The Deltoid Muscle

Click to View Larger Image

The deltoid muscle is a rounded, triangular muscle located on the uppermost part of the arm and the top of the shoulder. It is named after the Greek letter delta, which is shaped like an equilateral triangle. The deltoid is attached by tendons to the skeleton at the clavicle (collarbone), scapula (shoulder blade), and humerus (upper arm bone). The deltoid is widest at the top of the shoulder and narrows to its apex as it travels down the arm. Contraction of the deltoid muscle results in a wide range of movement of the arm at the shoulder due to its location and the wide separation of its muscle fibers.

The deltoid has three origins: the lateral end of the clavicle, the acromion of the scapula at the top of the shoulder, and the spine of the scapula. Each origin gives rise to its own band of muscle fibers with the anterior band forming at the clavicle, the lateral fibers forming at the acromion, and the posterior fibers forming at the spine of the scapula. The bands merge together as they approach the insertion point on the deltoid tuberosity of the humerus.

The deltoid has three distinct functions that correspond to the three bands of muscle fibers. Contraction of the anterior fibers flexes and medially rotates the arm by pulling the humerus towards the clavicle. Flexion and medial rotation of the arm moves the arm anteriorly, as in reaching forward or throwing a ball underhand. The lateral fibers abduct the arm by pulling the humerus toward the acromion. Abduction of the arm results in the arm moving away from the body, as in reaching out to the side. Contraction of the posterior fibers extends and laterally rotates the arm by pulling the humerus toward the spine of the scapula. Extension and lateral rotation moves the arm posteriorly, as in reaching backwards or winding up to throw a ball underhand.

READ THIS NEXT

BlueChew Review: Everything you need to know before you buy

Is BlueChew safe? Is it worth the money? Our medical experts review it based on testing, research, and interviews.

Best Nootropics

Our experts compare the top nootropics in 2024 to find out which ones offer the most brain boosting potential.

Best Laser Cap for Hair Loss

Based on price, efficacy, comfort, and more, we help you find the best laser cap for your hair loss in 2024.

The Best Herpes Dating Sites

In our expert guide, find out which sites are the best for dating while living with herpes.

STDcheck.com Reviews: Is this STD testing company legit?

Our experts review everything you need to know about STDcheck, including privacy, costs, accuracy, and more.