Which term refers to the action of turning the palms of the hands downward?

The term that describes the action of turning the palms of the hands downward is "pronator." This movement is characterized by the rotation of the forearm in such a manner that the palm faces downwards or backward. Pronators are muscles that facilitate this specific motion, effectively opposing the action of muscles that would turn the palm upward, known as supinators.

In contrast, the terms "flexor" and "extensor" refer to different types of muscle actions involving bending (flexion) or straightening (extension) a joint. Therefore, they are not relevant to the action of turning the palms downward. Similarly, the term "supinator" describes the opposite movement where the palm is turned upward. Understanding these terms is crucial for accurately describing movements in anatomy and exercise physiology.