Electrolytes are minerals like sodium, potassium, and magnesium that your body loses through sweat and that help regulate fluid balance, muscle function, and nerve signals. Runners often replace them with sports drinks, gels, or salt tablets during long or hot races to help avoid cramping and dangerously low sodium levels.
Sweat carries away sodium and other minerals along with water, and losing too much can affect muscle function and fluid balance. Replacing them during long efforts helps maintain performance and reduce cramping risk.
You may notice cramping, fatigue, or a general performance drop over a long, hot race. In more serious cases, drinking large amounts of plain water without replacing sodium can contribute to hyponatremia, a dangerous drop in blood sodium.
As a general guide, runs under an hour in mild conditions rarely need them, while anything longer, hotter, or heavier on sweat usually benefits from some replacement. Heavy salty sweaters often notice visible salt residue on their skin or clothing.
Plain water rehydrates but replaces none of the minerals lost in sweat. Electrolyte drinks add sodium and other minerals, and often some carbohydrate, which is useful on longer runs but not necessary for a short easy jog.