Shoulder

The shoulder is made up of the deltoid muscles. The Deltoid is a three-headed muscle that caps the shoulder.

The three heads of the Deltoid are the Anterior Deltiod Head, Lateral Deltoid Head, and Posterior Deltoid Head.

All three Deltoid heads attach to the humerus. The Anterior and Lateral heads originate on the collar bone, while the Posterior head originates on the scapula.

The anterior fibers (head) are involved in shoulder abduction when the shoulder is externally rotated. The anterior deltoid is weak in strict transverse flexion but assists the pectoralis major during shoulder transverse flexion / shoulder flexion (elbow slightly inferior to shoulders).

The posterior fibers (head) are strongly involved in transverse extension particularly since the latissimus dorsi is very weak in strict transverse extension. The posterior deltoid is also the primary shoulder hyper extensor.

The lateral fibers (head) are involved in shoulder abduction when the shoulder is internally rotated, are involved in shoulder flexion when the shoulder is internally rotated, and are involved in shoulder transverse abduction (shoulder externally rotated) - but are not utilized significantly during strict transverse extension (shoulder internally rotated).

Exercises that work the Deltoids include:

• Seated dumbbell press,
• Bent-over laterals,
• Lateral raises,
• Military press,
• Front raises, and
• Clean and press

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