Final answer:
The forearm facing down indicates pronation, where the palm is turned backward. This movement is associated with actions requiring the palm facing down.
Step-by-step explanation:
The signal of the forearm facing down is related to the movements of pronation and supination which involve the rotation of the forearm and wrist. Pronation is the motion that moves the palm from a palm forward (supinated) position to a palm backward (pronated) position.
This motion is controlled by the muscles in both the superficial anterior compartment of the forearm, which are responsible for bending the wrist toward the body and tilting the hand to the side away from the body, and the superficial posterior compartment of the forearm.
It works to straighten the wrist and tilt the hand to the side away from the body. When the forearm is pronated and facing down, it is typically in a position to perform tasks that require the palm to be directed downwards, like typing on a keyboard or pushing down on a surface.