Which of the following is a characteristic of superficial heating agents?

Superficial heating agents are designed to increase the temperature of the tissues closest to the surface of the skin, typically to a depth of about 1-3 cm. This characteristic is fundamental to their function, as they primarily aim to improve local circulation, enhance tissue extensibility, and facilitate the healing process by targeting superficial structures. By focusing on the upper layers of tissue, superficial heating agents can effectively warm the area to alleviate pain and increase flexibility in the skin and underlying superficial tissues.

The other characteristics associated with superficial heating agents do not accurately describe their function. For example, while some forms of heat therapy can affect deeper tissues indirectly, superficial heating agents do not deeply penetrate muscle layers effectively. They also do not solely affect surface temperature, as they do induce a degree of heat that can be felt deeper within the tissue, just not to the extent that would be required to significantly change deeper muscle layers. Additionally, superficial heating agents can still be beneficial during different stages of tissue healing, including the remodeling stage, which contradicts the notion that they are ineffective at that time.