6. Muscle cramps are caused by dehydration.
The idea that exercise-related muscle cramps are caused by dehydration and/or electrolyte depletion originated from a single flawed study conducted almost a century ago. More recent science has clearly shown that there is no correlation between dehydration levels and risk of cramping.
Instead, muscle cramping appears to be a symptom of a type of neuromuscular fatigue that is caused by unaccustomed exertion (this is why muscle cramping occurs almost exclusively in races) and occurs in athletes who have some sort of innate susceptibility to cramping. Drinking more fluid and consuming more electrolytes have not been shown to reduce cramping risk in susceptible athletes in races, with the exception of one study showing that sodium-loading before prolonged exercise delayed the onset of cramping.