Which muscle initiates abduction of the arm?

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Multiple Choice

Which muscle initiates abduction of the arm?

Explanation:
Supraspinatus starts the motion of lifting the arm. This rotator cuff muscle sits in the supraspinous fossa, passes beneath the acromion, and inserts on the superior facet of the greater tubercle of the humerus. When it contracts, it pulls the humeral head into the glenoid and begins abduction through the first roughly 15 degrees, while also stabilizing the head to prevent superior migration. After this initial phase, the deltoid becomes the main elevator for continued abduction. The other rotator cuff muscles primarily stabilize and rotate rather than initiate abduction. The supraspinatus is innervated by the suprascapular nerve.

Supraspinatus starts the motion of lifting the arm. This rotator cuff muscle sits in the supraspinous fossa, passes beneath the acromion, and inserts on the superior facet of the greater tubercle of the humerus. When it contracts, it pulls the humeral head into the glenoid and begins abduction through the first roughly 15 degrees, while also stabilizing the head to prevent superior migration. After this initial phase, the deltoid becomes the main elevator for continued abduction. The other rotator cuff muscles primarily stabilize and rotate rather than initiate abduction. The supraspinatus is innervated by the suprascapular nerve.

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