Which statement about the effect of ultrasound heating on tissue properties is true?

• A. It increases tissue extensibility
• B. It causes immediate tissue necrosis
• C. It decreases blood flow
• D. It has no effect on tissue properties

Answer: (A)

Raising tissue temperature with ultrasound makes collagen-containing structures more pliable. As temperature increases, collagen cross-links loosen and tissue viscosity drops, so tendons and fascia become more extensible and stretch more easily. This is why heating is often used before stretching to improve range of motion. The other statements don’t fit therapeutic ultrasound: it doesn’t cause immediate tissue necrosis at standard settings, and heating actually increases, not decreases, blood flow due to vasodilation. It also does have an effect on tissue properties, so saying there’s no effect isn’t accurate.