When applying ultrasound for lateral epicondylitis, the factor LEAST dependent on heat absorption is:

In ultrasound therapy, particularly for conditions such as lateral epicondylitis, heat absorption is influenced by various factors, including intensity, duration of exposure, and the size of the area being treated.

The choice of coupling agent is indeed the factor least dependent on heat absorption. Coupling agents, such as gels or oils, primarily serve to facilitate the transmission of ultrasound waves from the transducer to the skin by eliminating air pockets that hinder the effective delivery of ultrasound energy. While different coupling agents may affect the efficiency of transmission to some extent, they do not significantly impact the amount of heat generated or absorbed by the tissues during the ultrasound application.

In contrast, intensity directly relates to the power of the ultrasound waves, which affects the degree of heat produced in the tissues. The duration of exposure also plays a crucial role; longer application times can increase the temperature within the tissues. The size of the area sonated is significant because larger areas require careful consideration of the energy delivered to ensure adequate heating without overheating small, localized spots.

Thus, while the choice of coupling agent is important for effective ultrasound delivery, it does not primarily determine the heat absorption characteristics in the context of ultrasound treatment for lateral epicondylitis.