Last updated: 21 September 2026
The best-supported explanation for running cramps is muscle fatigue, not a simple lack of salt. In a study of 210 Ironman triathletes, running faster than usual and having cramped before predicted cramping. Dehydration and blood sodium did not. Once a cramp starts, the usual first move is to slow down and stretch the muscle.
What causes cramps when you run?
Nobody has settled it, but the fatigue explanation has the stronger evidence. There are two main ideas.
The older one says you cramp because sweat has drained your fluid and salt. It’s the idea most of us grew up with. A narrative review of exercise-associated muscle cramps describes it as resting on case series and anecdotal observation, and notes that athletes have cramped while fully hydrated and taking in enough electrolytes.
The newer idea comes mainly from Martin Schwellnus and colleagues in Cape Town. A fatigued muscle loses the normal balance between the signals that tell it to contract and the signals that tell it to relax, and the working muscle locks up. It fits what runners report: cramps hit the muscles doing the most work, late in a hard effort, and runners who cramp almost always feel that muscle tire first. Schwellnus’s 2009 review says the salt and dehydration ideas lack a convincing mechanism and that data are accumulating for the fatigue explanation. He also says more evidence is needed.
What did the Ironman study actually find?
Pace and cramp history predicted cramping better than hydration or blood sodium did. In 2011 Schwellnus, Drew and Collins followed 210 Ironman triathletes and tracked who cramped. Running faster than usual and having cramped before were the predictors. Dehydration and changes in serum sodium were not.
Read plainly, that says a late-race cramp is a pacing problem before it’s a salt problem. If you started faster than you trained for, your muscles were always going to be tired early.
So does sodium matter at all?
Yes, just not as a cure for cramps. Sweat sodium runs from roughly 10 to 90 mmol per litre (Baker, 2017), which is about 230 to 2,070 mg in a litre. A heavy sweater on a long, hot run loses a lot. The ACSM says sodium in drinks helps palatability and fluid retention and may help people who drink large volumes. Those are good reasons to care about sodium in long sessions. They aren’t evidence that sodium stops cramps.
That’s how we see Elec Stamina. It’s a swallow tablet with no immediate effect. It can’t stop a cramp that has already started, and we don’t claim it prevents them. Its job is putting sodium into a long session on a schedule. Each tablet has 220 mg of sodium, and the label suggests 1 to 2 tablets every 10 km. If you cramp in the last hour of a long race, look at pace and training load before you look at salt.
What should you do when a cramp hits?
Slow down and stretch the cramping muscle. Reviews describe stretching as the most effective remedy for an acute cramp.
- Slow to a walk or stop.
- Stretch the muscle gently and hold. For a calf, straighten the knee and pull your toes towards your shin.
- Walk until the tightness eases, then restart below your earlier pace.
- Sip if you’re thirsty. Don’t gulp.
If the same muscle keeps cramping, ease off for the rest of the race. Finishing slower beats not finishing.
How do you make late-race cramps less likely?
Start at or below the pace you’ve trained. The Ironman study points at speed above your usual, so the cheapest fix is a slower first half.
- If you’ve cramped before, run the first half more conservatively. Previous cramps predicted the next one.
- Do long runs at the time of day and in the heat you’ll race in. Malaysia’s big road marathons start very early. The Malaysia Marathon flagged off its full distance at 12.30 am on 30 August 2026, and the KL Standard Chartered Marathon starts at 3.30 am on 4 October. Practise running long in the dark and into the morning heat.
- Follow a drinking and sodium plan for the other reasons above. See Running in Malaysian Heat.
The Ironman study was observational and done in triathletes. It shows what went with cramping, not what caused it, and it may not carry over to a weekend runner doing a 10K.
FAQ
Do electrolyte tablets stop cramps?
There’s no good evidence they do. The stronger studies link cramps to fatigue and pace. Electrolytes still have a job in long, hot sessions, and that job is fluid and sodium balance.
Why do I cramp in races but not in training?
Race effort is usually higher than training effort. In the Ironman study, running faster than usual predicted cramping.
Can you cramp if you’re well hydrated?
Yes. Reviews describe athletes cramping while fully hydrated and supplemented.
When should I see a doctor about cramps?
Cramps that keep happening outside hard exercise, or that come with other symptoms, are worth checking with a doctor.
Related: Running in Malaysian Heat · Elec Stamina
Written by Stamina Sports Malaysia, distributor of Katsuo Stamina in Malaysia since 2015.
Sources
- Schwellnus MP. Cause of Exercise Associated Muscle Cramps (EAMC): altered neuromuscular control, dehydration or electrolyte depletion? Br J Sports Med 2009;43(6):401-408. Link
- Schwellnus MP, Drew N, Collins M. Increased running speed and previous cramps rather than dehydration or serum sodium changes predict exercise-associated muscle cramping: a prospective cohort study in 210 Ironman triathletes. Br J Sports Med 2011;45(8):650-656. Link
- Nelson NL, Churilla JR. A Narrative Review of Exercise-Associated Muscle Cramps: Factors that Contribute to Neuromuscular Fatigue and Management Implications. Muscle Nerve 2016;54(2):177-185. Link
- Baker LB. Sweat Testing Methodology in the Field. Sports Science Exchange 161, 2017. Link
- ACSM Position Stand, Exercise and Fluid Replacement, 1996. Link
- paultan.org, Malaysia Marathon 2026 flag-off times. Link
- KL Marathon, Race Weekend Schedule. Link