Ultrasound has it's origins in the United States Military when it was used as SONAR (Sound Navigation And Ranging). These early forms of ultrasound were used on submarines where it was noticed that, all of a sudden, the fish and underwater life in that area were dead! The ultrasound was heating the water and baking everything in the area. This phenomenon was researched for its potential clinical applications and the ultrasound machine was born! Ultrasound can now be used to either visualize structures in the body (diagnostic) or to heat tissues within the body at various depths (therapeutic) by emitting high-frequency sound waves. Don't worry, it is set to an intensity that won't kill you! These advances allow ultrasond to be used for safe, non-invasive imaging of structures in the body, as a biofeedback tool to facilitate muscle activation, guiding needle placements, internally heating tendons and other structures, and even for healing fractures and some open wounds!