Cramp is a nerve problem wearing a hydration costume

Evidence points to fatigued neural control of the muscle rather than salt and water, which is why drinking more rarely stops it.

Ninety minutes in, a hamstring locks solid, and somebody runs on with an electrolyte sachet. It usually works, or seems to, and I would gently suggest that what fixed it was the two minutes of lying still and the stretch, not the sachet.

The dehydration story has an obvious appeal and some awkward problems. Cramping athletes do not reliably show worse hydration or lower blood sodium than non-cramping athletes in the same event. Cramp appears in cool conditions and in swimmers. It strikes one muscle group while every other muscle in the body, exposed to identical blood chemistry, behaves normally. A whole-body deficiency that expresses itself in a single calf is a strange kind of deficiency.

The alternative account is local and neural. Sustained work fatigues the muscle, and fatigue alters the balance between two reflex inputs. Muscle spindle activity, which excites the motor neuron, increases. Golgi tendon organ activity, which inhibits it, decreases, especially when the muscle is contracting in a shortened position. The motor neuron pool becomes hyperexcitable and starts firing without being asked. That produces exactly what is observed, which is a sustained involuntary contraction in the specific muscle that was working, appearing at the specific moment of greatest fatigue, most often when the muscle is already short.

The predictors line up with that. Cramp correlates with going faster than usual relative to your training, with racing rather than training, with previous cramping history, and with the late stages of an event. All fatigue variables.

It also explains why stretching relieves it. Lengthening the muscle reloads the tendon organs, restores the inhibitory signal, and the contraction switches off. That is a mechanical fix to a neural problem, applied in about ten seconds.

The pickle juice observation fits the same frame, since a strong taste in the mouth appears to interrupt the reflex through the nervous system far faster than anything swallowed could reach a muscle.

None of this means fluid and sodium are unimportant for performance. They are. They are simply the wrong lever for this particular symptom.

Train for the intensity you intend to race at and you will cramp less. Drink more and you will mostly just need the toilet.