Ultrasound therapy is used for therapeutic effects. Ultrasound uses acoustic energy at a high frequency. A continuous wave produces thermal effects. These thermal effects include increased blood flow, a reduction of stiffness and spasm, an increase in flexibility of tendon and joint capsules, and decreased pain. Pulsed waves typically produce non-thermal effects. These effects include tissue regeneration, collagen synthesis, an increase in blood flow, and a reduction of edema, an excess of fluid which causes swelling.