Unless used correctly ultrasound treatment can do a lot of damage and is not recommended for amateur use. However another system that uses the same principle is infrasound, which operate at a much lower frequency than ultrasound. The units have the appearence of a simple massager, and are safe and easy to use, and after using one for several years for arthritic joints, and often on stiff, painful muscles, the one I have is remarkably effective. The best known make is Nova Sonic, but I use the Boots clone, which is identical to the Nova Sonic but a lot less expensive to buy.