Which muscle abducts the shoulder when all parts act together?

Which muscle abducts the shoulder when all parts act together?

• A. Deltoid
• B. Supraspinatus
• C. Infraspinatus
• D. Latissimus Dorsi

Answer: (A)

Abduction of the shoulder is produced mainly by the deltoid, especially the middle fibers, which lift the arm away from the body once the movement has begun. The supraspinatus starts the act and keeps the humeral head centered, but when all parts are working together, the deltoid does the bulk of the lifting. The other muscles listed don’t serve as the primary abductors: the infraspinatus mainly externally rotates and stabilizes the shoulder, while latissimus dorsi pulls the arm downward and inward (adduction and internal rotation). So the deltoid is the best answer for the muscle that abducts the shoulder when all parts act together.

Abduction of the shoulder is produced mainly by the deltoid, especially the middle fibers, which lift the arm away from the body once the movement has begun. The supraspinatus starts the act and keeps the humeral head centered, but when all parts are working together, the deltoid does the bulk of the lifting. The other muscles listed don’t serve as the primary abductors: the infraspinatus mainly externally rotates and stabilizes the shoulder, while latissimus dorsi pulls the arm downward and inward (adduction and internal rotation). So the deltoid is the best answer for the muscle that abducts the shoulder when all parts act together.