Movement (function) | Prime mover(s) (from pendent position) | Synergists | Notes |
Flexion | Pectoralis major (clavicular head); deltoid (clavicular and anterior acromial parts) | Coracobrachialis (assisted by biceps brachii) | From fully extended position to its own (coronal) plane, sternocostal head of pectoralis major is major force |
Extension | Deltoid (spinal part) | Teres major; latissimus dorsi; long head of triceps brachii | Latissimus dorsi, sternocostal head of pectoralis major, and long head of triceps act from fully flexed position to their own (coronal) planes |
Abduction | Deltoid (as a whole, but especiallly acromial part) | Supraspinatus | Supraspinatus is particularly important in initiating movement; also, upward rotation of scapula occurs throughout movement, making a significant contribution |
Adduction | Pectoralis major; latissimus dorsi | Teres major; long head of triceps brachii | In upright position and in absence of resistance, gravity is prime mover |
Medial rotation | Subscapularis | Pectoralis major; deltoid (clavicular part); latissimus dorsi; teres major | With arm elevated, "synergists" become more important than prime movers |
Lateral rotation | Infraspinatus | Teres minor; deltoid (spinal part) | |
Tensors of articular capsule (to hold head of humerus against glenoid cavity) | Subscapularis; infraspinatus (simultaneously) | Supraspinatus; teres minor | Rotator cuff (SITS) muscles acting together; when "resting", their tonus adequately maintains integrity of joint |
Resisting downward dislocation (shunt muscles) | Deltoid (as a whole) | Long head of triceps brachii; coracobrachialis; short head of biceps brachii | Used especially when carrying heavy objects (suitcases, buckets) |
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