The leading ideas about the cause of cramps revolve around dehydration, electrolytes, and nerves.
The Dehydration Proposal
You just need more fluids, but studies have shown that athletes who cramped or did not, had zero differences in hydration. More importantly, dehydration can cause gastrointestinal distress, indirectly leading to muscle cramps. No matter what any study says, our performance suffers from dehydration. Our bodies are about 60 – 70% water and maintaining a balance is important. Just ask someone who has run out of fluids during the Dirty Kanza (200 mile gravel race).
The Electrolyte Proposal
It’s all about sodium, potassium and other minerals. The connections between the muscle and nerves become stressed. Depleted electrolytes via excessive sweating and fluid shifts cause the nerves to fire when they shouldn’t as well as not sending appropriate signals to the brain when they should. But studies of Ironman athletes showed little or no difference in electrolytes compared to those who had cramps and those who did not. Sodium loss during exercise varies significantly from person to person. During exercise, some athletes lose at little as a half a gram of salt per hour and others may lose 3 grams. These larger losses of sodium have been linked to muscle cramping and reduced cognitive function.
The Nerve Proposal
Cramping results from a decrease in the coordination between the nerves and muscles; miscommunication between signals that tell a muscle to fire and those that tell it to relax. Think of an electric circuit moving from the spinal cord to the nerves and to the muscles, without telling the brain. Realize that the nerve proposal has not been proven in rigorous studies. One thing the nerve proposal studies confirm is that prolonged exercise at a pace faster than usual training levels have a higher chance of developing and cramps.