Question

which muscles are primarily responsible for the first phase (0 to 90 degrees) of shoulder abduction?
serratus anterior and trapezius
deltoid and supraspinatus
pectoralis major and latissimus dorsi
infraspinatus and teres minor

Explanation:

The first 0-90 degrees of shoulder abduction relies on the supraspinatus to initiate the movement, with the deltoid (middle fibers) providing the primary force to lift the arm to 90 degrees. Other options control different shoulder motions: serratus anterior/trapezius stabilize the scapula, pectoralis major/latissimus dorsi handle adduction/extension, and infraspinatus/teres minor manage external rotation.

Answer:

Deltoid and supraspinatus