Delts 101: Overview & Functions

Delts. You often hear this word from a fellow fitness buff or from your trainer. They would often encourage you to work on these muscles. They spend lots of hours on the gym doing exercises that target this muscle area.

You may hear it a lot of time but not all of us really know what delts are.  Which specific muscles are they and what are their functions? Continue reading to get answers to these questions.

Delts 101: Overview

We often associate delts with our shoulders. While this could be partially true, deltoid muscles are not synonymous to shoulders.

The deltoid muscle is a round, triangular muscle that is located on top of your shoulder and uppermost part of your arm. Because of its triangular shape, the name was derived from the Greek letter delta.

Tendons attach the deltoid to the skeleton at the humerus (upper arm bone), scapula (shoulder blade) and clavicle (collarbone). Deltoids are at their widest at the top of your shoulders. They travel down your arm and narrow to its apex.

Though deltoids are most commonly known for its slang as “delts”, they were previously called the deltoideus. Anatomists are still using this name to this date.

Anatomically, distinct sets of fibers make up your deltoid muscles. Electromyography suggests otherwise though –  it’s made up of at least seven groups that can be coordinated independently by the nervous system.

Humans have an average mass of of 191.9 grams, which range from 84 grams (3.0 oz) to 366 grams (12.9 oz). This round muscle is responsible for movement and stabilization of our shoulder joint.

Delts 101: Origins

The deltoid muscles can be broken down into three separate parts: clavicular (anterior) part, acromial (middle) part and scapular (posterior) part.

Let’s take a look at these parts individually.

Clavicular (anterior) Part

Your deltoid muscle’s front head,  anterior deltoid is located in the outermost layer of muscle. It lies superficial to the proximal end of the coracobrachialis, pectoralis minor, and biceps brachii short head.

The anterior deltoid is classified as part of the scapulohumeral (intrinsic shoulder) muscle group and is situated lateral to the clavicular head of the pectoralis major and medial to the lateral deltoid. The anterior deltoid has parallel orientation fibers and inferiorly runs from origin to insertion.

This part of your deltoid muscle that is located at the front of your shoulder and attaches to your collarbone allows you to rotate your shoulder inward and flex your arm at the shoulder joint.

Other names for the clavicular part are the anterior head of the deltoid, anterior delt, front delt, front deltoid and front of the shoulder.

Acromial (middle) Part

Acromial part arises around the acromion process of the scapula. This is popularly known as the lateral deltoid and is also called side delts, outer delts or middle delts. This bony extension of your scapula is essential for shoulder socket stability.

Scapular (posterior) Part

Scapular or posterior part originates from the lower lip of spine of the spacula’s posterior border. They are also known as rear deltoid or posterior delts. This part of your deltoids is responsible for lateral rotation, horizontal extension, and abduction of the humerus at the shoulder.

All of these deltoid muscles function differently. Well, it’s not a surprise since they are facing different body parts. Your anterior muscles face the front, middle deltoid muscles face the side, while the posterior delts face the back. Your deltoids are one of the movers whenever your humerus is moving at the shoulder joint.

Delts 101: Functions

Now that we understand the anatomy of deltoid muscles, let’s jump on to understanding what they do.

Understanding how our body parts function is important for us to value them and give them the proper care that they need. Just like with other body parts, our deltoid muscles play specific functions.

Stabilizes the Joint

One important function of our deltoid muscle is a joint stabilizer.

Abduction is a process when your arm is fully resting at the side of your body while you are standing erect. This position results in a line of force that pulls along the long axis of your bone. No movement is produced as your muscle contracts.

Thanks to your deltoids though, they resist the forces that pull down on your humerus by maintaining the stability of your joint. For example, if you’re carrying a heavy object such as shopping bags or luggage, your deltoids would stop the inferior displacement of your humerus from the glenoid cavity.

Flexion and Medial Rotation

The anterior fibers of your deltoid muscles are primarily responsible for the flexion of your shoulder. It aids the pectoralis major to perform this movement. Because of the anterior deltoid, you can lift your arm up and to the front of your body.

It also works with pecs, subscapularis, and lats to perform medial rotation. Sometimes referred to as internal rotation, this rotational movement goes towards the midline.  

Basic Shoulder Abduction

Shoulder abduction happens when you move your arm away from the midline of your body, usually involving the rotation of the shoulder joint.

Your deltoid muscles, specifically your middle deltoid, are responsible for the abduction at the glenohumeral joint. Together with the supraspinatus muscles of the shoulder, your middle delts lift your arm away from the side of your body. The point of articulation for shoulder abduction is the glenohumeral joint which connects the scapula to the humerus.

Extension and Lateral Rotation at the Glenohumeral Joint

An extension is a type of movement that results in an increase in the angle between two body parts. The posterior deltoid helps during the extension at the glenohumeral joint.

Lateral rotation is a rotation movement away from the midline. Other transverse extensors such as teres minor and infraspinatus work together with the posterior fibers to perform lateral rotation.

Performing exercises that target your deltoid muscles is not only important in achieving strong delts.  You should also take good care of your delts if you want to avoid muscle injury and achieve optimum health.

REFERENCES:

Barclay, T. (2018). Deltoid Muscle. Retrieved from https://www.innerbody.com/image_musfov/musc12-new.html

Keil, D. (2014). The Deltoid Muscle. Retrieved from https://www.yoganatomy.com/the-deltoid-muscle-of-month-yoga-anatomy/

Deltoid Muscle – Anterior and Middle Heads. (n.d.). Retrieved from https://www.getbodysmart.com/arm-muscles/deltoid-muscle-anterior-middle-heads

Deltoid Muscle. (n.d.). Retrieved from https://www.kenhub.com/en/library/anatomy/the-deltoid-muscle

Deltoid. (n.d.). Retrieved from https://www.ivyroses.com/Define/Deltoid

BONUS:

You can also check out one of our articles about the best muscle-building exercises for shoulders.