Potassium (K+) is a positive ion which is essential to the depolarization of cells. Depolarization occurs when the threshold energy level is met, there is an electrical pulse will then travel down the length of a nerve cell resulting in a muscle contraction. When the cell is depolarized, sodium and potassium which are positively charged ions move into the cell and negatively charged ions such as chloride move to the outside. This sends a signal down the entire length of a bundle of fibers, spreading a signal for contraction. Healthy pools of electrolytes, which are charged ions, are necessary for the contraction of muscle fibers.
Potassium is one of the most important electrolytes and aids in the prevention of muscle cramping by helping with the re-establishment of polarization following a muscle contraction. This is the reason bananas are often recommended before any extensive physical activity or athletic events take place, they have a high concentration of potassium. That being said, eating an absurd amount of fruit to get high potassium levels is not always ideal, as the sugar in fruit, which is fructose, can lead to intestinal distress and is poorly utilized as energy.
Potassium can also be obtained through certain pre-workout supplements, like Anavite, which offer a large dose of potassium to aid in muscle contraction while avoiding the negative effects substances such as fructose may have on energy production.