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MuscleShouldersuperficialDraft

DeltoidMusculus deltoideus

Thick, triangular muscle that caps the shoulder and is the main muscle for lifting the arm out to the side.

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LatinMusculus deltoideus
Origin
  • Anterior fibres: anterior border and upper surface of the lateral third of the clavicle
  • Middle fibres: lateral border of the acromion
  • Posterior fibres: lower lip of the spine of the scapula
Insertion
  • Deltoid tuberosity on the lateral side of the humerus shaft
Action
  • All fibres: abduct the shoulder (main abductor after the first 15° or so)
  • Anterior fibres: flex and medially rotate the shoulder
  • Middle fibres: abduct the shoulder
  • Posterior fibres: extend and laterally rotate the shoulder
  • Helps hold the head of the humerus in place when carrying heavy loads
NerveAxillary nerve (C5–C6)
NameGreek delta, the triangle-shaped letter Δ — the muscle is triangular, like an upside-down delta.

Palpation

  1. Client supine or seated; stand beside the shoulder being assessed.
  2. Place your palm over the rounded cap of the shoulder, just below the acromion, and feel the thick muscle mass.
  3. Follow the fibres down the outside of the upper arm until they narrow to a point at the deltoid tuberosity, about halfway down the humerus.
  4. Ask the client to lift the arm out to the side against light resistance to feel the middle fibres firm up.
  5. Resist forward flexion to isolate the anterior fibres, and backward extension for the posterior fibres.

Landmarks: Acromion · Spine of scapula

The deltoid is the rounded muscle that gives the shoulder its shape. It sits over the top of the rotator cuff, so in a shoulder routine you work through the deltoid first before reaching the deeper Supraspinatus and Infraspinatus. Its fibres run from the clavicle, Acromion and Spine of scapula down to a single point on the arm, so kneading and wringing work well around the cap.

Learn the three parts separately. The anterior fibres work with Pectoralis major to bring the arm forward, while the posterior fibres work with Latissimus dorsi and Teres major to take it back. This means the deltoid is partly a synergist and partly an antagonist of the pecs and lats, depending on which fibres are working.

Techniques

  • Effleurage — Long, gliding strokes with the whole palm that spread the medium, warm the tissue and link the other strokes together.
  • Petrissage — Kneading strokes that compress, lift and squeeze the muscle away from the bone, working the tissue between the hands.
  • Wringing — A petrissage stroke where the hands lift the tissue and push and pull it across the body in opposite directions, like wringing out a towel.
  • Circular friction — Small circles made with the finger or thumb pads that move the skin over the deeper tissue without sliding, to work a specific spot.
  • Compression — Pressing straight down into a muscle with the palm, fist or forearm, holding briefly, then releasing and moving on.

Works with

  • Supraspinatus — Rotator cuff muscle above the spine of the scapula that starts arm abduction and holds the head of the humerus in its socket.
  • Pectoralis major — Large, fan-shaped chest muscle that flexes, adducts and medially rotates the arm.
  • Trapezius — Large diamond-shaped muscle of the upper back and neck that moves and stabilises the scapula.
  • Serratus anterior — Saw-toothed muscle on the side of the ribcage that pulls the scapula forwards around the chest and helps rotate it upwards.

Opposes

  • Latissimus dorsi — Broad, flat, fan-shaped muscle of the lower and middle back that extends, adducts and medially rotates the arm.
  • Teres major — Thick, rounded muscle from the inferior angle of the scapula to the front of the humerus that pulls the arm down, back and inwards.

Used in routines

Sources

  1. Wikipedia: Deltoid muscle
  2. Wikipedia: Axillary nerve