Diathermy is the controlled production of “deep heating” beneath the skin in the subcutaneous tissues, deep muscles and joints for therapeutic purposes. Diathermy is a therapy that uses shortwaves to penetrate into damaged tissues below the surface to increase elasticity of damaged soft tissues. At Hall Chiropractic we use it to treat musculoskeletal pain, swelling, chronic back pain. It also acts to increase blood flow, decreasing pain and speeding up the healing process.
From AltMD: The therapeutic effects of heat have long been recognized. More than 2,000 years ago, the Romans took advantage of heat therapies by building hot-spring bathhouses. Since then, various methods of using heat have evolved. In the early 1890s, French physiologist Arséne d’Arsonval began studying the medical application of high-frequency currents. The term diathermy was coined by German physician Carl Franz Nagelschmidt, who designed a prototype apparatus in 1906. Around 1925, United States doctor J. W. Schereschewsky began studying the physiological effects of high-frequency electrical currents on animals. It was several years, however, before the fundamentals of the therapy were understood and put into practice. Ref. AltMD
http://www.altmd.com/Articles/Diathermy–Encyclopedia-of-Alternative-Medicine