External Rotation
External rotation, also called lateral rotation, is rotation away from the body.
In pitching, external rotation usually refers to the lateral rotation of the arm where the axis of rotation is the length of the humerus. In the delivery, this resembles backwards or reverse rotation of the forearm and is sometimes called "forearm lay back."
The deltoid, infraspinatus, and teres minor are muscles used for active external rotation.
Passive external rotation can occur as an inertial continuation of active external rotation and as an inertial reaction to the body's forward acceleration of the shoulder and elbow during a pitch.
See also: internal rotation.
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