Deltoid

Deltoid is a large muscle in a triangular shape that covers the shoulder joint and gives the shoulder its round shape. It is made up of three parts – the anterior (clavicular), middle (acromial), and posterior (spinal) portions. Its main functions are to move the shoulder away from the body and keep the upper arm bone stable. It also helps in lifting the arm forward.

The Deltoid muscle is very strong and is essential for everyday activities like putting on clothes, carrying bags, and washing hair, as well as in various sports like netball, swimming, and water polo.

deltoid muscle
Deltoid Anatomy

Deltoid

Anatomy

[Origin]

  • Lateral third of clavicle
  • Acromion
  • Spine of Scapula

[Insertion]

  • Deltoid Tuberosity of Humerus

[Action]

  • Clavicular part: flexes and medially rotates arm
  • Acromial part: abducts arm
  • Spinal part: extends and laterally rotates arm

Clinical Relevance

The Importance of Deltoid Muscle

All heads of the deltoid work together to produce abduction of the Shoulder Joint.  It helps lift the arm front, side, and backward. Deltoid pain can affect anyone who does repetitive overhead activities (eg. house painters, swimmers, Waterpolo players, and pitchers). It also is active with carrying objects eg suitcases or reaching up for objects, to prevent subluxation/dislocation. The deltoid compensates for the loss of strength in the rotator cuff.

Shoulder Dislocation and Deltoid Muscle

During dislocation of the shoulder or fracture of surgical neck of the humerus, axillary nerve may be injured. The damage to axillary nerve leads to paralysis of the deltoid muscle.

~ Evidence-Based Exercises ~

According to an EMG study, the exercises that demonstrated significant muscle contractions of the 3 parts of Deltoid muscle are;

  • Anterior Deltoid: Dumbbell Shoulder Press

  • Middle Deltoid: Bent-Arm Lateral Raise, 45-degree Incline Row 

  • Posterior Deltoid: Seated Rear Lateral Raise, 45-degree Incline Row

Shoulder Press

Woman shoulder press

Lateral Raises

man lateral raises

Incline Row

man dumbbell row

< Reference >