The Story Most People Have Heard
Exercise-associated muscle cramp has long been explained as a shortfall of fluid and sodium. It is an intuitive story: you sweat, you lose salt, the muscle seizes. It also matches the experience of athletes who cramp on hot days.
Where the Evidence Gets Complicated
Studies comparing crampers and non-crampers in the same event have not consistently found differences in hydration status or blood sodium. Some athletes cramp while well hydrated. Others lose a great deal of fluid and never cramp at all.
The Neuromuscular Explanation
A second theory holds that cramp comes from muscle fatigue changing the balance between the reflexes that excite a muscle and those that inhibit it. This fits an observation most athletes recognise: cramp tends to arrive late, in the muscles being worked hardest, and often when pace has just lifted.
What This Means in Practice
Neither theory is settled, and they are not mutually exclusive. Sensible training progression, pacing that matches your fitness, and reasonable fluid and sodium intake are all defensible. If cramp is frequent or severe, or happens outside exercise, that is a conversation for a doctor or sports dietitian rather than a change of drink.
Frequently Asked
Does dehydration cause muscle cramp?
It may contribute for some people, but studies comparing athletes who cramp with those who don't have not found a consistent difference in hydration status. It is not the settled explanation it is often presented as.
Will extra salt stop me cramping?
For some athletes it appears to help, but the evidence is mixed and it is not a reliable fix. If you are already taking in sensible amounts of sodium during long efforts, more is unlikely to be the answer.
When should I see someone about cramp?
If cramp is frequent, severe, happens at rest, or comes with other symptoms, see a GP or sports dietitian rather than treating it as a hydration problem.
