article selling you something.
Fix your fuelling first. It does more for your last 10km than anything else here.
Reason 06 The one you can fix this week
You replaced what you sweat with something that has none of it in it
Sweat is not water. It carries roughly 600mg of sodium per litre out of you, and a hot long session can cost more than a litre an hour. Sodium is the currency the signal to contract and relax is paid in.
Here’s the part that should change what’s in your bottle. In a 2019 study, athletes who rehydrated with plain water after heavy sweating became measurably more susceptible to cramp, not less. Those given an electrolyte solution became less susceptible. Plain water didn’t just fail to help — it moved the threshold the wrong way.
Under 45 minutes, water is fine. Over 45, you need more than water. It takes ninety seconds and it’s the only item here that doesn’t take a training block.
So, what’s actually in the stick
One stick. Three things your sweat takes out.
Not a multivitamin, not a fuel drink. Three electrolytes at the doses a real sweat rate actually costs you, and nothing else competing for space.
Every dose, on the label
Per drink
Hydrate
Why it’s there
Sodium
593 mg
Replaces what roughly a litre of sweat takes out
Potassium
402 mg
Contributes to normal muscle function
Magnesium
81 mg
Contributes to normal muscle function and to the reduction of tiredness and fatigue
Sugar
0 g
Nothing to spike, nothing to settle
Cost
£0.67
Per drink at the 6-box tier
Informed Sport certified and batch-tested for banned substances. Manufactured in Germany.
Most sports drinks on a supermarket shelf were built for a different job: they’re carbohydrate drinks with a little salt added. Useful for fuelling, close to useless for replacing sweat.
How much sodium per serving?
Under 300mg and it isn’t a sweat-replacement product, whatever the front says.
What’s the sugar-to-electrolyte ratio?
If sugar is the first ingredient, you bought a fuel drink.
Is there potassium and magnesium at all?
Or just sodium and flavouring?
Most fail at least two. That isn’t a scandal — they were built for a different problem. It’s just worth knowing which problem you’re solving.
Kaiju was built by Tom Digby, Olympic Champion 2024, who developed it to solve his own cramping — alongside a scientific committee of performance nutritionists.
The starting point wasn’t a market gap. It was that the drinks available to a full-time athlete were built for either the supermarket or the laboratory, and neither was dosed for what actually leaves your body over three hours of work. Most of what was on the label had been chosen to survive a taste test.
So the brief was narrow and slightly boring: dose it for real sweat loss, take the sugar out, get it certified so people who get tested can use it, and add nothing that’s only there to make the front of the sachet more exciting. That’s the whole product. It isn’t a breakthrough. It’s an honest dose.
Choose your plan
Cover reason 06, every session.
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£22.68 — £7.02 less, 24% off, plus the £9.90 bottle free.
“I was sceptical at first because I usually just drink water on my runs and that’s enough… What I mainly noticed is that I felt less wrung out afterwards.”
— JP
★★★★★
“I loved it during the ride — no fatigue at all on my first 138km. Brilliant, no cramps.”
— Christophe G.
★★★★★
“I didn’t get any cramps, and I had less leg pain after the race.”
— Édouard O.
★★★★★
“The taste is a bit surprising on the first sip, but honestly it’s so pleasant. Above all you don’t get tired of it, unlike other brands that taste chemical or too sweet.”
— Rosa O.
Verified Trustpilot reviews, translated from French.
60Days
Try it for sixty days. On us.
Not “unopened”. Use the box. Run on it. If your long sessions feel the same as they did on water, tell us and we’ll give you your money back — you don’t need to send anything back.
Questions, answered honestly
Six questions.
Will this stop me cramping?
No, and be suspicious of anything that says it will. Cramping has at least six contributing factors and five of them are training factors. This closes one of them — the one you can close this week.
Can I just use salt and water?
Yes. 500ml of water, half a teaspoon of salt, a squeeze of lemon, a pinch of sugar — that’s a functional electrolyte drink for a few cents, and on an easy week it’s genuinely fine. What you lose is precision and repeatability: you can’t taste 600mg, and you can’t reproduce it at kilometre 30 with cold hands. Table salt also gives you sodium and nothing else — no potassium, no magnesium.
What about the cramp that wakes me at night?
Same chain, different moment. A fatigued muscle and a misfiring nerve don’t check the clock. Night cramps cluster after hard training days and after days when sodium went out and didn’t come back — which is why they follow the session rather than accompany it. Get your sodium in during and after training, not at eleven at night with a locked calf.
When will I notice anything?
Most people notice it on the first long session, as an absence — less wrung-out afterwards. If your sessions are under 45 minutes you may notice nothing, and that’s the correct result.
How does it taste?
Light, and less sweet than you’re expecting because there’s no sugar in it. Some people find the first sip surprising. A few find it too much — if you’re one of them, dilute in 750ml instead of 500ml, which several long-time users prefer anyway.
Is it safe if I get drug tested?
Yes. Informed Sport certified and batch-tested for banned substances. That certification is why several of the athletes using it chose it.
Five of these take a training block. One takes ninety seconds.
You now know more about why you cramp than the ad that brought you here promised. Most of it you can’t buy, and we’ve spent 3,000 words saying so.
Train specific · arrive on fresh legs · full carb tank · 60–90g carbs an hour · sodium from the first kilometre, not from the first cramp.
The last of those is the one you can fix this week.
Sixty days on us · Informed Sport certified · cancel anytime
Food supplement. Not a substitute for a varied and balanced diet or a healthy lifestyle. Nutrition claims made per the EU Register of authorised health claims. Individual results vary. If you cramp frequently, severely, or at rest, see a doctor — persistent cramping can have causes unrelated to training or hydration.
