The word electrolyte is often bandied about by exercise enthusiasts and people who work and play in the heat. Electrolytes are necessary to a range of vital functions in the human body -- like transmitting signals to nerves, contracting muscles and ensuring that water gets to where it needs to be [source: Medical Dictionary]. Potassium is one of the most important electrolytes, but when you sweat, potassium is slowly flushed out of your system. A variety of energy and recovery drinks provide potassium. Bananas are an excellent, natural source of potassium. Grab one before, during or after your day in the heat -- it's also easy to digest.