When injury sets in, muscles become stationary. An injured muscle usually experiences little - if any - movement. Fluid (swelling) builds up between the cells and they begin to lose their strength. Excessive fluid buildup known as edema, is detrimental to any healing pricess. Not only does it cause swelling around the injured area, but it also prevents removal of waste products and hinders circulation. Electrotherapy stimulates injured muscles to help speed up the healing process.