Shoulder Joint Muscles. - Townsville Massage

Shoulder Joint Muscles.

The shoulder joint is one of the body’s most flexible and allows the arm to be positioned and moved in just about any direction.

The Shoulder Joint also allows the arm to be rotated inward (internal rotation) or outward (external rotation) to help put the bent forearm in a favorable position to perform a required task.

The head of the Humerus is almost spherical in shape and rotates freely in the glenoid fossa of the Scapula.
The shoulder joint’s flexible ligaments, the Rotator Cuff, and the other muscles that cross this joint all add to the shoulder’s stability and its incredibly amazing range of movement.


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.

• Anterior portion – Shoulder flexion and internal rotation.
• Posterior portion – Shoulder extension and external rotation.
• All fibres – Shoulder abduction.

Typical Use:
• Lifting.



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.

• Abduction .
• Stabilisation of the humerus and shoulder joint.

Typical use:
• Holding shopping bags away from the body


The Infraspinatus muscle assists the lifting of the arm while turning the arm outward (external rotation). It is the main external rotator of the shoulder joint.

It is one of the four rotator cuff muscles crossing the shoulder joint and is commonly injured.

• Shoulder abduction.
• External rotation.
• Stabilises the shoulder joint

Typical use:
• Brushing hair.

Teres-MajorTeres Major.

The Teres Major is only functional when the Rhomboids fix the scapula. This muscle mainly helps the Latissimus Dorsi.


• Medially rotates and adducts arm.
• Stabilises the shoulder joint.

Typical use:
• Tucking your shirt into the back of your jeans.

Teres-MinorTeres Minor.

The Teres Minor is one of the four rotator cuff muscles surrounding the shoulder. Its main action, along with the Infraspinatus  is to externally rotate the shoulder joint. It assists the lifting of the arm during outward turning (external rotation) of the arm.

There are two Teres muscles, the other being Teres Major.
The other muscles whose tendons form the rotator cuff are:
•    The infraspinatus muscle, which (like the teres minor) helps in the outward turning (external rotation) of the arm.
•    The supraspinatus muscle which is responsible for elevating the arm and moving it away from the body; and
•    The subscapularis muscle, which moves the arm by turning it inward (internal rotation).

•    External rotation.
•    Shoulder abduction and stabilises shoulder joint.

Typical use:
•    Brushing hair.


The Subscapularis moves the arm by turning it inward (internal rotation).

The 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.

“Subscapularis” means under (sub) the scapula (the wingbone). The subscapularis muscle originates there, beneath the scapula.

• Internal rotation.
• Adduction.
• Stabilises shoulder joint.

Typical use:
• Tucking your shirt into the back of your jeans.

Larissimus-DorsiLatissimus 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 and its basic function is to pull the shoulders downward and towards the back.

It extends from the spine, hip and ribs to the upper arm.

They are commonly known at ‘the lats’.

• Extends, adducts and medially rotates arm.
• Helps with deep inspiration and forced expiration

Typical use:
• Pushing down on the arms of a chair when standing up.

Pectoralis-MajorPectoralis 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 push-up exercises are good for the Pectoralis major.

• Clavicular head:flexes and adducts arm.
• Sternal head: adducts and medially rotates arm .
• Accessory for inspiration.

Typical use:
• Applying a roll-on deoderant.