Supination is a term used to describe a type of rotation involving the hand or the foot. When the term is applied to the hand, it describes the movement of the arm and hand that results in an upward-facing palm. When applied to the foot, the term refers to movement that results in the upward positioning of the sole of the foot.
Pronation and supination are a pair of unique movements possible only in the forearms and hands, allowing the human body to flip the palm either face up or face down.
Proper functioning of the hand relies on its capacity to rotate and point the palm upward (i.e. supination) or downward (i.e. pronation) when standing up with the elbow in 90° flexion. Hand rotation is possible because of forearm rotation and also rotation of the whole upper limb at the shoulder.This diagram with labels depicts and explains the details of Supination Of Hand.