Shoulder MusclesChapter 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?

1. 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

• Deltoid

• Supraspinatus

Superior Muscles

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

• Origin: supraspinatus fossa

• Insertion: greater tubercle

• Action: abduction

• Other: rotator cuff muscle

Supraspinatus

Inferior Muscles

• Latissimus dorsi

• Teres major

• Origin:• Insertion: intertubercular groove• Actions:

• adduction• internal rotation• extension• horizontal abduction

• “swimmer’s muscle”

Latissimus Dorsi

• Origin: inferior angle

• Insertion: intertubercular groove

• Actions:

• adduction

• internal rotation

• extension

Teres Major

“lats little helper”

• Infraspinatus

• Teres minor

Posterior Muscles

Infraspinatus

• Origin: infraspinus fossa

• Insertion: greater tubercle

• Actions:

• extension

• external rotation

• horizontal abduction

• Other: rotator cuff muscle

• Origin: lateral border

• Insertion: greater tubercle

• Actions:

• extension

• external rotation

• horizontal abduction

• Other: rotator cuff

Teres Minor

S.I.T.S

Rotator Cuff Muscles

• 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