Electrolyte

Potassium

Sodium and potassium work as a pair — sodium mostly outside your cells, potassium mostly inside. Every muscle contraction depends on these two trading places across the cell wall, thousands of times a second. When potassium drops, that exchange gets sloppy: muscles cramp, fatigue sets in earlier, and recovery slows. Most athletes get less potassium than they need from food alone, so replacing it alongside sodium keeps the pair balanced instead of fixing one side of the equation.