Deltoid muscle

The deltoid muscle is one the human body’s more than six hundred muscles. The deltoid has a triangular shape, and it gets its name from the Greek letter delta, which is also triangular. The deltoid muscle is located on the upper arm and shoulder. People have deltoid muscles on both sides of the body. The deltoid muscles help people move their shoulders and arms. The deltoid consists of three parts, each of which helps control the arm and shoulder in different ways. Injury or illness that affects the deltoid muscle can it make it more difficult for people to move their shoulders or arms.

Background

Muscles play an important role in the body, with each of the three types of muscle—cardiac, smooth, and skeletal—having different functions. Cardiac muscles make up the wall of the heart and help move the heart to pump blood in the body. Smooth muscles line various parts of the body—including blood vessels, the uterus, and the intestines—and help the body complete certain tasks. Skeletal muscles are the most common type in the body. They attach to the bones and, in some places, the skin. These muscles expand and contract to help the body move. The deltoid is a skeletal muscle. The deltoids help people move their arms and shoulders.

Overview

The deltoid muscle is located on the upper arm and shoulder. The deltoid has three parts—the anterior, middle, and posterior sections. These work together to control the arm and shoulder. The anterior section of the deltoid is often what people consider the front of the muscle. It is located next to the chest. The anterior section originates at the clavicle, or collarbone. It runs down the front part of the shoulder and connects to the humerus, which is the bone in the upper arm. The anterior deltoid is the major muscle that helps people lift their arms out in front of the body, an action called shoulder flexion. This section also assists in transverse flexion, which involves crossing the arm over the chest, and shoulder abduction, which involves lifting the arm up and out to the side of the body. This part of the muscle also helps rotate the humerus.

The middle section, or acromial part, of the deltoid lies between the anterior and posterior portions. The middle section originates at the acromion of the scapula, which is a bone that connects to the shoulder joint. The middle section of the deltoid lifts the arms out to side, which is called shoulder abduction. Other muscles that make up the rotator cuff assist the middle deltoids in this movement.

The posterior portion of the deltoid originates at the spine of the scapula. The posterior section is located mostly on a person’s back. This part of the muscle stretches from the scapula across to the top of the back, over the back of the shoulder, and down the top part of the arm where it connects to the humerus. The posterior deltoids help extend the shoulder back behind the body. This section can also help rotate the humerus.

The three parts of the deltoid all connect the humerus at an area called the deltoid tuberosity. The various parts of the deltoid also all receive blood from the same main artery, the thoracoacromial artery. The cephalic vein runs between the anterior section of the deltoid and the pectoralis major, which is a powerful muscle on the human chest. This vein helps take blood away from all the parts of the deltoid.

The different parts of the deltoid muscle can either work together or against each other to create a movement. The deltoid is one of the most important and powerful muscles that helps move the shoulder joint. Though the deltoid is traditionally separated into these three sections, some researchers believe the muscle should be classified into seven different sections. These researchers have identified seven intramuscular tendons, and believe each tendon is connected to a separate group of muscle fibers.

Deltoids, like all muscles, are susceptible to injury and illness. Since the deltoid is connected the arm and shoulder, any complications with the deltoid could affect arm and shoulder movement. One common ailment of the deltoid muscle, and most skeletal muscles, is a strain. Some strains are minor and can cause soreness and slight swelling. The most serious strains could cause severely limited range of motion and muscle bulging. Another common ailment that affects the deltoids is a rupture. A muscle rupture happens when the muscle tears. Total deltoid ruptures are rare, but even partial tears can cause pain and weakness. Deltoid ruptures are more likely for individuals who receive steroid injections and people who have had trauma to the deltoid.

Another disorder of the deltoid muscles is called deltoid fibroids. Fibroids are intramuscular fibrous bands that develop in the muscle. Fibroids can make it difficult to the move the muscle correctly. Therefore, some people with deltoid fibroids cannot move their deltoids in the full range. The fibroids can also pull the scapula, or shoulder blade, back. Deltoid fibroids are not a common disorder, but they are more common in children than in adults.

The deltoid muscles help people complete important tasks and make basic movements, such as lifting the arms out to the side. Because the deltoids are important to such basic movements, people use different exercises to strengthen the deltoids and protect them from injury. Push-ups and pull-ups are two full-body exercises that strengthen the deltoids. People can also use weight lifting exercises to strengthen the deltoids. A bench press, which is an exercise during which a person lifts a bar weight from a reclined position, helps strengthen the deltoids. Other weight-lifting exercises that strengthen the deltoids include the overhead press and front raises.

Bibliography

Cothern, Brian G. “Deltoid Fibrosis.” Medscape, 8 May, 2018, emedicine.medscape.com/article/1262205-overview. Accessed 16 Apr. 2019.

“Deltoid.” Department of Radiology, University of Washington, 2019, rad.washington.edu/muscle-atlas/deltoid/. Accessed 16 Apr. 2019.

“Deltoid.” Loyola University Medical Education Network, www.meddean.luc.edu/lumen/meded/grossanatomy/dissector/mml/delt.htm. Accessed 16 Apr. 2019.

“Deltoid—Musculus Deltoideus.” IMAIOS, www.imaios.com/en/e-Anatomy/Anatomical-Parts/Deltoid. Accessed 16 Apr. 2019.

Johnson, Jolie. “The Movements that Involve the Anterior Deltoids.” Livestrong, 2019, www.livestrong.com/article/508081-the-movements-that-involve-the-anterior-deltoids/. Accessed 16 Apr. 2019.

Smith, Lori. “Deltoid Pain: Types and Treatment.” Medical News Today, 4 Jun. 2018, www.medicalnewstoday.com/articles/322031.php. Accessed 16 Apr. 2019.

Stoppani, Jim. “Shoulders.” Jim Stoppani’s Encyclopedia of Muscle & Strength. Human Kinetics, 2015, pp. 332-360.

“Thoracoacromial Artery.” HealthLine, 17 Mar. 2015, www.healthline.com/human-body-maps/thoracoacromial-artery#1. Accessed 16 Apr. 2019.

“What Is the Strongest Muscle in the Human Body?” Library of Congress, 31 Jul. 2017, www.loc.gov/rr/scitech/mysteries/muscles.html. Accessed 16 Apr. 2019.

Yoshimasa Sakoma, et al. “Anatomical and Functional Segments of the Deltoid Muscle.” Journal of Anatomy, vol. 218, no. 2, 2010, pp. 185–190.