Final answer:
Diathermy is a physical therapy modality that uses high-intensity ultrasound or microwaves to produce deep heating in tissue. It is used to relieve pain and improve flexibility in injured or overworked muscles. Skilled application is required to avoid tissue damage.
Step-by-step explanation:
Diathermy is a physical therapy modality that uses high-intensity ultrasound or microwaves to produce deep heating in tissue. When ultrasound diathermy is used, most of the energy is converted to thermal energy, which helps to relieve pain and improve flexibility in injured or overworked muscles. However, it requires skilled application by a therapist to avoid tissue damage caused by overheating. Microwave diathermy, on the other hand, is used for treating muscular pains, spasms, tendonitis, and rheumatoid arthritis. It penetrates deeper into tissue than shorter wavelengths and provides deep heating for therapeutic purposes.