THE MOTOFACIENT AND NONMOTOFACIENT CYCLES IN ELEVATION OF THE HUMERUS

Abstract

The generally accepted view that in raising the humerus to a straight angle, the deltoid elevates the arm approximately to a right angle, after which elevation is completed by scapular rotation, is not supported by our investigation. The deltoid alone is unable to raise the humerus beyond 60 degrees while elevation from this to approximately 115 degrees involves scapular rotation, after which the deltoid again becomes active and completes the elevation. Inspection and palpation or electrical stimulation of the deltoid will verify the active role it plays in elevation of the arm from 115 degrees to a straight angle. The deltoid acts first as an abductor, abducting the arm approximately 60 degrees, and then after elevation to 115 degrees it becomes an adductor, thereby raising the arm through the final arc to 180 degrees. The origin and insertion of the deltoid are so placed that it may serve this dual