Cramp, and why the salt tablets did not work

Cramp is the running problem with the largest gap between how confident the advice sounds and how much evidence sits behind it. Almost everyone will tell you it is salt or water. Someone went and checked.

What the evidence actually shows

Eighteen cases and a study of ten people, against four prospective cohorts that went looking and did not find it. That is the evidence base for the thing on the side of the electrolyte sachet.

What the better explanation says

Muscles have protective reflexes. One increases muscle activity, one inhibits it, and normally they balance. Under fatigue, particularly when the muscle is working in a shortened position, that balance shifts: the excitatory side increases and the inhibitory side decreases, and the muscle locks into sustained involuntary contraction¹.

That explains things the chemical version cannot. Why cramp is local rather than general. Why it hits the calf when you push off from the toes, or the hamstring in a sprint finish. Why it strikes late in a race rather than early. And why stretching the muscle stops it within seconds, which no chemical deficiency would do.

What predicts it

The pattern that emerges from studies of cramping athletes is about effort rather than intake.

Running faster than you have trained to run is the recurring feature. So is racing a distance you have not prepared for. So is a history of cramping in previous races, which is the single best predictor anyone has found. Most people cramp in the last third of an event, at the point where fatigue is highest and the muscle is least able to keep its reflexes balanced.

What to do in the moment

Stop and stretch the cramping muscle, gently and sustained, until it releases. For the calf, that is pulling the toes up towards you or leaning into a wall. For the hamstring, straightening the knee. For the foot, pulling the toes back.

Then ease back into movement rather than resuming at the same pace, because a muscle that has just cramped will cramp again if you ask it for the same thing immediately. Most people can keep going at a slightly reduced effort.

What to do beforehand

Train at the intensity you intend to race at, so the muscle has met that demand before. Build the distance properly, so the last third of the race is not the furthest you have been in months. Pace the race conservatively in the first half, which is the single change most likely to help.

Strength work for the muscles that cramp most, usually the calf and the hamstrings, raises the point at which fatigue becomes a problem.

None of that is exciting, and all of it is more likely to work than a drink.

The honest caveats

Two things to be fair about.

Absence of evidence for the electrolyte hypothesis is not the same as proof it plays no role in anyone. Some individuals with very high sweat rates and very salty sweat may be a different case, and that is a reason for an individual assessment rather than a general rule.

And the altered neuromuscular control model, while better supported, is still a model. The review that argues for it says explicitly that further evidence is required¹.

There is also a fluid consideration that runs the other way. In the heat, the instinct to drink more to prevent cramp can push people towards drinking too much, which carries its own risk². Our article on heat and fluid covers that.

When to get it looked at

Dark urine with severe muscle pain after hard exercise is the one to act on quickly rather than wait on.