Heat as a therapeutic modality in physiotherapy has been used many years and is divided in two categories: superficial and deep heating agents. Deep heating modalities include therapeutic longwave and shortwave diathermy, ultrasound and TECAR therapy. This kind of deep heat therapy is known and described as Diathermy.

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" (adj., diather´mal, diather´mic). The earliest observations on the reactions of high-frequency electromagnetic currents upon the human organism were made by Jacques Arsene d'Arsonval (1890-1891). 

The primary physiological effects and benefits of using diathermy include: increased circulation and blood flow, increased metabolism, increased muscle temperature, increased tissue temperature, decreased pain, decreased tissue stiffness and muscle spasm relaxation. A therapist using diathermy in physiotherapeutical care may take advantage of these primary physiological effects at improve inflammatory conditions, decrease pain, increase metabolic functions, increase deep tissue temperature, and increase range of motion as a direct influence on tissue. Indirect use of the primary effects of diathermy consists of administering diathermy as a part of a treatment in combination therapy with other physiotherapeutical techniques like manual therapy, exercise therapy, fascia therapy, percutaneous electrolysis and shockwave therapy.

Secondary physiological effects for diathermy are described by literature for TECAR (transfer of electric current in capacitive or resistive way), the most recent technology capable of producing a diathermal effect in human tissue. This kind of condenser based direct contact diathermy, using low frequency radio waves improve the ion exchange at cellular level. Thus creating an accelerated healing response.

Scientific literature teaches us that diathermy administered by a skilled therapist may be of great value in achieving good results as a primary therapeutical strategy or as part of a combined treatment plan.

Source: Gymna. What is Diathermy. https://gymna.com/en/stories/what-diathermy (ND)