Which statement best describes heating depth as frequency increases?

• A. Higher frequency yields more superficial heating
• B. Higher frequency yields deeper heating
• C. Frequency does not affect heating depth
• D. Lower frequency yields no heating

Answer: (A)

Heating depth in energy-based therapies depends on how quickly energy is absorbed as it moves through tissue. When frequency is higher, tissues absorb energy more rapidly, so most heating occurs near the surface. Lower frequency means energy travels farther before being absorbed, producing deeper heating. So, higher frequency yields more superficial heating. For example, ultrasound at a higher frequency tends to heat superficial layers, while a lower frequency can reach deeper muscles. The other statements don’t fit: higher frequency does not produce deeper heating; frequency does affect depth; and there is heating at lower frequencies, just at greater depths.