The middle deltoid, positioned centrally on the shoulder, forms a substantial part of the deltoid muscle group, creating the rounded contour of the shoulder.

Origin:
Emerging from the acromion process of the scapula, the middle deltoid's fibers extend laterally to attach to the deltoid tuberosity on the humerus.

Insertion:
The muscle inserts onto the deltoid tuberosity, a prominence on the lateral surface of the humerus.

Function:
The primary function of the middle deltoid is shoulder abduction, lifting the arm laterally away from the body. It contributes significantly to overall shoulder strength and stability, playing a crucial role in various arm movements, including those involving lifting, pushing, or reaching outward.

Lateral Dumbell Arms Raise

Lateral Prone Raise (Reverse Fly)

Upright Row

Overhead Press

Machine Overhead Press