Shoulder Muscles

What are shoulder muscles?

The shoulder muscles are a set of complex muscles that act as a link between the torso and the head or neck. It includes a range of muscles such as the finer stabilizer, prime mover and fixator muscles. The muscles shield a ball and socket joint which is the most freely moveable joint in the body.

Image Source: en.wikipedia.org

Following are the various parts that make up the shoulder muscles:

Front View of shoulder muscles

• Deltoid (anterior head): Helps in internal rotation by allowing the individual to rotate the upper arm inwards and in flexing it forward Image Source: en.wikipedia.org
• Pectoralis minor: Aids in drawing the shoulder blade upward and downward Image Source: en.wikipedia.org
• Coracobrachialis: The muscle enables the upper arm to flex in the forward direction Image Source: en.wikipedia.org
• Biceps brachii: It facilitates slight flexing of the upper arm in the shoulder while it also helps in flexing and supinating the forearm Image Source: en.wikipedia.org
• Subclavius: Provides depression in the lateral part of the clavicle Image Source: en.wikipedia.org

Back View of shoulder muscles

• Trapezius: Brings the shoulder blades together by retraction and enables elevation and depression of the shoulder Image Source: en.wikipedia.org
• Deltoid (posterior and middle head): Helps in the sideways movement of the upper arm known as abduction, bringing it closer to the body known as adduction and extending it backward for external rotation.
• Latissimus dorsi: Allows extension and medial rotation of the arm Image Source: en.wikipedia.org
• Rotator cuff muscle Helps in movement of the upper arm in the shoulder joint and has the following parts:
  – Subscapularis: Internal rotation of the upper arm
  – Supraspinatus: Abduction or sideways movement of the upper arm
  – Infraspinatus: External rotation of the upper arm
  – Teres minor: Moves the upper arm towards the body through abduction
  Image Source: en.wikipedia.org
• Levator scapulae: Aids in elevation of the shoulder blade Image Source: en.wikipedia.org
• Teres major: Helps in backward extension and internal rotation of the upper arm Image Source: en.wikipedia.org
• Rhomboid major and minor: Retraction of the shoulder blades Rhomboid Major Muscle. Image Source: en.wikipedia.org Rhomboid Minor Muscle. Image Source: en.wikipedia.org

   

• Serratus anterior: Facilitates protraction or moving apart of the shoulder blades Image Source: en.wikipedia.org
• Triceps branch: Adduction or backward extension of the upper arm, moving it towards the body Image Source: en.wikipedia.org

Functions of the shoulder muscles:

 

Muscles involved	Function
Anterior deltoid, biceps brachii, pectoralis major, coracobrachialis	Moving the arm forward
Triceps brachii, posterior deltoid, teres major, latissimus dorsi	Moving an arm backward
Upper trapezius, serratus anterior, posterior & middle deltoid, supraspinatus	Abduction or lifting the arm sideways
Teres major, pectoralis minor, pectoralis major, latissimus dorsi, coracobrachialis	Adduction or moving the arm closer to the body
Anterior deltoid, pectoralis major	Horizontal adduction or medial movement of the arm from a horizontal front position
Infraspinatus, posterior deltoid, teres minor	External lateral rotation – arm flexes with the elbow toward the body
Subscapularis, teres major, anterior deltoid, latissimus dorsi, pectoralis major	Internal medial rotation – arm flexes with the elbow moving away from the body
Lower trapezius, Pectoralis minor, Latissimus dorsi, Subclavius	Depression of the shoulder or scapular depression
Pectoralis minor	Scapular tilt – forward movement of the upper part of the scapula
Serratus anterior, trapezius	Moving the lateral angle of the scapular upward or scapular upward rotation
Pectoralis major, Pectoralis minor, Subclavius, Latissimus dorsi	Scapular downward rotation or moving the lateral angle of the scapula downward
Rhomboideus major and minor, Trapezius	Scapular adduction or retraction – bringing the shoulder blades closer by moving the shoulders backward
Serratus anterior, Pectoralis major, Pectoralis minor	Bringing the shoulders forward – scapular protraction or abduction