Electrolyte supplements are not necessary for most leisurely runs in mild temperatures, at sea level, in moderate humidity, and under one hour. If you are running in hot temperatures (or in heavy layers in cold temperatures), you’re running for more than one hour, or you tend to sweat heavily, you may want to use an electrolyte supplement, or at least a beverage with sodium, before and during your run. Running in high levels of humidity or at high altitudes may also necessitate an electrolyte supplement.