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Shoulder Muscles Chapter 5 Determination of Muscle Action 1. Muscle location? Origin and insertion 2. What joint(s) it crosses or act on? Where does the muscle cross the joint? (e.g. anterior, lateral, etc.) 3. What are the possible planes of movement and actions at that joint? (also see pages 23, 24) 4. What is the line of pull? Muscles only pull on bones, they do not push bones. Insertion is usually pulled towards the origin. Remember, most muscle can not perform opposite actions (e.g. flexion AND extension). Anterior Muscles • Coracobrachialis • Pectoralis major • Subscapularis Coracobrachialis • Origin: coracoid process • Insertion: medial humerus • Actions: • Horizontal Adduction of the shoulder • flexion of the shoulder • adduction of the shoulder Pectoralis Major • • • Origin: • Proximal clavical (clavicular head) • Sternum (sternal head) Insertion: Intertubercular groove Actions: • Clavicular (upper) • Internal rotation • Horizontal adduction • Flexion up to 60º • Adduction beyond 90º • Abduction below 90º • Sternal (lower) • Internal rotation • Horizontal adduction • Extension to a neutral position • Adduction • Pectoralis Major Subscapularis • Origin: subscapular fossa • Insertion: lesser tubercle • Actions: • Internal rotation • Adduction • Extension • Other: anterior rotator cuff muscle Note: Anterior view. The ribs are removed from this image Superior Muscles • Deltoid • Supraspinatus Deltoid • Origin: • Anterior: distal clavicle • Middle: acromion process • Posterior: spine of scapula • Insertion: • Actions • Anterior: abduction, flexion, internal rotation, horizontal adduction • Middle: abduction • Posterior: abduction, extension, external rotation, horizontal abduction • Deltoid Lateral view Supraspinatus • Origin: supraspinatus fossa • Insertion: greater tubercle • Action: abduction • Other: rotator cuff muscle Inferior Muscles • Latissimus dorsi • Teres major Latissimus Dorsi • Origin: • Insertion: intertubercular groove • Actions: • adduction • internal rotation • extension • horizontal abduction • “swimmer’s muscle” Teres Major • Origin: inferior angle • Insertion: intertubercular groove • Actions: • adduction • internal rotation • extension “lats little helper” Posterior Muscles • Infraspinatus • Teres minor Infraspinatus • Origin: infraspinus fossa • Insertion: greater tubercle • Actions: • extension • external rotation • horizontal abduction • Other: rotator cuff muscle Teres Minor • Origin: lateral border • Insertion: greater tubercle • Actions: • extension • external rotation • horizontal abduction • Other: rotator cuff Rotator Cuff Muscles S.I.T.S • Name the horizontal adduction muscles • pectoralis major (upper and lower fibers) • corachobrachialis • anterior deltoid • Name the horizontal abduction muscles • posterior deltoid • infraspinatus • teres minor • latissimus dorsi • Name the flexor muscles • coracobrachialis • pect major (upper fibers) • anterior deltoid • Name the extensor muscles • latissimus dorsi • teres major • posterior deltoid • pectoralis major (lower fibers) • Name the adductor muscles • pect major (upper and lower fibers) • coracobrachialis • latissimus dorsi • teres major • Name the abductor muscles • deltoid (all fibers) • supraspinatus • Name the internal rotator muscles • subscapularis • latissimus dorsi • teres major • anterior deltoid
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