Physical therapists use this treatment modality for a number of reasons. The sound waves produced by the ultrasound machine are transmitted into the area to be treated. They penetrate the muscles to cause deep tissue/muscle warming. This promotes tissue relaxation and therefore is useful in treating muscle tightness and spasms. The warming effect of the sound waves also cause increase circulation to the area that assists in healing. The physical therapist can also adjust the frequency on the machine to use waves that will decrease inflammation.