Category: Heat & Race Execution

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.

1. Slow to a walk or stop.
2. Stretch the muscle gently and hold. For a calf, straighten the knee and pull your toes towards your shin.
3. Walk until the tightness eases, then restart below your earlier pace.
4. 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.

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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

Last updated: 21 September 2026

Drink to thirst on short runs and check your own numbers on long ones. Athletes sweat anywhere from 0.5 to 2 litres an hour, so no single target fits everyone. In heat, sodium matters once a session passes an hour, and overdrinking plain water carries its own risk.

How much do you actually sweat when you run in Malaysia?

More than most people guess, and the gap between runners is huge. Athletes in general sweat between about 0.5 and 2 litres an hour, and a few pass 3 litres (Baker, 2017). The KL Marathon’s own weather page puts Kuala Lumpur at 29 to 35°C in the day with humidity around 80%. In air that wet, sweat evaporates badly, so a lot of it drips off without cooling you. You lose the water and get less of the benefit.

The arithmetic gets uncomfortable fast. A 70 kg runner sweating 1.5 litres an hour loses 3 litres in two hours. That is 4.3% of body mass if none of it is replaced. The ACSM’s 2007 position stand sets the line at about 2%, which is 1.4 kg for the same runner.

Should you drink to thirst or follow a plan?

For most recreational runners, drink to thirst first, then check yourself with a weigh-in. Expert guidance splits on this. The ACSM’s 2007 position stand says the aim is to keep weight loss under 2% and to tailor the plan to the person. The 2015 international consensus on exercise-associated hyponatraemia goes further and says to use thirst as your guide, because drinking beyond thirst has been linked to deaths in athletes, marathon runners among them.

Our view: on easy and moderate runs, thirst is good enough. A plan starts to earn its place on long, hot, hard efforts, and only after you’ve measured your own sweat.

How do you measure your own sweat rate?

Weigh yourself before and after a one-hour run, and count everything you drink. The ACSM lists this as the way to estimate individual sweat rates.

1. Weigh yourself in minimal dry clothing before the run, after using the toilet.
2. Run 60 minutes at the effort you’d race at. Note how much you drink.
3. Towel off and weigh again in the same clothing.
4. Sweat loss in litres = kilograms lost + litres drunk (1 kg is about 1 litre).

Example, for illustration only: 70.0 kg before, 68.9 kg after, 0.5 litres drunk. That is 1.1 + 0.5 = 1.6 litres an hour.

If you lose more than about 2% of your starting weight, you drank too little for that run. If your weight goes up, you drank more than you sweated, and that is the direction to worry about.

One test is one snapshot. Sweat rate moves with pace, humidity and heat acclimatisation (Baker, 2017), so a test in an air-conditioned gym tells you little about race morning. Repeat it in the conditions you’ll race in.

Is plain water enough in the heat?

For runs under an hour, yes. Past an hour you are also losing sodium, and how much varies enormously. Baker’s review puts sweat sodium at roughly 10 to 90 mmol per litre. One mmol of sodium is 23 mg, so that works out to about 230 to 2,070 mg in every litre of sweat. A runner losing 1 litre an hour at a middling 40 mmol/L gives up about 920 mg an hour.

The ACSM’s 1996 position stand suggests 0.5 to 0.7 g of sodium per litre of fluid for exercise longer than an hour. Drink 500 ml an hour at that strength and you take in 250 to 350 mg. Against a 920 mg loss, that leaves a wide gap on a long, hot run.

This is where a sodium tablet earns a place. Elec Stamina is a swallow tablet made in China. Each tablet has 220 mg of sodium, and the label suggests 1 to 2 tablets every 10 km, up to 10 a day. At a 6 min/km pace that is 220 to 440 mg an hour, so it covers part of the 920 mg example above, not all of it. It has no immediate effect, so treat it as a schedule item: take it with water at set points in a long session, not as a rescue when you feel bad. It doesn’t replace drinking, and it isn’t a licence to drink more.

For a 45-minute easy run you don’t need it. Water and a normal meal are fine.

What should you drink before a hot run?

About 500 ml roughly two hours before, then let thirst take over. That figure is from the ACSM’s 1996 stand, which also says cool fluid (15 to 22°C) gets drunk more readily. In Malaysia a bottle in your bag won’t stay cool for long. Freeze half of it overnight and top up with water in the morning.

How do you know you’re getting it wrong?

Too little shows up as a weigh-in loss of more than 2%. Too much shows up as weight gain during a long run, puffy fingers, nausea and light-headedness, which are the mild symptoms listed in the 2015 hyponatraemia consensus. These overlap with heat illness. If someone is confused, vomiting or has a bad headache, stop and get medical help.

FAQ

How much water should I drink when running in hot weather?

Drink to thirst on short runs. On long ones, measure your sweat rate and aim to finish within about 2% of your starting weight.

Do I need electrolytes for a 10K?

Usually not. Most recreational 10Ks last under an hour, and the guidance on sodium in fluids starts at exercise longer than an hour.

Can I just drink plain water on a long run?

You can, but it leaves the sodium gap open. Drinking more than thirst asks for is the bigger risk.

Will drinking more stop cramps?

Probably not. The best evidence links cramps to fatigue and pace. See Why Runners Cramp in Malaysian Heat.

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Related: Why Runners Cramp in Malaysian Heat · Elec Stamina

Written by Stamina Sports Malaysia, distributor of Katsuo Stamina in Malaysia since 2015.

Sources

• Baker LB. Sweat Testing Methodology in the Field: Challenges and Best Practices. Sports Science Exchange 161, 2017. Link
• ACSM Position Stand, Exercise and Fluid Replacement. Med Sci Sports Exerc 2007;39(2):377-90. Link
• ACSM Position Stand, Exercise and Fluid Replacement. Med Sci Sports Exerc 1996;28(1):i-vii. Link
• Hew-Butler T et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference. Clin J Sport Med 2015;25(4):303-20. Link
• KL Marathon, Weather. Link