Shoulder · Skeletal muscle
Deltoid (Shoulder Muscle)
The deltoid is the rounded muscle that caps the shoulder. It lifts the arm out to the side, forwards and backwards, giving the shoulder its wide range of movement.
What it is
The deltoid is a thick, triangular muscle forming the rounded contour of the shoulder, with front, middle and back parts.
Where it is
Over the top and sides of the shoulder joint.
What it does
Raises the arm out to the side, and moves it forwards and backwards; different parts act in different directions.
Everyday use
Reaching up to a shelf, lifting the arm to wave, and carrying bags all use the deltoid.
When things go wrong
Common problems affecting the deltoid (shoulder muscle)
- Deltoid strain
- Shoulder impingement (often involving nearby rotator cuff)
- Injection-site soreness (a common injection muscle)
Education and reference only. This explains the anatomy in plain terms and is not a diagnosis. Sudden severe symptoms — such as crushing chest pain or collapse — are an emergency; call 999.
Looking after it
Keeping it healthy
Good shoulder posture, rotator-cuff strength and gradual loading protect the shoulder muscles.
Did you know?
An interesting fact
The deltoid is the usual site for many vaccinations, including the flu and COVID jabs.
Answers
Deltoid (Shoulder Muscle): frequently asked questions
What does the deltoid do?
The deltoid caps the shoulder and lifts the arm out to the side, forwards and backwards, giving the shoulder its wide movement.
Why are injections given in the deltoid?
The deltoid is easy to access, has a good blood supply and is away from major nerves and vessels, making it a safe, convenient site for many vaccines.
Sources
Where this is drawn from
- NHS — Muscles and movement
- Gray's Anatomy for Students
- TeachMeAnatomy — muscular system
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