A charley horse is nothing more than a muscle spasm that, while quick and harmless, can still be very painful. Muscle spasms commonly occur when your electrolytes are imbalanced, you're dehydrated, or that muscle is overworked. For instance, when muscles suddenly contract, your body's electrolytes can become imbalanced, causing nerves to fire uncontrollably. This is when charley horses happen.
Mix all the ingredients together, and enjoy.