muscles acting on the arm

supraspinatus

• abduction of arm

• resists downward slippage of humeral head when arm is relaxed or carrying weight

infraspinatus

• lateral rotation of arm

• resists upward slippage of humeral head

teres minor

• abduction and lateral rotation of arm

• resists upward slippage of humeral head when arm is abducted

subscapularis

• medial rotation of arm

• resists upward slippage of humeral head when arm is abducted

deltoid

• anterior fibers

  • medial rotation of arm

  • shoulder flexion

• lateral fibers

  • arm abduction

• posterior fibers

  • shoulder extension

• arm swinging in such actions as walking and bowling

• adjustment of hand height for manual tasks

teres major

• medial rotation of arm

• shoulder extension

• arm swinging during walking

coracobrachialis

• medial rotation of humerus

• shoulder flexion

• resists deviation of arm from frontal plane during abduction

pectoralis major

• medial rotation and adduction of arm

• shoulder flexion, as in climbing or hugging

• assistance in deep breathing

latissimus dorsi

• medial rotation and adduction of arm

• shoulder extension, as in pulling on oars of a rowboat

• backswing of arm as in walking or bowling

• strong downstrokes of arm as in hammering and swimming

• assistance in deep inhalation, sudden exhalation as in sneezing and coughing, and prolonged forceful exhalation as in singing or playing a wind instrument

• with hands grasping overhead objects, pulls body forward and upward as in climbing