Realistically any therapist/physio can only work the superficial musculature of the horse by massage. Chronic muscle spasm involving a greater muscle mass must also be addressed if the horse is to remain spasm free. Unlike traditional high frequency ultrasound machines the lower frequency Orthosonics PHYS-ASSIST machine gives increased treatment penetration of 30-50cm, depth; and the use of a coupling agent is less vital. This makes it an ideal piece of equipment for use in equine work. Together with controlled exercise to work the muscles following treatment, we have a great deal of success in treating deep muscle damage and chronic sacro-iliac problems. In addition there is a non-thermal effect called acoustical steaming which refers to the movement of body fluids created by the sound wave. This is particularly marked at boundaries such as the membranes of cells and of organelles within the cells causing them to become more permeable. There is an acceleration of the rate of diffusion across the cell membranes which is important in the process of removing the debris caused by injury. This phenomenon is also useful in softening scar tissue and in increasing joint range of motion where adhesions have restricted it.