<unk>  with superior limb in abduction When all its fibers contract simultaneously, the<unk>  is the prime mover of arm abduction along the frontal plane. The arm must be medially rotated for the<unk>  to have maximum effect. This makes the<unk>  an antagonist muscle of the pectoralis major and latissimus dorsi during arm adduction. The anterior fibers assist the pectoralis major to flex the shoulder. The anterior<unk>  also works in tandem with the subscapularis, pecs and lats to internally (medially) rotate the humerus. The intermediate fibers perform basic shoulder abduction when the shoulder is internally rotated, and perform shoulder transverse abduction when the shoulder is externally rotated. They are not utilized significantly during strict transverse extension (shoulder internally rotated) such as in rowing movements, which use the posterior fibers. The posterior fibers assist the latissimus dorsi to extend the shoulder. Other transverse extensors, the infraspinatus and teres minor, also work in tandem with the posterior<unk>  as external (lateral) rotators, antagonists to strong internal rotators like the pecs and lats. An important function of the<unk>  in humans is preventing the dislocation of the humeral head when a person carries heavy loads. The function of abduction also means that it would help keep carried objects a safer distance away from the thighs to avoid hitting them, as during a farmer's walk. It also ensures a precise and rapid movement of the glenohumeral joint needed for hand and arm manipulation. The intermediate fibers are in the most efficient position to perform this role, though like basic abduction movements (such as lateral raise) it is assisted by simultaneous co-contraction of anterior/posterior fibers. The<unk>  is responsible for elevating the arm in the scapular plane and its contraction in doing this also elevates the humeral head. To stop this compressing against the undersurface of the acromion the humeral head and injuring the supraspinatus tendon, there is a simultaneous contraction of some of the muscles of the rotator cuff: the infraspinatus and subscapularis primarily perform this role. In spite of this there may be still a 1–3 mm upward movement of the head of the humerus during the first 30° to 60° of arm elevation.
Deltoid muscle
Subscapularis muscle
Latissimus dorsi muscle
Achilles tendon
Pulled hamstring
Superior oblique muscle
Pectus
Dilator