For an acute injury, ultrasound should be used with what duty cycle?

• A. Low duty cycle
• B. High duty cycle
• C. 100% duty cycle
• D. No ultrasound treatment

Answer: (A)

Duty cycle is the fraction of time that the ultrasound is actively on during treatment. For an acute injury, the goal is to minimize tissue heating while still providing the mechanical effects that can aid healing. Using a pulsed ultrasound with a low duty cycle keeps the average energy delivered low, reducing the risk of overheating, edema, or inflammation, and allows non-thermal mechanisms like cavitation and acoustic streaming to support tissue repair during the on-phases. In contrast, a high duty cycle or continuous (on continuously) increases tissue temperature and can worsen acute inflammation, so they are less appropriate in the acute phase. Not using ultrasound at all would miss potential benefits, so when therapy is indicated, a low duty cycle is the best choice.