Diathermy is electrically induced heat or the use of high-frequency electromagnetic currents as a form of physical or occupational therapy and in surgical procedures. The field was pioneered in 1907 by German physician Karl Franz Nagelschmidt, who coined the term diathermy from the Greek words dia and θέρμη therma, literally meaning “heating through”

This treatment is commonly used for muscle relaxation, and as a method of heating tissue electromagnetically or ultrasonically for therapeutic purposes in medicine. It is used in physical therapy and occupational therapy to deliver moderate heat directly to pathologic lesions in the deeper tissues of the body.

Diathermy is produced by three techniques: ultrasound (ultrasonic diathermy), short-wave radio frequencies in the range 1–100 MHz (shortwave diathermy) or microwaves typically in the 915 MHz or 2.45 GHz bands the methods differing mainly in their penetration capability.[1] It exerts physical effects and elicits a spectrum of physiological responses.

These procedures are good for helping the healing process with sprain/strained knees, arms, shoulders, ankles, etc. The patient may feel some warmth, but it is otherwise a painless procedure.