From 15-90 degrees, the arm is abducted by the Deltoid muscle. From 90-180 degrees, the arm as abducted by the Trapezius muscle with help from the Serratus Anterior muscle. Abduction of the arm occurs in three segments, and hence is performed by three different sets of muscles. From 0-15 degrees, the arm is abducted by the Supraspinatus muscle. From 15-90 degrees, the arm is abducted by the Deltoid muscle.