What joint movement occurs when the hand moves from a palm-up position to a palm-down position?

The movement of the hand transitioning from a palm-up position to a palm-down position is known as pronation. In anatomical terms, when the forearm is in the supinated position (palm facing up), rotating it so that the palm faces downward involves pronation. This motion is primarily facilitated by the rotation of the radius around the ulna, resulting in the palm turning in the opposite direction. Understanding this movement is essential, as it relates to various functional activities, such as typing or using tools, where hand orientation impacts grip and function.

In contrast, supination refers to the opposite movement, where the hand moves from palm-down to palm-up. Saturation does not pertain to a specific joint movement and is more associated with the degree of a solution's capability to dissolve a substance. Rotation is a broader term that might imply turning around an axis but does not specifically refer to the action of turning the palm from up to down. Therefore, pronation clearly defines the specific movement being described in the question.