Which statement correctly describes how shoulder abduction is initiated?

Which statement correctly describes how shoulder abduction is initiated?

• A. Deltoid (middle) initiates abduction.
• B. Infraspinatus initiates.
• C. Supraspinatus initiates abduction.
• D. Supraspinatus initiates abduction, with the middle deltoid becoming primary after.

Answer: (D)

Shoulder abduction starts with the supraspinatus. This rotator cuff muscle gently pulls the humeral head into the glenoid and begins lifting the arm from rest, roughly during the first 0 to 15 degrees of elevation. It also helps stabilize the joint as the deltoid starts to contract. After about 15 degrees, the middle deltoid becomes the primary elevator to continue abduction, while the supraspinatus still assists and keeps the humeral head centered. The infraspinatus isn’t the initiator; its main role is external rotation. For full overhead lift, the scapula must rotate via trapezius and serratus anterior to allow more elevation. So, the statement that initiation is by the supraspinatus, with the middle deltoid taking over afterward, best captures how abduction is controlled.

Shoulder abduction starts with the supraspinatus. This rotator cuff muscle gently pulls the humeral head into the glenoid and begins lifting the arm from rest, roughly during the first 0 to 15 degrees of elevation. It also helps stabilize the joint as the deltoid starts to contract. After about 15 degrees, the middle deltoid becomes the primary elevator to continue abduction, while the supraspinatus still assists and keeps the humeral head centered. The infraspinatus isn’t the initiator; its main role is external rotation. For full overhead lift, the scapula must rotate via trapezius and serratus anterior to allow more elevation. So, the statement that initiation is by the supraspinatus, with the middle deltoid taking over afterward, best captures how abduction is controlled.