SHOULDER MUSCLES

GENERAL INFORMATION ABOUT SHOULDER MUSCLES

The shoulder muscles consist of a combination of large and small muscles responsible for the complex movements of the shoulder joint, one of the most mobile joints in the body. Shoulder muscles provide strength, stability, and range of motion, supporting various movements such as flexion, extension, abduction, adduction, and rotation. The shoulder muscles also stabilise the shoulder girdle during upper body movements, contributing to posture and overall arm function.

ORIGIN OF SHOULDER MUSCLES

• Deltoid: Lateral third of the clavicle, acromion, and spine of the scapula.

• Supraspinatus: Supraspinous fossa of the scapula.

• Infraspinatus: Infraspinous fossa of the scapula.

• Subscapularis: Subscapular fossa of the scapula.

• Teres Minor: Lateral border of the scapula.

INSERTION POINT

• Deltoid: Deltoid tuberosity of the humerus.

• Supraspinatus: Greater tubercle of the humerus.

• Infraspinatus: Greater tubercle of the humerus.

• Subscapularis: Lesser tubercle of the humerus.

• Teres Minor: Greater tubercle of the humerus.

MAJOR ARTERIES

• Posterior Circumflex Humeral Artery: Supplies the deltoid.

• Suprascapular Artery: Supplies the supraspinatus and infraspinatus.

• Subscapular Artery: Supplies the subscapularis.

• Circumflex Scapular Artery: Supplies the teres minor.

NEURAL INNERVATION

• Deltoid: Axillary nerve (C5-C6).

• Supraspinatus: Suprascapular nerve (C5-C6).

• Infraspinatus: Suprascapular nerve (C5-C6).

• Subscapularis: Upper and lower subscapular nerves (C5-C7).

• Teres Minor: Axillary nerve (C5-C6).

TRIGGER POINT

Trigger points in the shoulder muscles, particularly in the deltoid and rotator cuff, can cause sharp pain radiating to the arm, neck, or upper back. These points often develop due to repetitive overhead movements, poor posture, or muscle overuse, leading to stiffness, restricted range of motion, and discomfort during shoulder movements or rest.

CONCENTRIC FUNCTION

• Deltoid: Abducts, flexes, and extends the arm at the shoulder joint, which is critical for lifting and rotating the arm.

• Supraspinatus: Initiates abduction of the arm and stabilises the humeral head in the shoulder socket.

• Infraspinatus: Externally rotates the arm, stabilising the shoulder joint during movement.

• Subscapularis: Internally rotates the arm and helps stabilise the shoulder during upper body movements.

• Teres Minor: Assists in external rotation of the arm and stabilises the shoulder.

ECCENTRIC FUNCTION

• Deltoid: Controls the lowering of the arm during adduction, maintaining stability and smooth movement.

• Supraspinatus: Regulates the downward movement of the arm after abduction, preventing excessive joint movement.

• Infraspinatus: Controls internal rotation of the arm, ensuring smooth shoulder movements during extension.

• Subscapularis: Controls external rotation and helps maintain balance in shoulder movements.

• Teres Minor: Slows internal rotation of the arm, helping maintain stability during dynamic shoulder actions.

ISOMETRIC FUNCTION

Shoulder muscles help stabilise the shoulder joint during static positions, such as holding the arm in place during lifting or carrying. The deltoid and rotator cuff muscles work together to prevent unwanted movement and maintain shoulder alignment under tension.

RELATED MUSCLE – SCIENTIFIC NAMES

• Pectoralis Major: Assists in shoulder flexion and adduction.

• Latissimus Dorsi: Works with the shoulder muscles in extension and adduction.

• Trapezius (Upper fibres): Elevates and stabilises the scapula during shoulder movements.

• Biceps Brachii: Assists in shoulder flexion and elbow movements.

• Rhomboids: Helps stabilise and retract the scapula during shoulder actions.

ANTAGONIST

• Latissimus Dorsi: Opposes the deltoid by assisting with shoulder extension and adduction.

• Teres Major: Works against the supraspinatus by performing internal rotation and adduction.

• Subscapularis: Opposes external rotation performed by the infraspinatus and teres minor.

• Pectoralis Major: Assists in internal rotation, opposing the external rotators of the shoulder.

• Biceps Brachii (long head): Assists in shoulder flexion, opposing the extension movement performed by the deltoid and triceps.

COMMON INJURIES OF SHOULDER MUSCLES

• Rotator Cuff Tears: Tearing of one or more rotator cuff muscles, usually caused by overuse, leading to shoulder weakness and pain.

• Shoulder Impingement: Occurs when the rotator cuff tendons become irritated or inflamed, causing pain during overhead activities.

• Dislocated Shoulder: The humerus pops out of the shoulder socket, often due to trauma or extreme stretching, resulting in pain and instability.

• Frozen Shoulder (Adhesive Capsulitis): Stiffness and pain caused by inflammation and thickening of the shoulder capsule, leading to restricted movement.

• Bursitis: Inflammation of the bursa in the shoulder, often from repetitive stress or trauma, causing pain and restricted motion.

EXERCISES FOR SHOULDER MUSCLES

• Lateral Raises: Stand with dumbbells in each hand and raise your arms to shoulder height, engaging the deltoid to improve shoulder strength and stability.

• Shoulder Press: Press dumbbells or a barbell overhead, focusing on activating the deltoid and rotator cuff muscles for overall shoulder strength.

• External Rotation with Resistance Band: Attach a resistance band to a stable point and rotate the arm outward to strengthen the infraspinatus and teres minor.

• Front Raises: Hold a dumbbell in each hand and raise the arms in front of you, targeting the anterior deltoid to improve shoulder flexion strength.

• Reverse Flys: Bend at the hips and raise the arms laterally, engaging the posterior deltoid and upper back muscles for shoulder stability and posture improvement.

STRETCHES FOR SHOULDER MUSCLES

• Cross-Body Shoulder Stretch: Pull one arm across the chest using the opposite hand, stretching the posterior deltoid and rotator cuff muscles to increase flexibility.

• Doorway Chest Stretch: Stand in a doorway with the arms at shoulder height, gently pressing forward to stretch the anterior deltoid and pectoral muscles.

• Sleeper Stretch: Lie on your side, bend the top arm, and use the opposite hand to press the forearm down, stretching the infraspinatus and posterior capsule.

• Overhead Shoulder Stretch: Reach one arm overhead and gently pull the elbow with the opposite hand to stretch the deltoid and triceps.

• External Rotator Stretch: Stand and hold a towel behind your back, pulling one end upwards to stretch the external rotators, improving shoulder mobility.