Which of the following is a deep heating modality?

• A. Ultrasound
• B. Hot packs
• C. Paraffin
• D. Fluidotherapy

Answer: (A)

Deep heating modalities are those that raise tissue temperature beyond the superficial layers, reaching deeper structures such as muscle and tendon. Ultrasound does this by sending high-frequency sound waves into the body; the waves travel through tissues and are absorbed, converting the energy into heat. When used with a continuous duty cycle, this heating can penetrate to deeper tissues, with depth influenced by the frequency chosen (lower frequencies reach deeper tissues, higher frequencies stay more superficial). This makes ultrasound a classic deep heating modality because it can elevate temperature well below the skin surface to help with tissue extensibility, pain relief, and circulation.

In contrast, hot packs, paraffin, and fluidotherapy primarily heat the surface, or just beneath the surface, through conduction or convection. They warm the skin and superficial layers rather than penetrating deeply, so their heating effect is mainly superficial rather than deep.