When instructed to lie on your stomach, what movement are you performing?

The act of lying on your stomach is specifically referred to as "pronation." In anatomical terms, pronation describes the rotation or movement that turns a body part downward or forward. When you lie face down, your body is in a prone position, meaning your torso and face are oriented towards the ground.

In this position, the anatomical alignment involves the rotation of the body around the axis created by the spine, which is indicative of pronation. This term is often used in relation to the forearm as well, where pronation means turning the palm downward.

Other terms such as flexion and extension refer to bending and straightening movements at joints, while supination is the opposite of pronation, indicating a rotation that turns a body part upwards. Thus, choosing pronation accurately describes the movement involved in lying on your stomach.