Where is the Deltoid Muscle? - Location, Regions & Parts

Instructor: Alexandra Unfried

Alexandra earned her master's degree in nursing education and is currently a hospital supervisor/administrator.

The deltoid muscle plays an important role in how the arms are moved. This lesson will discuss where the deltoid muscle is located including its region and parts.

Why is it Difficult to Move my Arm?

Jessica has just finished moving from her apartment to her new house. She carried a lot of boxes during the move. Jessica is now noticing that she is having trouble raising her right arm and she is feeling pain at the top of her arm and shoulder. Jessica thinks that she may have injured her deltoid muscle and is curious how it will affect her.

Deltoid Muscle: Definition

The deltoid muscle is responsible for major movements of the arm such as rotation, the swinging of the arms back and forth, and the raising and lowering the arms. It aids in lifting objects and carrying them safely, as well as protects the shoulder from dislocation during movement.

Since Jessica carried a lot of boxes while moving she has overworked her arms and shoulders. She specifically used her deltoid muscles, which helped protect her shoulders and rotator cuffs. However, they are now very sore and it hurts to move her arms.

Deltoid Muscles: Location

The deltoid muscle is located in the upper arms and shoulders on each side of the body. It is triangular in shape with the widest part of the muscle at the shoulder and the thinnest part resting at the upper arm. A common movement of the arm that involves the action of the deltoid muscle is raising the arm upward from a resting position at the side of the body. A distinct contraction can be felt where the shoulder meets the arm.

Location of the deltoid muscle

Deltoid Muscles: Region

The deltoid muscle is attached at three points on each side of the body. These include:

  • Outer end on the clavicle (collar bone)
  • Acromion process of the scapula (bony process on the shoulder blade)
  • Spine of the scapula (bony prominence on the back of the shoulder blade)

Each area of attachment contains its own set of muscle fibers. The anterior fibers form at the clavicle, the lateral (middle) fibers form at the acromion process of the scapula, and the posterior fibers form at the spine of the scapula. These three fibers come together at the humerus bone located at the upper arm.

The clavicle and scapula where the deltoid muscle attaches

Jessica feels pain in her upper arm and shoulder because she used her deltoid muscles while lifting heavy objects. The muscles and fibers are tired and sore.

Deltoid Muscle: Parts

As mentioned above, the three parts of the deltoid are distinct muscle fibers making up the anterior deltoid, lateral deltoid, and posterior deltoid. Each of these parts is responsible for different types of arm movement.

  • Anterior deltoid: reaching forward or lifting the arm in front of the body
  • Lateral deltoid: reaching out to the side of the body
  • Posterior deltoid: reaching backwards or behind the body

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