Muscle cells reach their action potential and contract when sodium and potassium ions cross the cell membrane in sufficient quantities to cause a depolarization which leads to a contraction. Hyperkalemia increases the potassium level in the extracellular fluid which decreases the concentration gradient and slows the movement of potassium out of the cell which decreases the cell’s ability to reach the threshold potential. Hypernatremia increases the concentration gradient which speeds the movement of sodium across the membrane and the cell reaches the threshold more quickly. Calcium is needed to activate a muscle contraction, and hypercalcemia makes more calcium available. Hyperphosphatemia increases the phosphate available to be utilized as adenosine triphosphate, which is required for muscle contraction.