Shoulder Joint Muscles
The muscles of the shoulder joint are those which function to move the upper arm bone.
Movements which are possible at this joint include flexion, extension, abduction, adduction,
internal and external rotation.
Shoulder joint muscles can loosely be grouped into the four rotator cuff muscles which rotate the
shoulder (Supraspinatus, Infraspinatus, Subscapularis and Teres minor) and the large global
muscles which flex, extend, adduct and abduct it (Pectoralis Major, Latissimus dorsi, Deltoid)
Supraspinatus
The Supraspinatus muscle is one of the four muscles which make up the rotator
cuff. Its main function is to stabilise the upper arm by holding the head of the
humerus in position. It is important in throwing motions to control any forward
motion of the head of humerus.
Origin

Supraspinous fossa.
Insertion

Greater tuberosity of the humerus.
Actions

Shoulder abduction.

Stabilisation of the humerus.
Innervation

Suprascapular nerve.
Daily uses

Holding shopping bags away from the body.
Example strengthening exercises

Lateral raise.

Shoulder external rotation.
Example stretches

Supraspinatus stretch.

Posterior shoulder stretch.
Related injuries

Inflammation of the supraspinatus tendon.

Rotator cuff injuries.

Impingement syndrome.
Related muscles

Infraspinatus

Subscapularis.

Teres minor.
Infraspinatus
The Infraspinatus muscle is one of the four rotator cuff muscles crossing the
shoulder joint and is commonly injured. It is the main external rotator of the
shoulder joint.
Origin

Posterior surface of the scapula (below the spine of the scapula).
Insertion

Greater tuberosity on the humerus.
Actions

Shoulder abduction

External rotation.
Innervation

Suprascapular nerve.
Daily uses

Brushing hair.
Example strengthening exercises

Lateral raise.

Shoulder external (lateral) rotation.
Example stretches

Internal rotation stretch.

Posterior shoulder stretch.
Related injuries

Rotator cuff injury.

Impingement syndrome.
Related muscles

Supraspinatus.

Subscapularis.

Teres minor.
Subscapularis
Subscapularis is one of the four rotator cuff muscles which cross the shoulder
joint. The muscle also acts to hold the head of the humerus in position and
prevents it moving forwards. It is shown here with a couple of ribs cut away at the
front.
Origin

Anterior (costal) surface of the scapula.
Insertion

Lesser tuberosity of the humerus.
Actions

Internal rotation.

Adduction.
Innervation

Upper and lower subscapular nerves.
Daily uses

Tucking the back of your shirt into your trousers.
Example strengthening exercises

Diagonal extension.
Example stretches

External rotation stretch.
Related injuries

Inflammation of the subscapularis muscle.

Rotator cuff injuries.
Related muscles

Supraspinatus.

Infraspinatus.

Teres minor.
Teres Minor
Teres Minor is one of the four rotator cuff muscles surrounding the shoulder. Its
main action, along with Infraspinatus is to externally rotate the shoulder joint.
There are two Teres muscles, the other being Teres Major.
Origin

Mid section of the lateral border of the scapula.
Insertion

Greater tuberosity on the humerus.
Actions

External rotation.

Shoulder adduction.
Innervation

Axillary nerve.
Daily uses

Brushing hair.
Example strengthening exercises

Shoulder external rotation.
Example stretches

Internal rotation stretch.
Related injuries

Rotator cuff injuries.
Related muscles

Supraspinatus.

Infraspinatus.

Subscapularis.

Teres major.
Deltoid
The deltoid muscle is used in all side lifting movements and any movement of the
humerus on the scapula. It is divided into three portions, anterior, middle and
posterior, with the fibres having different roles due to their orientation.
Origin

Outer 1/3 of the clavicle

Acromion process

Spine of the scapula
Insertion

Deltoid tuberosity on the humerus
Actions

Anterior portion - Shoulder flexion and internal rotation

Posterior portion - Shoulder extension and external rotation

All fibres - Shoulder abduction
Innervation

Axillary nerve
Daily uses

Lifting
Example stretches

Anterior shoulder stretch

Posterior shoulder stretch
Example strengthening exercises

Lateral raise

Front raise
Related injuries

Deltoid strain
Related muscles

Infraspinatus

Supraspinatus
Pectoralis Major
Pectoralis major is the largest and most superficial of the two chest muscles. Pec
major and the anterior fibres of Deltoid work closely together. Pec-fly and pushup exercises work the Pectoralis major.
Origin

Medial 1/2 of the clavicle.

Costal cartilages of the first 6 ribs.

Sternum.
Insertion

Intertubercular groove (between the greater and lesser tubercles) of the humerus.
Actions

Shoulder flexion.

Internal rotation.

Adduction.
Innervation

Lateral and medial pectoral nerves.
Daily uses

Using roll-on deodorant.
Example strengthening exercises

Pec fly using a resistance band.

Chest Press using a resistance band.
Example stretches

Chest stretch.

Chest stretch with a partner.
Related injuries

Pectoral strain.
Related muscles

Pectoralis minor.
Latissimus Dorsi
The Latissimus dorsi muscle is one of the largest in the body. It is a powerful
extensor muscle of the arm and is used extensively in chinning and climbing.
They are commonly known at the lats.
Origin

Posterior crest of the ilium (via the Thoracolumbar fascia).

Posterior sacrum.

Spinous processes of T7-L5.
Insertion

Intertubercular groove (between the greater and lesser tuberosities) of the humerus.
Actions

Shoulder extension.

Internal rotation.

Adduction.
Innervation

Thoracodorsal nerve.
Daily uses

Pushing on the arms of a chair when standing up.
Example strengthening exercises

Lat pull down using a resistance band.
Example stretches

Latissimus dorsi stretch I.

Latissimus dorsi stretch II.
Related injuries

Tight muscles in the upper back and neck.
Related muscles

Teres major.
Teres Major
Teres major is only functional when the Rhomboids fix the scapula. This muscle
mainly helps Latissimus dorsi.
Origin

Lower 1/3 of the lateral border of the scapula.
Insertion

Intertubercular goove (between the greater and lesser tubercles) of the humerus.
Actions

Shoulder adduction

Internal rotation

Shoulder extension.
Innervation

Lower subscapular nerve.
Daily uses

Tucking the back of your shirt into your trousers.
Example strengthening exercises

Shoulder internal rotation.
Example stretches

External rotation stretch.
Related muscles

Latissimus dorsi.

Teres minor.