The Deltoid Muscle what most people think about when they talk about the shoulder muscles. There are many shoulder muscles, but this page contains just a brief overview of the anatomy of the deltoid.
The Deltoid gets its name from its shape. "Delta" means "triangle", and the deltoid is the triangular-shaped muscle that covers the shoulder.
Although the deltoid is one muscle, it is sometimes divided into 3 parts. The anterior deltoid is the front portion and is sometimes referred to as the front deltoid. The middle deltoid is the side portion of the deltoid, and the posterior deltoid is the back portion.
Sometimes the deltoid as a whole is referred to as "the delts", and you may hear people say the anterior (front) delt, middle delt, or posterior (rear) delt.
Origination/ Starting Position:
Each part of the deltoid muscle starts on a slightly different place on the collar bone (clavicle) or shoulder blade (scapula), but they all finish at the same spot on the humerus.
The anterior deltoid starts on the lateral third of the clavicle.The middle deltoid starts on the acromion process of the scapula.The posterior deltoid starts on the spine of the scapula.
Insertion/ Finishing Point:
All three parts of the deltoids insert on the deltoid tuberosity of the humerus, which is a large bump on the outside part of the upper arm bone.
All three parts of the deltoids will help to abduct the shoulder, which means raising the arms out to the side.
In addition, anterior delt will also pull the shoulder forwards (flexion), turn the shoulder inwards (internal rotation), and pull the shoulder across the chest (horizontal adduction).
The posterior deltoid will do the 3 opposite motions of the anterior deltoid. The posterior delt will pull the shoulder backwards (extension), turn the shoulder outwards (external rotation), and pull the shoulder horizontally away from the chest (horizontal abduction).
All parts of the deltoids are innervated by the axillary nerve.
Note: All of the shoulder muscles are innervated by nerves that originate in the neck, and so neck problems and shoulder problems often go together.
Some portion of the deltoids will work any time your shoulder moves.
If you want to work the entire shoulder, choose exercises that focus on bringing the shoulders out to the side, like during lateral raises, and/ or focus on overhead movements, like the military press.
You can also perform isolation exercises like front raises for the anterior delt or reverse shoulder flyes for the rear delt.
Remember that the deltoids work any time you move your shoulders, a portion of the delts will work during every chest and back exercise also. Pull ups, push ups, seated rows, and chest flyes all work a portion of the delts.
Choose a variety of shoulder exercises, and mix up your workout to keep it fun and challenging.
Yours in health,
Dr. Charles PT/PT
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